Healthy, well-maintained hooves can remain strong and functional for decades—supporting horses from their first wobbly steps to their final years.

Hellhole Mare was, actually, an angel of a horse. A cherished favorite among equine hoof scientists who study Brumbies—Australia’s free-roaming feral horses—the tough but gentle bay had given birth to at least 15 foals before becoming so thin and weak that researchers opted to humanely euthanize her.

When the scientists, with heavy hearts, examined this beloved matriarch, they discovered “skin and bones” and toothless jaws, says Chris Pollitt, BVSc, PhD, head of the Australian Equine Laminitis Research Unit at the University of Queensland.

One part of her body, however, showed no signs of age whatsoever—the very foundation she’d been standing on for nearly three decades. Her feet. “Nicely beveled along the edges, strong heels, no laminitis, perfect,” says Pollitt. “You’d think they’d been trimmed by a professional.”

For Pollitt and his colleagues Hellhole Mare epitomizes the equine hoof. “She was nearly 30 years old, but she had the feet of a 5-year-old,” he says, having lived in what Pollitt considers an ideal environment for natural hoof care in an unridden and freeroaming horse. “This tells us that if a horse’s foot is properly cared for, it will be perfect when the horse reaches the end of its life.”

Horse Hooves In Utero

Hooves form remarkably fast, becoming easily recognizable within 65 days of gestation, says Simon Curtis, PhD, FWCF, Hon-AssocRCVS, a farrier in Newmarket, U.K. That’s before limbs have bones, he says.

To prevent uterine damage from fetal kicks, an unborn foal develops a gelatinous horn covering. This protective layer, called the eponychium or deciduous hoof, is derived in part from the sole and white line.

The basic hoof structure fully forms before birth, Pollitt says. But because unborn foals’ hooves never bear weight, their suspensory apparatus—where the coffin bone hangs from the front hoof wall via lamellar structures—remains underdeveloped. The lamellae, which help distribute weight and support hoof function, also do not fully develop before birth. In fact, he explains that because of that lack of weight-bearing, the embryonic hoof’s first and second lamellae form a distinct crisscross pattern, positioned almost perpendicular to each other.

The First Five Months

Healthy foals usually make a wobbly stand on their hooves within the first hour of birth, and they shed their eponychium within a few hours. Pollitt says such weightbearing triggers immediate loading of the suspensory apparatus. Within a couple of days, lamellar structure angles already reflect their new loading—taking on the oblique form they maintain for the rest of the foal’s life.

Meanwhile, their tiny hooves start growing their first palmar processes—a sort of “hook at the back of the bone to which the cartilage is attached”—which are completely absent at birth, Pollitt says.

Despite these changes, though, foal hooves evolve in neither shape nor structure after birth. “The original foal hoof is a certain size—say, the size of a cup—and it can’t grow any bigger,” he explains.

Instead, new horn grows rapidly from the coronary band, at a rate of about 15 millimeters per month, to create a new, mature hoof that widens and flattens over approximately five months, says Curtis. In general, that leaves a clearly visible horizontal “birthmark” line on the descending horn.

This creates a sort of “inverse cone” by three or four months of age, with greater width at the coronary band than the bottom, he explains. That’s, in part, because the foal’s hoof wall thickens more than threefold as it grows from the top down.

Meanwhile, other structures inside the foot—bones and lamellar attachments, for example—must grow along with the horse, Pollitt adds. “Lots of things are happening inside the hoof capsule after birth,” he says. “And all of these changes have to occur in synchrony, in a coordinated fashion.”

In general, this runs remarkably smoothly, he says. “It’s marvelous to consider what—and how many—things could go wrong,” he explains. “It’s like a miracle.”

Still, things can go wrong, especially when conditions aren’t favorable to good hoof growth. Selective breeding for big bodies and small hooves, for example, can negatively impact hoof development. Rigid or oversoft terrains can as well, as the researchers have seen in feral horses.

The first few months also represent the sweet spot for club foot development. Typically, hoof horn at the heel grows faster than at the toe, which occurs especially when foals favor walking on their toes, Curtis adds. Club feet, characterized by an upright shape, long, contracted heels, and a pronounced or bulging coronary band, can sometimes go unnoticed for months or years. In his research, however, he has found they usually appear between 20 and 110 days.

In domestic settings these early months represent a critical time for skilled, frequent trimming to prevent club feet, angular deformities, and other distortions, Pollitt says.

The Rest of the First Year

As foals continue to grow, their hooves undergo significant changes as they gradually develop into the familiar adult form.

“Suddenly we see this hoof taking on the shape that we associate with hooves—which is now a truncated, oblique cone, that leans slightly backward,” Curtis explains.

The new, mature hoof structure usually lasts the rest of horses’ lives, Pollitt says.

Minor tweaks do continue. Horn growth, for example, gradually slows to around 9 millimeters per month by the horse’s first birthday, Curtis says.

Loading patterns—which start as weanlings but become more prominent as the horse’s weight increases—also come into further play, he says. Through pressure readings he found horses “don’t stand like table legs” but, rather, favor inner (toward their midline) versus outer hoof-wall loading.

Suspecting that loading was impacting natural hoof growth patterns, Curtis sought to “separate the changes horses are preprogrammed to experience versus those in response to uneven loading.” He realized the horn compresses under the horse’s weight. That means even if the hoof grows at the same rate across the coronary band, it ends up seeming shorter or longer in different parts of the hoof due to getting smashed.

As a result, the outer angles from the sole to the coronary band appear more oblique, or slanted, and give the impression that outer walls grow faster.

“Farriers recognize this, and they say it grows more hoof on the outside,” he says. “But it’s not because of the production of horn cells; it’s because of the compression.”

Dorsal (front wall) angles also change in the first year at a rate of about one degree per month until about 10 months of age, Curtis says. “So, there’s an extraordinary change in angle.”

Hooves During the Rest of Life

Once a hoof has become mature—at around 10 months of age—it changes very little in healthy horses, says Pollitt.

“My feeling is that horse’s hooves, once grown and once properly cared for and in the right environment, will virtually outlive the horse,” he says.

“A lot of people think that they age—and they’ll tell you that they do, and they’ll supply anecdotal evidence to support that,” he adds. “But my experience is that they’re a wonderful piece of evolution that serves the horse well throughout its life.”

Even so, minor natural changes occur, Curtis says. For example, hoof wall thickness increases to about 9.5 millimeters in an adult Thoroughbred, or around 11 millimeters in other breeds. And horn growth slows to about 6 millimeters per month for adults and even to 3 millimeters per month for seniors.

Researchers on an ongoing pilot study, meanwhile, seem to have confirmed what many farriers have long suspected—that with age, hoof angles continue to mildly flatten compared to the ground, Curtis says.

Still, it’s also possible older horses simply have changing hoof angles due to evolving trimming techniques, especially as owners change farriers, Pollitt says.

Despite these minor changes, though, our sources say owners often perceive age-related changes in their horses’ hooves. “It’s such a rarity that farriers find horses with symmetrical hooves,” Curtis says, and that might be in large part due to unnatural loading rather than age itself.

Age-Related Conditions

While hooves can remain strong over time, they are still vulnerable to age-related diseases and other conditions.

Many older horses suffer from low-grade laminitis, Curtis says. It is often due to excess nutrients, which weaken the laminae by altering the endocrine system, usually in combination with obesity. Besides contributing to rotation or sinking of the coffin bone within the hoof, that excess weight causes compression, especially along the sole.

Horses with age-related insulin resistance—especially related to pituitary pars intermedia dysfunction (PPID, equine Cushing’s disease) and/or obesity—can have chronic laminitic changes, Pollitt says.

That could mean they have a healthy back half of the foot but compression and changes in blood supply to the front half, Curtis says. These issues combined with a slight change in hoof angle could make the problem even more pronounced.

“As a horse ages, you might notice some changes in its hoof that are more related to age-related health conditions, such as Cushing’s (PPID), rather than changes in the hoof due to older age,” says Shannon Pratt-Phillips, PhD, a professor of equine nutrition in North Carolina State University’s Department of Animal Science, in Raleigh. “Good nutrition will still be important to support hoof health even with confounding factors such as Cushing’s or insulin dysregulation.”

Beyond endocrine disorders, geriatric horses simply have more years of impact on their feet—meaning greater chances of injury, such as to the coronary band, Curtis says. “Older horses definitely tend to have more problems, but I think it’s more a cumulative effect,” he explains. “There’s not a single problem that’s more a 20-year-old hoof compared to a 5-year-old hoof.”

Other issues might stem from a lifetime of environmental challenges—such as feral New Zealand horses navigating through rough terrain—rather than the aging itself, Pollitt says.

Likewise, aging, retired domestic horses could suffer from poor hoof health simply because they might receive less hoof care, he explains.

“A lot of people neglect their old horses,” he says. “Of course, if the environment is soft underfoot, they’ll develop long cracks, and they might be euthanized because of the condition of their feet. And (owners) say they’re an old horse with an old foot. But I don’t believe that, intrinsically, there’s aging about the hoof.”

Older horses might also experience nutritional and environmental deficits due to their decreasing social rank, says Pratt-Phillips.

“They end up standing in the mud all the time, or not getting their full ration, because the higher-ranking horses take their place,” she explains.

“Of course, the horse is old, and there will be the assumption that it’s getting old and, so, the hoof is falling away,” Pollitt says. “But in my experience many horses reach old age with hooves that are the same as when they were 3 years old.”

Take-Home Message

Hooves are phenomenal structures built to last a horse’s lifetime. Even so, they experience major changes in shape and structure through the first year out of the womb, while they adjust to bearing the weight of the foal. Once mature, healthy and properly maintained horse hooves can remain strong and functional throughout an animal’s life—provided equine veterinarians and horse owners manage all age-related diseases.

This article is from the Older Horse 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Greater awareness and ongoing research mean fewer foals are being born with this genetic skin condition

Attention stock horse owners: Have you heard of HERDA? For the past 20 years, learning about hereditary equine regional dermal asthenia (HERDA) has been a major goal of stock horse associations and HERDA researchers alike. Up to 3.8% of Quarter Horses—and specifically up to 28.3% of those in the cow horse population—are carriers for this debilitating genetic condition that causes horses’ skin to wrinkle, stretch, and slough. While HERDA horses can be maintained with specialized management, most affected animals are euthanized due to the impracticalities of that care, the inability to be ridden, and painful scarring.

With simple genetic testing, though, owners can find out if their animals are affected by or carriers of HERDA so they can make sound management and breeding decisions. As awareness increases, the industry should see fewer foals born with HERDA—and aim to eliminate clinical cases altogether.

How HERDA Happens

In 1978 scientists first described an unusual super-elastic skin condition and suspected it might have a hereditary link. They were right: In 2007 scientists discovered HERDA arises from a simple mutation on a gene called PPIB, located on Chromosome 1. If a foal inherits that same mutation from both parents, he or she will develop clinical signs of the disease, says Rebecca Bellone, PhD, Veterinary Genetics Laboratory director and a professor at the University of California, Davis.

Scientists traced the mutation back to its origin, a 1944 foundation Quarter Horse colt named Poco Bueno, who sired 405 registered foals. The stallion possessed mutated genetic codes for defective collagen processing. Collagens build connective tissues in skin as well as in cartilage, bones, tendons, ligaments, neurological membranes, and some other tissues. The most obvious effect of these defects is abnormally stretchy and wrinkly skin, with layers often detaching from each other so the skin peels away and sloughs. These gaping skin wounds—along with any other contact wounds—heal slowly and poorly, leaving disfiguring scars.

Owners might first notice frequent lacerations, cuts, or scrapes on young horses eventually diagnosed with HERDA, but the strongest clue appears when these animals are first saddled. At this point they often start to develop wounds along the back and neck. Ultraviolet rays from the sun seem to make the condition even worse, creating new lesions and exacerbating existing ones.

However, because horses have connective tissue throughout their bodies, they might also develop problems elsewhere, says Abby McElroy, DVM, MS, PhD candidate and researcher at the University of Massachusetts Chan Medical School, in Worcester. In particular, researchers know HERDA to be associated with an increased risk of corneal ulcers as well as abnormal heart valves, she says.

“If you have an affected horse, it’s obviously very serious for both the horse and the owner,” says Tammy Canida, registrar at the American Quarter Horse Association (AQHA), whose headquarters are in Amarillo, Texas. “The humane thing to do is put the horses down in most cases.”

It Just Takes Two Alleles

Early research in 2009 revealed 3-4% of Quarter Horses, Paint Horses, and other stock horses probably have the HERDA mutation. However, most of these horses show no signs of disease because they’re merely heterozygous carriers, meaning they have only one copy of the HERDA mutation.

Genetic material comes from both parents equally, as genes from the mother line up in the DNA on the chromosome with matching genes from the father, Bellone explains. Genes often exist in alternate forms, which are called alleles. If an individual gets a different allele from each parent for the same gene, he or she is heterozygous for that gene. If the alleles are the same, though, the individual is homozygous.

Because HERDA is recessive, horses must have acquired the mutated allele from both parents—meaning they’re homozygous—to show clinical signs, Bellone says. Therefore, horses that acquire the mutation from the dam or the sire alone are heterozygous and seem perfectly healthy. Meanwhile, they’re carrying the DNA for the disease. If heterozygous horses are bred to other heterozygous horses, their offspring could inherit the mutated allele from both parents, Bellone says. The resulting cross has a 25% chance of producing a homozygous individual—one with clinical HERDA.

Before 2007 breeders sometimes used trial and error to identify silent HERDA carriers in their breeding stock. But since the development of the DNA test for the HERDA allele, breeders have had a simple tool for recognizing carriers, Bellone says.

“That’s the thing about HERDA; it’s recessive,” she says. “So you can avoid producing an affected animal by knowing what the genotypes of the parents are.”

High-Performance HERDA Carriers

If there’s a DNA test for HERDA carriers, why wouldn’t we just sterilize all mutant-gene horses and eliminate the allele entirely?

The answer might be due to an ironic HERDA twist. As it turns out, there might be a link between a single HERDA allele and good athletic performance. In fact, three of today’s top cutting horse sires are HERDA carriers, says McElroy. So the demand for these genetic lines remains high. And that’s no secret to the AQHA.

“It seems to be in popular lineages that are performing well in the industry,” Canida says.

The reason for that link remains a mystery, says McElroy. “I think that’s a big question within the industry: Why are there so many super-performing carriers?” she says, adding that research is lacking.

Some people in the stock horse industry suspect the mutation might code for more joint mobility in heterozygous horses without causing the deleterious effects of the gene, she explains. “Maybe they have a little bit of the phenotype,” she says, a technical term for observable characteristics.

McElroy wonders if subtle changes in connective tissue might improve performance in athletes in general—both horse and human. “You look at swimmers and gymnasts, for example,” she says. “They’re obviously incredibly hypermobile. But they’re not ill. And for horses working in cutting and reining, that hypermobility would give them a huge athletic advantage.”

Even so, if the allele endows stock horses with a “superpower” that garners many winnings early in the horses’ careers but then leads to bone and joint conditions such as osteoarthritis later in life, it could pose a welfare issue, McElroy adds.

Thus far, scientists have neither studied these questions nor measured the degrees of equine or human joint hypermobility with regard to connective tissue quality. And there has been no research completed on bone and joint health specifically in HERDA carriers. “That’s something that really needs to be studied, in my opinion,” McElroy says. “At this point, it’s unclear if an athletic advantage truly exists. It’s also unclear if any perceived advantage comes from the HERDA mutation or another gene.”

DNA Testing: Quick, Easy, Affordable, and Important

With HERDA carriers’ successful performance careers and breeding popularity, genetic testing has never been more important, our sources say. “The number of carriers right now is astronomical,” McElroy says. “So people really need to make informed decisions before breeding.”

The AQHA and American Paint Horse Association (APHA) agree. To minimize the breeding of homozygous foals, the associations have teamed up with Bellone and other experts to create educational materials and offer easy instructions for owners to have their horses’ DNA tested. A simple HERDA DNA test requires a few strands of mane and costs $45 through the UC Davis Veterinary Genetics Laboratory, or $100 as part of the full AQHA/APHA genetic testing panel.

Since 2015 the AQHA has required that owners of all breeding stallions have their studs’ genetic HERDA information on file and accessible to mare owners. In 2018 the APHA followed suit. Foals can only be registered with the AQHA and APHA if their sires’ genetic information, including HERDA status, is on file with the association.

Being heterozygous doesn’t exclude the stallions from breeding, however. Canida explains that the goals of the test are purely informational. “We always recommend that mare owners ask stallion owners for the information that would impact their breeding choices,” she says. “But we also make it public information, so that they can always pull the record and see it on our files as well.”

The associations do not require owners to test broodmares, but they strongly encourage it—especially when considering breeding to a heterozygous stallion. “If mare owners are aware that the stallion they want to breed to is a carrier, then they need to test the mare to ensure that they don’t produce any affected animals,” Bellone says.

 “We feel that our goal is to educate the members about it so they can make the choices for their breeding barn,” says Canida. “We just want them to be aware of what a horse may or may not have.”

“And under current rules, it will not be eliminated,” she adds. The AQHA’s focus, she says, is on education so as “to avoid getting those (clinically) affected horses.”

Meanwhile, nonbreeding stock can also undergo DNA testing if their owners suspect they’re homozygous or even heterozygous for HERDA, or if they’re just curious, our sources say. Both the AQHA and APHA websites provide educational tools that help owners understand DNA test results and how to manage their horses accordingly.

Importantly, awareness—even of the tests themselves—remains key, stresses Bellone. “If the genetic test exists, but people aren’t using it, it’s not helping,” she says.

Managing (and Surviving) HERDA

While the main goal is preventing the birth of any homozygous foals, the harsh reality is such births persist, our sources say. Our sources say most affected adult horses end up being euthanized, some are shipped for slaughter, and a few are rescued by nonprofit organizations. Some homozygous mares serve as embryo transfer recipient mares. Occasionally, owners keep their own homozygous foals as well-protected pets. McElroy says she recalls the case of a homozygous horse that successfully worked cattle for eight years—although it’s possible the horse had, for reasons unknown, a milder form of the disease.

If their quality of life permits it, HERDA horses could be kept in indoor conditions during daytime hours to prevent sun rays from breaking down collagen, she says. Owners would have to ensure the environment is low-risk for contact injuries—even rubbing against surfaces—and for insect bites. “There are owners who have kept these horses going for many years, keeping them inside during the day, turned out at night with intensive fly management, staying away from … anything that’s going to traumatize the skin,” McElroy says.

Management methods for similar connective tissue disorders in humans and smaller animals have progressed in recent years because these individuals’ environments can be more easily controlled. Unfortunately, that’s not the case for horses. “We just don’t know much about keeping these horses going longer,” she says.

“At this point, we don’t have a lot of therapies or treatments,” McElroy says. “It would really just be intensive management.”

HERDA on the Horizon

In the past two decades, HERDA researchers have mostly studied the condition’s effects on the skin, but they’ve started looking into its effects elsewhere in the horse’s body. For example, homozygous horses have thinner corneas with more frequent ulcers, and they have weakened heart valves.

“Collagen is everywhere, so it affects every bodily system,” says McElroy, who studies HERDA as an equine model for Ehlers-Danlos syndrome—the general HERDA analog affecting humans, rabbits, cats, dogs, cattle, sheep, and mink. “There’s a lot we don’t know about. Do they have bone fragility? What’s going on with their GI tract? Are they more likely to colic? Are they more likely to have bladder ruptures as foals?” Her own work has focused on the nervous system and confirms—like in humans with Ehlers-Danlos Syndrome—HERDA horses have abnormal spinal cord regions in the sacrum area, although the physical implications remain unclear.

Scientists are also considering whether HERDA affects some horses more severely than others—with some, like the exceptional HERDA working cow horse, having such mild disease it might even go unnoticed. “For me the question has always been, ‘Are there some underlying genetics that can protect some horses?’ ” Bellone says. “And also, ‘Is there any hope of testing for something like that, or doing any kind of research on it?’ ” To her knowledge, at this time, there is not.

An upcoming research area for such diseases is gene therapy, which essentially involves injecting the healthy allele via a viruslike vector into newborns, effectively replacing the bad allele, McElroy says. Better yet, gene therapy could start after genetic testing of the embryo. While progress is underway for humans, the astronomical price of such therapy—reaching seven figures—is likely to preclude its commercial use in horses. “It would be more like on a research basis,” she says, adding that costs might drop over time and especially with prenatal treatment.

Meanwhile, scientists and associations are continuing to focus on awareness, making sure owners understand what HERDA is and how to prevent it through DNA testing and wise breeding. Efforts so far have been fruitful, McElroy adds, with a drop in the number of homozygous foals born.

Whether the incidence of the allele itself is dropping remains hard to say, notes Bellone. With the steep increase in testing, it’s difficult to compare today’s rates with those from the mere hundreds of horses tested 15 years ago. Even so, ongoing analyses suggest there’s a trend toward a drop in allele frequency, she explains.

“We need to continue that push for education and make sure that people really understand the genetics of a recessive disease, and make sure they understand the risk of carrier-to-carrier matings,” McElroy says.

Take-Home Message

As scientists progress in their understanding of HERDA, so must the owners and breeders managing and producing the horses that carry the alleles responsible for this recessive disorder. With improved awareness and ongoing investigation into the whole-body effects of this disease, the industry is striving toward prevention and—potentially in the distant future—a hope for therapeutic management.

The Kester News Hour at the annual American Association of Equine Practitioners Convention showcases key developments around the globe in equine research. In the 2024 edition Maria Schnobrich, VMD, Dipl. ACT, of Rood & Riddle Equine Hospital in Lexington, Kentucky, highlighted three recently published equine reproduction studies.

Factors Affecting Mare Pregnancy Rates

The researchers’ objective in the first study Schnobrich described (Pasch et al., 2024) was to evaluate how the number of straws provided as a breeding dose—as well as other mare, stallion, and management factors—affected pregnancy outcomes with cryopreserved semen.

“The key takeaway message was that mares may not need to be checked as frequently for ovulation as previously thought,” said Schnobrich. “The pregnancy rates were similar for mares bred one time up to six hours post-ovulation compared to mares bred within three hours of ovulation.”

The researchers conducted this retrospective study over 11 years and included 624 estrous cycles. They induced ovulation in the mares with deslorelin (a synthetic analog of gonadotropin-releasing hormone), which is a common technique. The authors compared a single insemination post-ovulation versus a timed protocol with insemination occurring approximately 24 hours after they administered deslorelin and pre ovulation, and again within six hours post-ovulation.

“These are exciting findings because it means we don’t need to be as panicked to tighten the ovulation to insemination window post-ovulation,” said Schnobrich. “And, for the stallions in this study, there was no significant effect of the number of straws used for insemination on pregnancy rate.”

Effects of Obesity During Pregnancy in Horses

Schnobrich presented a study (Robles et al., 2023) in which the researchers described the effects of obesity during equine pregnancy on placental structure, gene expression, and colostrum and milk fatty acid concentration.

“This study built on the findings from a previous study demonstrating a negative impact of obesity in pregnant mares on their offspring (Robles, 2018),” said Schnobrich. Specifically, foals born to obese dams had higher inflammation and increased prevalence of osteochondrosis lesions (53%) at 6 months of age compared to foals born from normal body condition mares (10%).

In this equine reproduction study the researchers compared placentas and milk quality in obese mares and normal mares. They did not observe any significant differences in the placentas between the two groups, but they found the colostrum from obese mares lower in medium-chain fatty acids, and their milk had a more proinflammatory profile.

“These findings again emphasize that obesity in the pregnant mare should be avoided,” said Schnobrich. “As we see an increase in obesity in our population of broodmares, this further highlights our need to be diligent about a healthy body condition during pregnancy.”

Equine Pregnancy Success Rates After Twin Reductions

Veterinarians eliminate equine twins by manual crush of one twin approximately 14 to 16 days post ovulation with minimal adverse effect on the remaining pregnancy. For those that either go undiagnosed until later in pregnancy or have not naturally reduced on their own, the options for elimination include transvaginal aspiration. This method, however, offers approximately a  50% chance of success.

Schnobrich presented a retrospective study (Sielhorst et al., 2024), in which the researchers examined nine years of data on dizygotic twins (the result of two separate eggs) reduced using transvaginal ultrasound-guided aspiration. They studied a variety of factors (i.e., position of pregnancy, medications used, technique of procedure), and considered pregnancy outcomes at three different time points following the pregnancy (five to seven days, three to four weeks, and at live foal delivery).

“This study helps us understand when to utilize this procedure and what helps optimize outcomes,” said Schnobrich. “Intervention in most cases of twins is required as in cases of bilateral twins (one pregnancy in each uterine horn). Most that are there at 16 days post-ovulation will be there at 40 days.”

The authors recommended veterinarians reduce one twin between Days 28 and 32, and definitely before the endometrial cups form at Day 35, so the mare can be bred back if she loses the pregnancy.

Take-Home Message

Schnobrich said these equine reproduction studies offered practical implications for veterinarians and breeders and that, collectively, the findings emphasize the importance of timely interventions, careful monitoring of broodmare condition, and evidence-based decision-making.

The Kester News Hour at the annual American Association of Equine Practitioners Convention highlight key advancements in equine research worldwide. In 2024’s edition Carrie Finno, DVM, PhD, Dipl. ACVIM, professor of veterinary genetics and the Gregory L. Ferraro Endowed Director of the Center for Equine Health at the University of California, Davis, and Katie Seabaugh, DVM, Dipl. ACVS, ACVSMR, associate professor of equine sports medicine and rehabilitation at Colorado State University, in Fort Collins, shared their top picks from recent studies in their areas of practice interest.

Studying Graying Speed and Melanoma in Horses

Finno began with research by Rubin et al. (2024), in which researchers identified a genetic variation in horses that determines their greying speed and melanoma incidence.

“Graying is caused by a duplication of a 4.6 kb (kilobase, a unit of measurement used to help designate the length of DNA or RNA) intronic sequence in syntaxin 17 (STX17),” said Finno. “If horses have one copy of the variant, then they are not gray. Gray horses with two copies of STX17 gray slowly and have lower rates of melanoma but, if a horse has three copies, then they are the fast-graying horses linked with melanoma.”

For example, if a gray mare has the genes G3/G1 and the gray stallion is G3/G1, then the foal could be G3/G3, meaning he or she will gray very fast and has a higher likelihood of developing melanoma. The results could lead not only to better identification of horses likely to gray early or pass on gray-with-age genes but also to a better understanding of how the mutation affects horses’ health.

Detecting Atrial Fibrillation in Horses

In the second study Finno covered (Vernemmen et al., 2024), researchers described a method for veterinarians to detect atrial fibrillation in horses using an implantable loop recorder (ILR).

The ILRs can be placed under the skin in the left lateral thorax overlying the heart, said Finno. Practitioners use these to detect arrhythmias as a possible cause of collapse, poor performance, or monitor for atrial fibrillation (AF) recurrence in a research setting. The device can now collect information and email the clinician, improving the speed with which AF can be identified.

“Be aware that some false positives can be a result of bradycardia (when the heart beats slower than normal) rather than AF because it is a human product,” said Finno. “And we need to appreciate that AF is likely genetic.”

Identifying A Cause of Neck Pain in Horses

Seabaugh presented a study (Hendersen et al., 2024) in which researchers described the incidence of neck pain without neurologic disease in horses with transposition of the ventral lamina from C6 to C7 of the cervical vertebrae.  

“The ventral lamina is part of the transverse process, and this ventral aspect of C6 can move to the C7 vertebra,” said Seabaugh. “When located on C6, the longus colli muscle attaches to the ventral lamina, which is a cervical flexor. Movement of the transverse process likely affects the biomechanics of the neck.”

In the retrospective study, researchers looked at radiographs taken from 2020 to 2022, including a total of 135 horses. Reasons for radiographs included routine neurologic exam, neck pain, and performance-related behavior changes.

Key findings were:

1. The researchers saw transposition in 20% of the horses that was not significantly associated with a final diagnosis, meaning an equal number of horses with or without the transposition fell into each diagnosis; and
2. Transposition was more common in horses that demonstrated pain during palpation of the neck (31%) than those without pain (18%).

Additionally, 63% (17 out of 27) of the horses with transposition were Warmbloods.

Prevalence of Neck Pathology in Warmblood Horses

Looking at Warmbloods more closely, Seabaugh presented a second study (Sue Dyson et al., 2024) where researchers described the prevalence of C6 and C7 transposition in the breed.

“This study included only Warmbloods: 127 controls and 96 horses with neurologic abnormalities, neck pain or stiffness, or neck-related forelimb lameness,” Seabaugh said. The researchers found 24.2% of horses had C6 and C7 transposition. Horses without neurologic issues (the controls) were more likely to have this variation than those with neurologic abnormalities.

“The conclusion from both studies was that there is no association between C6/7 transposition and neurologic disease, and it is just a variant occurring in up to one-quarter of all horses,” said Seabaugh.

Updated ACVIM EHV Consensus Statement

Finno broke down the updated ACVIM consensus statement for equine herpesvirus (Lunn et al., 2024) for the audience.

Three key takeaways from the new guidelines included:

1. Researchers have seen minimal evidence that the vaccine protects horses against equine herpesvirus-1 infection, but they still recommend vaccinating.
2. Pharmacological treatments have minimal effect (except valacyclovir if administered in advance).
3. In large outbreaks nasal swabbing typically suffices for diagnosing affected horses; however, when abortion occurs on the premises, veterinarians need to test blood samples.

In a study following the herpesvirus outbreak in Valencia, Spain, “Sixty-eight percent of horses with neurologic disease returned to exercise, and over half returned to full performance,” said Finno. “But the less ataxic they were on presentation, the more likely they were to fully recover. If there was urinary and vascular compromise, then they were more likely to be euthanized.”

Mares can get a bad rap for recalcitrant estrous behavior, but hormones and tumors could also be at play

Anormal mare should behave just like any other horse. So says Paula Hitzler, longtime farm manager at the Michigan State University Horse Teaching and Research Center, in Lansing.

Over her 35 years at the center, home to one of the nation’s oldest Arabian horse breeding programs, Hitzler has seen herds of as many as 125 horses. When The Horse spoke with Hitzler in early 2024, the herd size was 68. Though just 15 of those horses were broodmares, most of the horses kept at the farm are mares because colts are typically sold after they’re started under saddle.

“In my opinion, (with a) normal mare, you should not know by working with her if she’s a mare or a gelding,” Hitzler says. “She should just be a solid citizen.”

Even in estrus it’s rare for otherwise pleasant, healthy mares to display sour temperament, Hitzler says.

“I don’t think that very many mares are ‘mareish,’ ” Hitzler says. Behaviors such as being grouchy, showing signs of heat around people, or urinating while being groomed—“I don’t see very much of that.”

Rather than ignoring or blowing off grouchy behavior as a normal side effect of heat cycles, Hitzler sees “bad” behavior as a potential warning sign that something has gone awry in the mare’s body; maybe the mare’s hormones are out of whack, or maybe the mare has an ovarian tumor. And, of course, mares can experience other ailments, such as injuries, gastric ulcers, or infections. Authors of a 2023 case series on behavioral disorders in mares with ovarian disorders reported that veterinarians must exclude nonreproductive causes of unwanted behavior and reduced performance, such as urinary tract disorders (vaginitis, pneumovaginitis, cystitis, and urolithiasis) and low-grade musculoskeletal pain. Because owners mentioned poor rideability, vets must also rule out rider factors¹.

What Is ‘Normal’ Behavior for Mares During Estrus?

Healthy breeding-age mares spend 15 to 17 days out-of-heat and five to seven days in heat, spring to fall (some sources say 14 to 16 days). Signs that a mare is in heat include receptivity to a stallion (standing when he’s around, for example), frequent urination, raising the tail, and “winking” the vulva.

Whether you find that behavior annoying or problematic depends partly on your perspective and priorities.

If you’re looking to breed your mare, obvious signs she’s in heat make your job easier—so long as the signs of heat reflect reality. If the mare is showing signs of estrus but is not in heat, then timing insemination or breeding could prove tricky.

While Hitzler’s perspective is that grouchy, sour estrous behavior isn’t super common among healthy mares, there’s long-standing scientific literature that says many horse owners feel otherwise. For people who show or compete their mares, when estrous signs do include being difficult to ride or handle, that can be frustrating.

“I did have one grouchy mare we put on Regu-Mate (altrenogest) while we were riding her just to suppress estrous behavior so she wasn’t so grouchy,” Hitzler says.

The drug keeps mares from coming into heat, and it can be useful during competition season.

Evaluating the Mare

If you’re concerned about mareish behavior, pay attention to the frequency, note it on your calendar, and call your veterinarian.

After assessing behavior, practitioners typically examine the mare’s reproductive tract, via palpation and ultrasound, for any irregularities, checking the ovaries’ appearance, relevant structures during the breeding season, and hormone levels to determine her heat cycle stage.

Trouble Ovulating?

When a mare seems to be in heat for longer than expected, it could be she is having trouble ovulating.

It turned out that one of Hitzler’s few “grouchy” mares that pinned her ears during cinching and was irritated by rider leg pressure was in persistent estrus—basically, the ovarian follicle was still developing and had not released the oocyte.

“Upon evaluation using rectal palpation and ultrasound, a persistent follicle was observed,” Hitzler recalls. “Thankfully, a dose of hCG resolved the issue. Sometimes the persistent follicle will not respond to medications. We were thankful that the mare did not have an ovarian tumor.”           

Ovaries and Tumors

Indeed, ovarian tumors can cause behavioral issues, and vets can confirm these growths with ultrasound or hormone testing.

Removing an ovary when there’s a tumor is an obvious choice. Some owners remove ovaries based on behavioral problems even when a tumor has not yet been confirmed.

In the July 2023 study mentioned above, researchers at the Veterinary Teaching Hospital of the University of Teramo, in Italy, reviewed clinical records of mares with a history of problematic behavior that had one or both ovaries removed. Researchers followed up with the mare owners and found they reported improvement in the horses’ behavior. Researchers noted histological exams later revealed granulosa cell tumors (GCTs) or granulosa teca cell tumors (GTCTs) on most of the removed ovaries.

Complaints from the mares’ owners had involved behavior problems during riding.

“They really don’t appreciate when you just try to ride them,” says Giulia Guerri, DVM, PhD, a specialist in equine medicine and surgery, resident ECVDI (European College of Veterinary Diagnostic Imaging), and a researcher in the Equine Medicine and Surgery Section at the University of Teramo.

Guerri was one of the authors of the study who cited “increased sensitivity at both flanks, general problems when ridden, and unwillingness to engage the hindquarters when ridden” as just a few of the problems common to the mares that had ovaries surgically removed.

When the veterinarians found tumors, “common behaviors were also biting or kicking other horses, kicking humans, bucking at work, pulling away from contact when asked to engage the hindquarters, and unwillingness to engage.”

Keep in mind that affected ovaries can become quite large. Normal ovaries are only a couple of inches in length, but a tumor can make them the size of a soccer ball or bigger.

“You can imagine that it’s also a problem during the riding,” Guerri explains. At that size, the ovaries pose a mechanical issue. “After the removal, you see really quick improvement (in) the behavior.”

Tumors can also disrupt hormones.

“The tumor involves specific cells of the ovary that are hormonally active,” Guerri says. “These cells can overproduce hormones (usually inhibin, testosterone, and anti-Müllerian hormone) leading to hormonal imbalances that cause ‘misbehavior.’ ”

In the case series study Guerri and her co-authors wrote, “The best option to diagnose GCT/GTCTs before surgical removal is a hormonal assay to measure the blood concentration of anti-Müllerian hormone. This is secreted by the granulosa cells in the ovary and has recently gained popularity as a potential biomarker for GCT/GTCTs.”

In an Equine Veterinary Journal study², University of California, Davis, researchers reported they were less likely to attribute bad mareish behavior to hormone problems: “Of the abnormal behaviors, stallionlike behavior was the only one that was found to have significant association with increased concentrations of the tested hormones,” the authors wrote.

UTIs and Kidney Infections

Urinary tract and bladder infections in mares can lead to frequent urination, posturing, and perineal irritation, often mistaken for estrous behaviors. Veterinarians typically examine and then treat affected mares with antibiotics to resolve these infections. 

Ridden Mares vs. Broodmares

Riding or exercising your mare can provide additional opportunities to detect that something’s bothering her. Grooming, tacking up, or riding all potentially involve touching the mare’s flanks. As Guerri points out, that pressure might be unpleasant.

Sport horse mares are common in these studies of estrus, ovaries, hormones, and how they impact mare behavior, she says. Returning a mare to productive under-saddle work is a frequent concern.

For owners of broodmares that exhibit problem behavior, there is hope; in the case series articles the authors reported that mares with just one ovary removed were able to get pregnant.

If you’re no longer riding your mare—whether she’s retired to pasture-puff status or is a broodmare—you’ll have to rely on other methods to detect unusual estrous behavior.

Entering estrus in the winter months would be one clue, Hitzler points out. You can also keep an eye out for how she behaves around geldings. Consider shifting turnout arrangements if your mare is sometimes receptive to geldings on a shared fence line. Horses could get hurt when a mare is considerably less enthused about a male horse’s attentions.

“You have to understand behavior,” Hitzler explains. “You have to understand whether this behavior is going to be dangerous for the horse.”

Reading ear, head, neck, and tail expression can help identify problems, she adds.

Other approaches, such as keeping track of food consumption, body condition score, and herd dynamics, might also provide insight.

Your Mare is Unique      

Mares are individuals. Some are spicy by nature while others are personable and sweet. Familiarize yourself with your mare’s habits and demeanor.

Hitzler recommends watching your mare’s facial expressions for clues about her mood or health.

So many people look at horses’ legs, shoulders, and feet while working with them on the ground.

“Look at their faces,” Hitzler urges. “Their faces tell you an awful lot, whether they’re content, whether they’re worried, whether they’re afraid. And then that also coordinates with the ears and neck height and body posture and tail. So, they all go together. But I think a lot of people forget that there’s a lot of facial expressions that go on with horses.”

Take-Home Message

If your mare is acting sour, there might be a health-related reason. Normal estrous behaviors include receptivity to a stallion, frequent urination, raising the tail, and winking the vulva. When estrous signs include sensitivity on the flanks, poor behavior under saddle, tail swishing, and squealing, you might consider chatting with your veterinarian.

References

1. Straticò. P.; Hattab, J.; Guerri, G.; Carluccio, A.; Bandera, L.; Celani, G.; Marruchella, G.; Varasano, V.; Petrizzi, L. Behavioral Disorders in Mares with Ovarian Disorders, Outcome after Laparoscopic Ovariectomy: A Case Series. Vet Sci. 2023 Jul 25;10(8):483. doi: 10.3390/vetsci10080483. PMID: 37624270; PMCID: PMC10458155.

2. Huggins, L. Norris, J. Conley, A. Dini, P. Abnormal mare behaviour is rarely associated with changes in hormonal markers of granulosa cell tumours: A retrospective study. Equine Vet J. 2023. doi.org/10.1111/evj.13967.

Q: What are the best feeding practices to ensure a smooth weaning transition for the foal?

A: Suckling foals grow rapidly, with most reaching 30-40% of their mature weight by weaning. Development at this rate requires a steady supply of good nutrition. Mare’s milk primarily supplies a foal’s nutrition until weaning, after which the diet transitions to some combination of feed, supplements, and hay or pasture. You can make this transition easier by introducing appropriate feeding practices prior to weaning. What and how you feed the suckling foal will impact not only his overall growth and well-being but also how well he handles weaning.

Feeding Suckling Foals

Suckling foals show interest in eating within the first weeks of life. A foal feed should be formulated with high-quality protein to supply essential amino acids and be adequately fortified with the proper balance of vitamins and minerals. The goal of supplemental feeding for suckling foals is to bridge the gap between what the mare’s milk provides and what the foal needs to grow and develop to his full genetic potential. Feeding 1 pound of a well-formulated foal feed per month of age daily will help accomplish this. For example, a 2-month-old foal should eat 2 pounds of feed per day, or roughly 1 pound of feed per 100 pounds of body weight.

Feeding mares and foals individually—not in a group—offers the most precise method to feed the foal. However, many farms don’t have the staff or the facilities to do this. Creep feeders are an option but must be monitored to make sure mares cannot get the feed and to prevent injuries around the equipment. Creep-fed foals should be grouped and fed amounts appropriate for their age. If allowed free-choice feed, foals often overeat and gain weight too fast, putting undue stress on immature bones and joints.

Mares and foals are often fed together, which can work well. As the foal gets older and needs more supplemental feed, the mare’s nutritional demands for lactation begin to decline. When feeding mares and foals together, place feeders at a height the foal can comfortably access and be sure to allow plenty of space.

Feeding Foals After Weaning

Following weaning, feed foals the same concentrate they were eating prior to weaning, but increase the feeding rate to 1.25–1.75 pounds per 100 pounds of body weight to replace the mare’s milk. If possible, divide the daily ration into smaller, more frequent meals to help with the transition from having free-choice access to the mare’s milk and nursing over 70 times a day. Weanlings have small digestive tract capacity and benefit from smaller meals.

Forage quality is also important for weanlings because they have less capacity and ability to digest hay and pasture than an adult horse. If weanlings have free-choice access to excellent pasture or hay and would become overweight eating the recommended amount of the foal feed, you might need to transition them to a ration balancer.

A ration balancer is designed to be fed to foals as well as adult horses and will provide appropriate nutrition to support lean tissue development without unnecessary calories. Routinely assess your weanling’s body condition and adjust the amount of feed offered or transition to a ration balancer if needed to support moderate body condition. This will help ensure the nutritional requirements for growth and development are met without the youngster becoming overly fat.

Take-Home Message

Suckling foals grow rapidly and need a carefully managed feed program to support healthy development and ease the transition to weaning. While the mare’s milk is the primary nutrient source early in life, introducing high-quality foal feed helps fill nutritional gaps and prepares foals for weaning. After weaning, increase feed amounts as appropriate and offer frequent meals to ease the transition from nursing, support continued growth, and improve digestive health. Monitor your weanling’s body condition and adjust his diet as needed to help him grow correctly without becoming overweight.

Do you have an equine nutrition question?

Selective treatment strategies can combat antimicrobial resistance while protecting foals from R. equi

Rhodococcus equi is a hardy bacterium that lives in the soil and horse feces. It replicates in horse manure, so on densely stocked farms such as breeding operations, the environment can become heavily contaminated. When the bacterium becomes aerosolized—primarily due to environmental factors such as wind, dry conditions, and soil disturbances—foals can inhale it, potentially becoming infected.

Two forms of the bacterium exist: an avirulent form that is essentially benign for foals and another that is a virulent form. The virulent, disease-causing form has a specific genetic element called a plasmid with a gene that codes for a protein called the virulence-associated protein or VapA.

“The VapA protein enables R. equi to replicate inside immune cells in the lungs of foals, alveolar macrophages, leading to abscesses forming in the lung. This disease process is similar to what happens in tuberculosis, where the bacterium known as Mycobacterium tuberculosis is able to replicate in alveolar macrophages of humans to cause pneumonia,” explains Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM, of Texas A&M University’s College of Veterinary Medicine & Biomedical Sciences, in College Station. Cohen is professor of equine internal medicine, Glenn Blodgett Chair in Equine Studies, and associate department head for research and graduate studies in the college’s Department of Large Animal Clinical Sciences.

Foals living on endemic farms are exposed to virulent R. equi from birth and can become infected at a very young age. But most foals don’t exhibit clinical signs of pneumonia until they are 1 to 3 months old or older. Signs in foals resemble what we would see in a child: fever, lethargy, and coughing.

Experts say R. equi pneumonia poses significant challenges for the equine
industry due to a number of different factors, including:

1. The high costs of prevention/treatment;
2. The economic losses associated with foal mortality in severe cases; and
3. The reduced athletic potential of recovered foals as adults.

Further, antimicrobial resistance to medications often used to treat this condition adds to the complexity of managing R. equi.

In this article we’ll review some important facts about diagnosing and treating R. equi pneumonia, address issues related to antimicrobial resistance, and describe the work underway to create a not-so-secret weapon to fight this historically indomitable bacterium: a vaccine.

Fact No. 1: R. equi infection often leads to a self-resolving subclinical (without obvious clinical signs) pneumonia that typically does not need to be treated.

Veterinarians first started using thoracic ultrasonography in 2001 to screen foals for the presence of abscesses within the lungs suggestive of R. equi pneumonia.

“Studies conducted in 2005 and 2008 indicate that thoracic ultrasound screening and treatment of subclinical cases decreased the incidence of pneumonia and decreased the number of hospitalized foals,” says Angela Bordin, MS, PhD, assistant professor in the Department of Large Animal Clinical Sciences at Texas A&M.

This led to the widespread adoption of a screen-and-treat approach, where veterinarians began treating foals with evidence of pulmonary abscesses, even if the foals showed no clinical signs of pneumonia. 

In additional studies researchers discovered the following:

Fact No 2: Thoracic ultrasound exams at farms with endemic R. equi show that often more than 50% of foals are subclinically infected.

Fact No. 3: An estimated 70-85% of subclinically infected foals heal over time without treatment.

“This information led to the realization that not all foals with lung abscesses attributed to R. equi need to be treated,” explains Cohen.

But it was too late.

The Screen-and-Treat Fallout

“Thoracic ultrasound allows us to identify foals that have a lesion/abscess in their lungs before they have clinical disease,” says Bordin. “These lesions can progress to a severe pneumonia. Given there is no vaccine available, and the variability associated with Re-HIP administration (that of R.-equi-specific hyperimmune plasma), it is understandable that thoracic ultrasound seemed an attractive way to detect and treat foals with subclinical pneumonia.”

Avoiding R. equi infection is important because of the economic and welfare implications for farms and their horses.

“But the screen-and-treat strategy came with a price,” she continues. “Antimicrobial resistance in clinical isolates of R. equi from foals was rare before 2001, but it increased significantly after thoracic ultrasound screening. To exemplify, one study documented a higher prevalence of multidrug-resistant R. equi from 2007 to 2017 compared to 1999 to 2006 (Huber, 2018). In another study multidrug-resistant R. equi were isolated from soil samples of 76 out of 100 horse-breeding farms (Huber, 2019).”

Cohen concurs, adding, “As a result of the widespread, unnecessary use of antibiotics in foals without clinical signs of pneumonia, strains of R. equi resistant to the class of antibiotics most effective for treatment of rhodococcal pneumonia in foals began to emerge.”

A Closer Look at Antimicrobial Resistance to R. equi

“Antimicrobial resistance in R. equi is primarily driven by the acquisition of plasmids, which carry resistance genes for multiple antibiotics, including macrolides, aminoglycosides, and tetracyclines,” says Laura Huber, DVM, MSc, PhD, Dipl. ACVPM, assistant professor at the College of Veterinary Medicine, Auburn University, in Alabama. “These plasmids enable horizontal gene transfer between bacteria, allowing R. equi to rapidly acquire and spread resistance within microbial communities.”

Huber explains that the accumulation of antimicrobial residues from past antibiotic use can persist in the environment for many years, creating ongoing selective pressure that helps sustain antimicrobial resistance even after antibiotic use ends. In other words, the lingering antibiotics allow bacteria possessing resistant genes to survive and reproduce while killing off susceptible bacteria, leading to a population dominated by resistant strains over time.

“Our team is investigating the potential impact of antibiotic treatments in foals on the contamination of horse farm soil with antimicrobial residues,” says Huber. “We’re specifically studying how long these residues persist in the soil and how they contribute to the maintenance and spread of antimicrobial resistance, focusing on the long-term environmental effects of antibiotic use in animal care.”

And antimicrobial resistance can spread between different bacteria and species, creating a significant risk to other animals and humans.

“Rhodococcus equi is an ideal model for the One Health concept, as it links human, animal, and environmental health,” explains Huber. “The bacterium can be transmitted from the soil to both animals and humans, illustrating the interconnectedness of environmental, animal, and human health in the spread of infectious diseases and antimicrobial resistance.”

Treat for R. equi When Needed

Despite the bleak picture as far as R. equi antimicrobial resistance, Cohen stresses the importance of recognizing sick foals.

Fact No. 4: Foals diagnosed with R. equi pneumonia should be treated.

“The challenging part for veterinarians is that we do not yet know which foals will self-cure and which will require treatment,” says Cohen.

He and other experts say vets can make an R. equi pneumonia diagnosis based on:

• Farm history of R. equi pneumonia;
• Foals 1 to 6 six months old on the farm;
• The presence of appropriate clinical signs;
• Thoracic ultrasound or X rays showing lung abscesses or consolidation (areas filled with a substance besides air);
• Blood work showing a high white cell count and elevated concentration of inflammation-associated proteins such as fibrinogen or serum amyloid A; and
• Culture and microscopic examination (cytology) of a sterilely collected aspirate from the upper respiratory tract (trachea/bronchioles) to isolate and visualize bacteria and, ideally, identification of the VapA gene by polymerase chain reaction test (PCR).

Fact No. 5: Vets should not rely solely on thoracic ultrasonography to decide which foals to treat.

Further, veterinarians should not rely solely on blood work, such as a complete blood cell count, to diagnose R. equi; it’s better to also have cytologic or PCR evidence.

Fact No. 6: Foals infected with resistant strains of R. equi have a significantly lower survival rate compared to those infected with antimicrobial-susceptible strains.

When treating foals, experts have long recommended using a combination of rifampin and the macrolides azithromycin, clarithromycin, or tulathromycin. When resistance to rifampin exists, veterinarians can use the tetracycline antibiotic doxycycline as a substitute. But are these substitutions as effective as the rifampin/azithromycin combination once was?

“There needs to be more research on that,” Bordin says.

Preventive Strategies: The Elusive Vaccine and Re-HIP Therapy

Fact No. 7: Preventing disease is preferrable to overtreating. The goal of a prevention program is to reduce clinical pneumonia cases, thereby decreasing antimicrobial use and the subsequent development of antimicrobial resistance.

Vaccination

For many infectious diseases, vaccination has proven to be an effective preventive measure, decreasing the incidence and severity of diseases. But R. equi has proven a difficult pathogen for vaccine creation.

Various factors contribute to the challenge of developing a vaccine for R. equi. For example, this is an intracellular pathogen, and we lack a clear understanding of the immunity that protects against it.

“Foals are exposed to R. equi from birth and are most susceptible to infection when they are very young,” Cohen explains. “Their immune systems are naive and immature such that many foals can’t mount effective immune responses. But we know that giving foals the virulent organism in large numbers by stomach tube provides protection against infection, so we know that they can mount protective immune responses within the first few weeks of life.”

In his most recent attempt at creating a vaccine, Cohen, together with his research team, created a messenger RNA (mRNA) vaccine that encodes the VapA protein. After delivery—injection, in this case—the vaccine produces VapA in small amounts, which stimulates the foal’s immune system to mount immune responses to virulent R. equi strains. These immune responses are innate, meaning a general defense that happens immediately, and adaptive, which is a more specific response that occurs later.

“The vaccine did not work very well when delivered via nebulization directly to the lungs,” he notes. “When we gave it intramuscularly, that seemed to stimulate immune responses.”

Cohen says additional studies are needed to further determine if this mRNA vaccine is indeed worth pursuing in foals, or if efforts should return to producing an mRNA (or other) vaccine administered to pregnant mares instead.

“Vaccinating the mares may result in the production of antibodies against VapA that can be transferred to their foals through the colostrum and milk to protect the foal during the highly vulnerable period in the first weeks of life,” says Cohen. 

R. equi-Specific Hyperimmune Plasma (Re-HIP)

Most farms with endemic R. equi rely on Re-HIP for preventing infection in young foals. These plasma products are produced from mares vaccinated against R. equi using a product designed for adult horses. Foals receive Re-HIP intravenously shortly after birth, but the mechanism of action is unclear.

Although the approach was once considered controversial as far as its efficacy, Cohen says, “The bulk of the evidence indicates protective effects of transfusing hyperimmune plasma to foals, but the protective effects are not complete and vary among plasma products, farms, and individual foals. While we need better evidence in the form of well-controlled trials to get clearer evidence, current knowledge indicates that Re-HIP is the best prevention that we have available at this time.”

Fact No. 8: Experts recommend administering 2 liters of Re-HIP that has high activity against VapA to foals within the first day of life.

This conclusion is based largely on studies conducted by Cohen’s team, including a pinnacle study by Susanne Khan in 2019 published in Equine Veterinary Education.

“I think at most endemic farms, it makes sense both medically and financially to transfuse with anti-rhodococcal plasma because there is no effective alternative for controlling R. equi pneumonia,” says Cohen.

However, he notes that the advantages of Re-HIP are not as apparent on nonendemic horse farms.

“The decision as to whether to use Re-HIP needs to be made by the farm veterinarian, farm manager, and owners of the foals to assess both the risk of the disease and their levels of risk aversion,” Cohen says. “At nonendemic farms it is less clear whether costs and risks of Re-HIP outweigh the potential benefits of preventing something that may not be present.”

Future Directions in R. equi Research

Veterinarians gained valuable insights into R. equi through routine treatment following thoracic ultrasound screening in the early 2000s (based on the work of Steeve Giguère, DVM, PhD, Dipl. ACVIM, and others). However, our sources say much more research is necessary to get ahead of this economically draining disease. Specifically, vets need effective and efficient preventive strategies, ideally in the form of a vaccine, to prevent neonatal morbidity and mortality. 

“Because of limited availability of research funding, it will take years for researchers to test their ideas surrounding mare and foal vaccines,” says Cohen. “But we are nothing if not persistent and will continue to work hard to try to investigate an approach to protect foals.”

On the antibiotic-resistance front, Huber adds, “Responsible antibiotic use can slow the spread of antimicrobial resistance.”

She says veterinarians should use ultrasound to detect R. equi early and institute more targeted management, rather than relying on the screen-and-treat program. This approach would help reduce unnecessary antibiotic use. “Developing clear guidelines that combine ultrasound findings with clinical signs is crucial to avoid overuse of antimicrobials and ensuring that antibiotics are only administered when truly necessary,” says Huber. “While these approaches can help manage antimicrobial resistance, fully reversing the damage will require broader strategies, including improved (antimicrobial) stewardship and environmental control.”

This article is from the Spring 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Newborn foals need colostrum—the first milk a mare produces after giving birth—to receive vital antibodies that help protect them from disease. To build strong early immunity, foals must consume colostrum within the first 24 hours of life, while they still can absorb those antibodies.

In some cases, if a mare produces poor-quality colostrum or if a foal doesn’t get enough colostrum or can’t absorb the antibodies, it can lead to failure of transfer of passive immunity (FTPI)—commonly called failure of passive transfer—leaving the foal more vulnerable to illness and less likely to survive.

In a recent study, researchers at the University of Glasgow, in Scotland, including Kirsty Gallacher, BVMS, MRCVS, MANZCVS, Dipl. ACT, and Katherine Champion, MSc, examined the relationship between mares’ colostrum quality and foals’ weight and immunoglobulin G (IgG) levels. Katie Denholm, BVMS, MVSc (Epi), PhD, senior clinician at the university’s School of Biodiversity One Health and Veterinary Medicine, said the group measured associations between:

• Foal risk factors such as sex, birth weight, month and year of birth, and serum Immunoglobulin G (IgG) concentration;
• Dam age and colostrum Brix (%)—a method using a Brix refractometer that measures the concentration of solids contained in the colostrum such as antibodies);
• Serum IgG and daily and weekly live weight gains; and
• mare colostrum Brix (%) and foal serum IgG concentration (measured between 12 and 24 hours after birth).

Examining Mare Colostrum IgG, Foal Serum IgG, and Foal Weight

The researchers weighed and measured the serum IgG concentrations in a total of 535 Thoroughbred foals within 20 hours of birth daily for the first seven days of life, and then weekly until the foals were 130 days old. They also measured colostrum in the 177 mares, finding a moderate correlation between foal serum IgG concentration and mare colostrum IgG concentration (as estimated by Brix). However, foal serum IgG concentration did not significantly correlate with foal average daily weight gain during the study.

Denholm said while sex of the foal was not significantly associated with serum IgG concentrations, for every increase in foal birth weight (per kilogram unit), the research team saw small but significant increases in foal serum IgG concentration (0.04 grams). However, when they investigated weight categories, foals in the higher birth weight categories tended to have lower serum IgG concentrations. “Veterinarians tend to be concerned for the overall health status of lower birth weight foals, but our findings may raise increased concern for large birth weight foals and for due diligence in testing serum IgG levels in all foals,” she said.

Denholm and her research colleagues also found that foals born later in the year had lower colostrum Brix (%) values and gained less weight per day on average, compared to those born earlier. Additionally, “increasing dam age at foaling was linked with lower colostrum Brix (%), and serum IgG (grams/liter) concentration was associated with year of birth of the foals, foal birth weight (kg) and colostrum Brix,” Denholm said.

For every percent increase in mare colostrum Brix, Denholm observed small but significant increases in foal serum IgG concentration (0.25g/L). “Of the 112 colostrum samples with low Brix, 89 resulted in foals with serum IgG concentrations less than 4g/L (indicating FTPI),” said Denholm. “This suggests that further high-quality colostrum supplementation for these foals (as per breeding farm protocol) may not be happening promptly enough to allow for absorption through the foals’ neonatal enterocytes (specialized cells in the small intestine of neonates that play a vital role in absorbing colostral milk proteins such as immunoglobulins) before they become impermeable to large IgG molecules.” This can potentially compromise foal immunization and long-term health.

Take-Home Message

Denholm and her fellow researchers noticed a correlation between mare colostrum quality and foal IgG levels; however foal IgG levels did not commonly correlate with their weight gain. Larger newborn foals likely need a higher volume of high-quality colostrum shortly after birth to confirm passive immunity, said Denholm. Over the course of the study, Denhom and her team noticed a trend toward larger foals, which highlights the need for colostrum management and quick decision-making regarding therapeutic dosage by breeders and veterinarians.

The study, “Mare colostrum quality and relationship with foal serum immunoglobulin G concentrations and average daily weight gains,” was published in Equine Veterinary Journal in January 2025.

Dysphagia, or difficulty swallowing, can have serious consequences for foals. At the 2025 Cavalcade Education Equine Reproduction Seminar, held on Jan. 8, in Red Hook, New York, Lauren Holley, BVSc (Hons), Dipl. ACVIM, of Rhinebeck Equine, also in New York, explained the importance of diagnosing dysphagia in foals early and properly managing them to prevent respiratory dysfunction and aspiration pneumonia.

Critical First Steps: Assessing the Newborn Foal

Holley highlighted the importance of a neonatal physical exam at birth to catch dysphagia and other potential abnormalities early. With this hands-on physical exam, the veterinarian should evaluate:

• Vital signs;
• Heart sounds;
• Limb deformities;
• The umbilicus; and
• The respiratory system.

Signs of Respiratory Dysfunction in Foals

Aside from milk coming out of the nostrils—considered a definite sign of disease—other clinical signs of dysphagia in the foal include:

• Nasal discharge;
• Abnormal respiratory rate and effort; and
• Respiratory noises, such as stridor (abnormal sounds heard when inhaling).

“The most concerning clinical sign remains milk coming out of the nostrils, which requires immediate veterinary attention,” Holley said. “If this is observed, the foal should be muzzled and separated from the mare while waiting for the vet, as continued nursing increases the risk of aspiration pneumonia from milk pooling in the lungs.”

Causes of Dysphagia in Foals

Dysphagia usually stems from two primary issues: one functional, the other structural.Functional dysphagia occurs relatively frequently and often appears in cases involving prematurity, neonatal encephalopathy (also called “dummy foal” syndrome), or systemic illness. Structural issues, though less frequent, include cleft palates, cysts, and esophageal dysfunction.

Diagnosing Dysphagia in Foals

If practitioners suspect dysphagia in foals, they might perform blood tests to assess systemic inflammation and organ function and pursue diagnostic imaging in the form of ultrasonography, radiography, or endoscopy. “Endoscopy is considered the most important diagnostic tool as it allows us to directly visualize the upper airway and trachea for evidence of aspiration or structural abnormalities,” said Holley. Endoscopic videos can reveal weak or collapsed pharyngeal muscles, inflammation, and the presence of milk in the trachea.

Treating Dysphagia

Holley said the goals when treating dysphagia in newborn foals include three main objectives: Stop aspiration, reduce inflammation, and address secondary bacterial pneumonia. Veterinarians might treat foals that have dysphagia by placing a nasogastric feeding tube and administering anti-inflammatory medications and broad-spectrum antibiotics. In select cases veterinarians recommend antioxidants—notably vitamin E and selenium—to address nutritional deficiencies that negatively affect foals’ neuromuscular function.

Foals with severe structural abnormalities or neurologic issues might need longer-term management, such as bucket feeding rather than nursing until weaning. Veterinarians often perform repeat endoscopic evaluations on these foals to monitor their progress and guide treatment.

Take-Home Message

Dysphagia in newborn foals can be serious, but it often improves with early diagnosis and treatment. Most foals recover well, especially when the cause is functional—those cases usually resolve within five days. Because complications such as aspiration pneumonia can develop quickly, horse owners and veterinarians must act promptly, identifying the cause of dysphagia and implementing appropriate supportive care to give these foals the best chance at a full recovery.

Postpartum mares face a higher risk of developing large colon volvulus—a life-threatening type of colic in which the colon twists 360 degrees or more, cutting off blood flow and blocking the passage of gas and feed. Jesse Tyma, DVM, Dip. ACVS, a surgeon at Rhinebeck Equine, in New York, described the diagnostic and treatment approaches to this condition at the 2025 Cavalcade Education Equine Reproduction Seminar, held in Red Hook, New York, on Jan. 8.

Anatomy and Susceptibility in Postpartum Mares

Tyma described the large colon as a partially mobile gastrointestinal organ prone to displacement and twisting within the horse’s abdomen. The reason postpartum mares are especially susceptible to this condition relates to the empty space left in the abdomen after foaling, which allows the colon to shift more easily.

Diagnosing Large Colon Volvulus in Mares

The clinical signs of colic in a mare with large colon volvulus are usually severe, including vigorous pawing, violent rolling, a bloated appearance, and intractable discomfort. Tyma emphasized that prompt diagnosis and treatment are critical to the mare’s survival and foal’s safety.

“The colic exam aims to assess the postpartum mare’s overall health status, localize the lesion, and differentiate between a volvulus involving ischemia (lack of blood flow leading to oxygen deprivation and tissue death) and a displacement or other type of colic where the blood supply is unaffected,” said Tyma. “Diagnostics may include palpation per rectum, passing a nasogastric tube to check for gastric reflux, abdominal ultrasound to evaluate the colon wall and vasculature positioning, and bloodwork to measure lactate levels (which can signal severe tissue damage and the need for urgent intervention) and assess overall systemic health.”

Tyma also stressed the need to carefully assess the reproductive tract in the immediate postpartum colicky mare to rule out life-threatening hemorrhage, the clinical signs of which can overlap with those of large colon volvulus.

Treating Large Colon Volvulus in Mares

If a veterinarian strongly suspects large colon volvulus, the mare will likely need emergency colic surgery. “The goals of surgery are to characterize the lesion, manually correct the volvulus, and assess bowel viability to guide surgery decisions,” said Tyma. The surgeon might also perform a colon resection (the damaged tissue can be removed, and the healthy ends of the intestine stitched back together) or colopexy (creating an adhesion to the body wall to prevent future displacements and torsions), she added.

Postoperative Care and Complications

Beyond the risks of surgery and general anesthesia, recovery from large colon volvulus surgery involves intensive care because these mares often become systemically compromised and can decline quickly. “The postoperative patient requires close monitoring with serial examinations, multimodal pain management, fluid therapy, broad-spectrum antimicrobials, digital cryotherapy (icing the legs), supportive care, and a gradual reintroduction of feed,” Tyma said.

She added that common postoperative complications can include endotoxemia (toxin release into the bloodstream), diarrhea, recurrent colic, surgical site infection, and the painful hoof condition laminitis. “Transitioning the accompanying foal to a nurse mare is often recommended to lessen the physiologic demand on mares early in the postpartum period.”

Prognosis for Large Colon Volvulus in Mares

“In the best of clinical scenarios, the short-term prognosis for large colon volvulus is excellent, with survival rates reported up to 90%,” Tyma said. “However, in studies representing a broad population with variable referral access (to a surgical facility), the short-term survival rate is just 71%, with long term survival dropping to less than 50% by one year postoperatively. This speaks to the importance of quick referral and management for successful outcomes.”

Sixty-seven percent of mares treated for large colon volvulus produce at least one foal postoperatively. “The risk of recurrence of large colon malposition (inclusive of both surgical correction of displacement and volvulus) is 15%, and, following two occurrences of volvulus, the recurrence rate jumps to 80%, which is significant,” Tyma said. “Mares with recurrent volvulus that are intended to continue as broodmares should be considered candidates for a prophylactic procedure (colopexy or large colon resection) to reduce the risk of recurrence.”

Take-Home Message

Large colon volvulus presents a true emergency in postpartum mares, demanding rapid diagnosis, aggressive treatment, and intensive postoperative care. Tyma emphasized the importance of prompt referral to a surgical facility and potentially prophylactic procedures such as colon resection or colopexy in high-risk mares to reduce the risk of recurrence. “Prognoses for survival and continuation of reproductive careers can be good to excellent but remain dependent upon quick recognition of the condition, immediate action, and appropriate surgical and postoperative management,” she said.

One of the defining features of pregnancy in horses is the lengthy gestation period, ranging from 320 to 360 days and averaging around 340 days. Generally speaking, if pregnancy loss in horses occurs after hormone-producing endometrial cups form in the uterus between 30 and 45 days of gestation, she cannot conceive again until the following year. Because the timing is so delicate and the stakes are often high, horse owners and veterinarians focus heavily on identifying and avoiding potential abortion triggers in mares.

Lauren Pasch, DVM, Dipl. ACT, CVA, of Rhinebeck Equine, in New York, reviewed the key risk factors for equine pregnancy loss at the 2025 Cavalcade Education Equine Reproduction Seminar, held on Jan. 8 in Red Hook, New York.

What Makes Equine Pregnancies Vulnerable

A long gestation period isn’t the only thing that makes mares vulnerable to complications. Pasch listed three other unique elements as innate risk factors for abortion:  

1. Long pre-implementation period. Horses have a unique type of placenta—called a diffuse, epitheliochorial placenta—and the embryo doesn’t fully implant until Days 40 to 42. This prolonged pre-implantation period makes the early stages of pregnancy particularly vulnerable.

2. Delicate maternal recognition process. The embryo moving around the uterus signals the mare’s uterus not to release prostaglandin, which would terminate the pregnancy.  Progesterone, produced by the corpus luteum (CL) initially and then by the fetal-placental unit, is essential for maintaining the pregnancy. Progesterone insufficiencies can lead to abortions.

3. Placental Inefficiency. “The horse’s placenta is remarkably thick and inefficient, with six layers of separation between the fetus and maternal blood supplies,” Pasch explained. “This makes the placenta highly susceptible to disruptions and insufficiencies.”

Risk Factors for Early-Term Pregnancy Loss in Mares

Most equine abortions occur before Day 42, when the primary CL remains the sole source of progesterone. Significant risk factors for pregnancy loss include:

• Previous abortion;
• Advanced maternal age;
• Systemic illness or pathology; and
• Chromosomal abnormalities.

“One area of growing interest is aneuploidy (an abnormal number of chromosomes) and chromosomal misalignment,” Pasch explained. “These chromosomal abnormalities are almost always lethal to the fetus.”

Risk Factors for Late-Term Pregnancy Loss in Horses

Once past the early, somewhat precarious stages of pregnancy, late-term abortions can still occur due to many complications, including:

• Umbilical cord torsions, which cut off blood flow to the fetus;
• Various congenital (present at birth) anomalies; and
• Placental insufficiency, often attributed to placentitis. Ascending bacterial placentitis—caused by infections moving up through the reproductive tract—accounts for most cases. “Evaluating a mare for placentitis involves rectal ultrasonography to measure the combined thickness of the uterus and placenta (CTUP),” Pasch said. “If elevated, the CTUP indicates inflammation because the placenta is thicker than normal.”

Infectious Causes of Pregnancy Loss in Mares

Last—but certainly not the least of broodmare owners’ concerns—are infectious causes of abortion. “Equine herpesvirus (EHV) and equine arteritis virus (EVA) are two significant ones,” Pasch said. Biosecurity measures and strategic immunization remain crucial for controlling the spread of these viruses.

Take-Home Message

Involuntary abortion in mares can be complicated, with many potential causes linked to the long, intricate nature of their gestation, and a range of external factors. By understanding, avoiding, and mitigating underlying risk factors, veterinarians and horse owners can minimize the devastating impact of equine pregnancy loss.

Preserving sperm quality during transport is paramount to equine breeding success. This principle applies whether using a fresh, cooled, or frozen sample. At the 2025 Cavalcade Education Equine Reproduction Seminar, held in Red Hook, New York,  Jan. 8, Alana King, DVM, Dipl. ACT, of Millbrook Equine Veterinary Clinic, in New York, shared the latest guidelines for the successful collection and transport of fresh, cooled semen.

Semen Collection Process in Horses

Obtaining semen for artificial insemination (AI) involves the stallion mounting a phantom mare or dummy, with the penis diverted into an artificial vagina (AV) to collect the semen. The AV setup is one of the most critical factors in successful semen collection. King highlighted the importance of adjusting the device’s internal temperature, pressure, and lubrication to each stallion’s preference. She recommended carefully recording the AV setup for each stallion to replicate it consistently.

Wash the stallion’s penis and sanitize equipment thoroughly to remove dirt and debris that could introduce bacteria and negatively impact semen quality. Along with a reliable teaser mare, King stressed the importance of having an experienced stallion handler present to ensure everyone’s safety.

Evaluating Equine Semen for Fertility

After collecting the semen sample, veterinarians evaluate it both grossly and under a microscope for quality—which translates to fertility—and pair it with an extender. King described the steps to measure volume, concentration, and total sperm count, noting these parameters can vary widely between stallions, but the total sperm count is the most important factor in determining fertility. “This number is generally 8 (billion) to 10 billion sperm per ejaculate, 1 (billion) to 2 billion of which is shipped to each mare,” she said.

Beyond sperm count, King also described the role of motility in assessing semen quality. “Progressive motility (sperm swimming in mostly straight lines or large circles) is a better predictor of fertility than total motility, because the latter counts sperm that move erratically without the ability to travel to and fertilize an egg.”

Role of Extenders in Horse Semen Transport

Semen extenders are specifically formulated preservative solutions that allow cooled sperm to survive transport and remain viable long enough for the mare to be artificially inseminated on arrival. King recommended conducting extender trials to determine the best option for each stallion because individuals’ semen can react differently to the antibiotics often contained in these extenders.

Maximizing Horse Semen Quality

To maximize semen fertility potential, King recommended:

• Before collecting semen for insemination, conduct clean-out ejaculations to avoid sperm degradation that can occur when semen is held in the epididymis for too long.
• Ensure proper lighting in the stallion’s stall to support optimal sperm production. Horses are long-day breeders (animals with reproductive cycles stimulated by an increase in daylight length).
• Consider supplements such as the antioxidant alpha (α)-lipoic acid and omega-3 fatty acids to improve sperm quality and motility.
• Centrifuge samples to remove seminal fluid that can be detrimental to stored semen.

Take-Home Message

With AI in horses, every extra step and hour lapsed between ejaculation and insemination has the potential to degrade semen quality. With the proper knowledge, equipment, and attention to detail, breeders can work alongside their veterinarians to consistently produce high-quality semen samples that maximize the chances of a successful conception, said King.

Mats Troedsson, DVM, PhD, Dipl. ACT, DECAR, of the University of Kentucky’s Maxwell H. Gluck Equine Research Center, in Lexington, Kentucky, addressed antimicrobial resistance (AMR) from a reproduction standpoint during a presentation at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida. 

In theriogenology, veterinarians use antibiotics to not only treat infections but also improve reproductive efficiency in the absence of illness. They often administer antibiotics in post­breeding intrauterine infusions, following natural mating, during embryo transfer, and in semen extenders for artificial insemination without evidence of infection. 

Breeding-induced or physiologic endometritis (inflammation of the endometrium, or uterine lining) is predominately triggered by the presence of sperm, not bacteria, in the uterus. The purpose of this inflammatory reaction is to eliminate excess sperm and any contaminating bacteria and inflammatory products to allow a hospitable environment for the embryo.  

Recent data show, however, that almost 30% of mares clear the uterus of inflammation within six hours of breeding/insemination/embryo transfer, and approximately 85% of broodmares are resistant to persistent endometritis. 

“This emphasizes how effective the uterine defense mechanism is,” said Troedsson. 

For mares that can’t clear the inflammation, we need to ask why, he said. 

“We have previously shown that these mares have impaired myometrial contractility in response to inflammation due to accumulation of nitric oxide in the uterus as well as an imbalance between pro- and anti-inflammatory cytokines in response to breeding,” said Troedsson. “Predisposing factors can also include poor perineal conformation.” 

When a mare fails to clear bacteria from the uterus, antibiotics are indicated and should be selected based on culture and sensitivity results. Treatment should continue for three to five days and can be combined with uterine lavage if fluid is present. Note that mares diagnosed with bacterial endometritis will not be bred in the same cycle, so there is time to wait for the laboratory results to guide treatment, he said. 

In the case of treatment failures, consider the presence of resistant or dormant bacteria located in the deeper layers of the endometrium or endometrial glands or the presence of biofilm. 

“bActivate is a sterile growth medium that activates dormant Streptococcus zooepidemicus after being instilled in the uterus,” said Troedsson. “The uterus can be cultured the day after activation and the mare treated if the culture is positive. If the culture is negative, the uterus is clear.” This also works for other bacteria, he noted. 

In the case of persistent infectious endometritis that doesn’t respond to treatment, biofilms that evade both the immune system and antibiotics could be to blame.  

“Bacteria on the surface of the biofilm are exposed to sufficient concentrations of antibiotics, but reduced diffusion through the biofilm matrix leads to decreased concentration of antimicrobials within the biofilm community,” he explained. “This provides an excellent opportunity for bacteria to develop AMR. Further, genetic alterations associated with AMR are easily transmitted between bacteria in the biofilm, contributing to AMR.” 

To treat these infections, vets must first diagnose or suspect a biofilm, then break it down. “Biofilms are very difficult to diagnose in the field,” Troedsson said. “One potential way of diagnosing biofilms is to identify proteins or lipids specific to biofilms. If those molecules can be consistently recovered from mares with biofilms, an in vivo assay can be developed.” 

While veterinarians must treat endometritis using antibiotic therapy, Troedsson ­recommends treating breeding-induced endometritis with ecbolics, lavage, and possibly immune modulators, such as bacterial cell wall fractions (Settle), platelet-rich plasma, dexamethasone, or lactoferrin. 

“Antibiotics are not the first choice,” he stressed. “We know it is semen, not bacteria, causing the inflammation and subsequent uterine fluid.” 

Troedsson concluded by stating that while antimicrobials are valuable in equine reproduction for proven infections, using antibiotics to assist reproductive efficiency in horses with no health and well-being issues poses a challenge to equine practitioners. 

“We need alternatives to antibiotics, and decisions should be made based on scientific data rather than traditions and habits, such as routinely using antibiotics to flush mares 24 hours post-mating,” he said. 

Get to the root cause of aggression and pursue appropriate training to help keep horses and humans safe

The 7-year-old Warmblood was a show jumping superstar—or at least, he used to be, back when riders could get on him. The 17-hand horse became so dangerous his owners were losing hope. That’s when they sent him to the Australian equitation-science-based horse trainer Andy Booth, now based in Chamadelle, France.

“You couldn’t even get him out of the stall without getting kicked,” Booth recalls. The stallion threatened anyone who approached the door. If you managed to get a lead on him, he’d rear to vertical, striking out incessantly toward the handler. In the rare event handlers could get him saddled, he’d buck and twist to throw the rider high and far.

We’ve asked experts to find out why horses display aggression and how to manage them—whether the label is accurate or not—for the safety and welfare of both species.

Normal Aggression in Horses

Horses showing aggression toward other horses—but not other species—are likely just displaying their normal species-specific behavior, says Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute for Equine Science, in Neustadt, Germany.

Still, domestic horses usually limit aggression to nonviolent threats, says Alice Ruet, PhD, welfare science engineer at the French Institute of the Horse and Equitation (IFCE), in Saumur, France. If you provide enough space—whether in the field or under saddle—horses generally work out aggressive encounters via body language.

“Being highly aggressive is probably not biologically adaptive, as horses would waste energy fighting when they could be resolving issues through subtle behaviors instead,” explains Janne Winther Christensen, PhD, associate professor in the Department of Animal and Veterinary Sciences at Aarhus University, in Tjele, Denmark.

Horse Aggression Toward People

Today’s domestic horses reflect five millenia of selective breeding to avoid aggression. In fact, tamability was likely the first trait people targeted when domesticating horses around 3000 B.C., says Ludovic Orlando, PhD, director at the Center for Anthropobiology and Genomics of Toulouse, in France.

His team recently noted a rapid generational drop in the presence of ZFPM1—a gene associated with aggression—in ancient bones at horses’ earliest domestication sites, in Kazakhstan. That drop occurred well before breeding for height, muscle mass, speed, or rideability. “One way to start the animal domestication process is to have the behavior under control,” Orlando says.

Still, many other genes could be linked to aggression, says Ruet. “Certain personalities might predispose horses to becoming aggressive when poor welfare triggers it,” she says.

Some such genes might linger because they coincide with desirable traits, Aurich explains. “A racehorse probably needs some aggressive character components to become a front-runner, and a cutting horse needs some aggressive behavior versus cattle,” she says. Breeders generally know which lines produce more aggressive horses, she adds.

A genetic propensity for aggression might even lie dormant “within the telos of all horses,” says Andrew McLean, BSc, PhD, Dipl. Ed, owner and director of the Australian Equine Behaviour Centre, in Moorooduc, Victoria. This tendency could be exacerbated by other unknown genetic factors and sex hormones such as testosterone, he says.

Evidence-based management and training styles reduce the risk of revealing latent aggression in horses, McLean says.

What Brings Out Horse Aggression?

Aurich and Ruet agree that interactions between horses appear to have an important role in stirring up aggression. Orphaned, bottle-fed foals and stallions raised away from a bachelor herd face a higher risk of developing aggression. “Being raised in a group apparently helps train their social skills—
including towards humans,” Aurich says.

Ruet says pain is another critical factor that, as in humans, can lead to aggression, even if the horse is simply anticipating it.

Improper management can also encourage aggression. In fact, overlooking horses’ inherent needs can “result in disaster,” Aurich says. This is more likely to manifest in horses that tend to have a stronger fight-or-flight response, she adds.

Managers should aim to reduce horses’ stress and frustration, providing access to friends, forage, and freedom—the classic “3 Fs” of horsemanship, Ruet says. In fact, she found that show horses kept in stalls without access to the 3 Fs became aggressive—or progressively more aggressive—toward people over two years.

Boredom might also encourage aggression, especially in stallions, Aurich adds.

Trainers, meanwhile, should adhere to scientific guidelines based on horses’ abilities to learn, says McLean. Otherwise, methods can cause confusion and frustration.

Is Horse Aggression Innate or Learned?

There’s a difference between truly aggressive horses and horses that have picked up aggressive behavior due to the benefits it provides. Both situations are dangerous and can be difficult to fix, but it’s crucial to know the difference.

Truly aggressive horses act out of negative emotions—roughly equivalent to human anger, says Ruet. In her research she’s even shown that aggressive horses strike their feet harder against the ground under saddle than nonaggressive horses do—like angry humans stomping around. These horses clamp their jaws and flare their nostrils, often remaining highly agitated even after an aggressive act, she explains.

Horses that have learned aggression, however, might appear angry without the accompanying negative emotions. They could have figured out, for example, that threatening to bite makes people move away, says Booth. Or they know leg cues disappear when they buck or rear. These horses often seem calm after acting aggressive.

Let’s go back to that show jumper as an example. After watching him rear and strike out, Booth says he realized the horse wasn’t going for the handler’s head; instead, he was trying to catch the lead between his forelimbs. The handler would always release the pressure, and the horse would walk calmly away to graze. “He’s figured out exactly how to get that pressure release,” he says.

Angelo Telatin, PhD, associate professor of equine studies at Delaware Valley University, in Doylestown, Pennsylvania, says aggression often develops as a learned defense from to improper training. “They’re aware that they can move you,” he says. “If the horse is truly aggressive—with the power it has—you’d be dead.”

Many aggressive horses have not been trained with a method called shaping—learning in small, incremental steps. “If you don’t shape before applying leg pressure for the first time, some horses get stiff in the body; some turn around and bite the leg; some act like it’s flies, and they kick,” Telatin says. Applying stronger pressure usually just leads to more aggression. “Some horses dump you or buck you off, or rear and back up, or bite your leg hard.”

A similar problem occurs with whip use on the ground, Telatin adds. “As soon as horses come out with the fight or flight behavior, they see you back off with the whip or longe line,” he says. “So you’re actually shaping this attack behavior.”

People often confuse learned equine aggression with disrespect—which is beyond a horse’s cognitive abilities—or dominance, Telatin says.

Booth agrees: “He’s not trying to dominate you. He’s trying to rip your arms off so you stop annoying him.”

Regardless of whether true or learned, all aggression probably has its roots in a welfare issue, insists Ruet.

First Up: Relief and Safety

Our sources emphasize that aggression demands immediate attention and effective management.

Instead of labeling a horse as mean, consider his history. “Horses express poor welfare in a variety of ways, and aggression is one of them,” says Ruet.

With stallions, handlers can use enrichment (such as feed balls or toys) to help pass the time—as well as training sessions to stimulate their minds, Aurich says. Critically, stallions need a lot of social contact beyond mere breeding. Handlers should try to provide contact over safe barriers or even a trans-species companion such as a goat.

Aurich recommends veterinarians find and treat any back, foot, or leg pain, gastric ulcers, dental issues, or other sources of pain. “It can be very difficult to identify the cause, but a workup is super important,” she says. “This may take time and a lot of patience.”

Drugs can serve as a last effort to manage aggressive horses, Aurich says. Certain calming agents and pheromones might temporarily reduce aggression, but no current research confirms their effectiveness for this purpose. Analgesics or anti-inflammatories could make some horses less aggressive if the drugs relieve their pain. But even if drugs help, only consider them temporary solutions while working to confirm and resolve the underlying problems, she says.

Meanwhile, people need to focus on minimizing their own safety risks, our sources say. Fence aggressive horses away from high-traffic areas. Use muzzles if necessary.Wear protective equipment such as helmets, vests, hard-toed boots, and even shin guards when working with these horses.

Next: Shift to Positive Associations

After resolving any health and welfare issues, restart the horse-human relationship with patience and positive associations.

“Just get out there and spend some time with them without working them,” Ruet says. This doesn’t mean horses don’t like to work—and, in fact, work can be a positive experience. “But if the only time horses see humans is because the humans want them to work, that’s not ideal,” she says. Aim for quiet, comfortable encounters with food rewards and mentally stimulating experiences.

Lasting Behavior Change

When the horse’s perception of humans improves, skilled trainers can work in teams to gently retrain the horse.

For Booth, trainers must always “make the right response comfortable and the wrong response uncomfortable,” he says. He quickly retrained the jumper that always presented his hindquarters to the stall door by waving a small flag in front of the door until the horse turned; when the horse approached the door, Booth gave him a treat through the bars. Within a few sessions, he could safely open the door and halter the horse. He would then lead the stallion out to graze, creating and maintaining a positive association with the stall door opening.

Telatin retrained a mare that would bite anyone coming into her stall by clicker-training her to play with a ball instead. “Then you could halter her or do whatever you wanted,” he explains.

People can use their elbows to block biting horses in swift movements, say Telatin and Booth. Elbow pads can be very helpful here, Booth adds. For bucking horses, you can start retraining with a dummy tied to the saddle—but eventually a skilled rider needs to get on, stay on, and ride out the bucking until the horse offers the right response—calmness. Importantly, riders must release pressure at the calm moment to reinforce the correct response.

Still, retraining aggressive horses can be particularly dangerous—especially because they tend to intensify aggressive responses before trying other behaviors, Booth says.

The Spontaneous Return Factor

Once horses have learned aggression works in their favor, it’s difficult to make that behavior disappear—despite the best science-based retraining methods. “The behavior can always spontaneously reappear, even years later,” Booth says.

Sometimes such horses can be rehomed with someone who understands the risks and knows how to avoid them, he says. In certain cases, though, the most humane decision might be retirement or euthanasia.

Take-Home Message

Aggressive horses are usually made, not born, and many aggressive behaviors have their roots in welfare issues. It can be difficult to de-train aggression because the behavior is so effective in removing pressure. Handlers should use science-based management and training to avoid pain, frustration, and other welfare problems that might lead to aggressive behavior. If such aggression does develop, take it seriously from the beginning by looking for welfare issues and working with a science-savvy professional to retrain the behavior before it sets in for good.

This article is from the Spring 2025 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Q: How can I prevent nutritional deficiencies without causing developmental issues in a growing foal?

A: Developmental orthopedic disease (DOD) is a common concern in young horses, referring to a group of conditions where skeletal growth occurs abnormally. While nutritional mismanagement can be a factor, proper nutrition can help manage the risk of developmental issues.

Feeding young horses requires careful planning, starting before birth. Ensuring the mare’s optimal nutrition during pregnancy and lactation is essential for fetal development and milk quality. Once born, foals should begin consuming concentrates at around 28 days old; a good rule of thumb is 1 pound of feed per month of age per day. Feeding with progressive and consistent increases will encourage steady growth curves associated with optimal skeletal development. Erratic changes, feeding an improper concentrate, offering it free-choice, or making sudden changes to the amount of concentrate, can result in the unpredictable growth curves that are the hallmarks of DOD development. You can design your feeding program to support rapid versus moderate versus slow growth rates depending on the goals for that foal, but make these decisions with few changes occurring during the early growth period.

It’s a misconception that excess calories or protein alone causes DOD. Instead, imbalances in these and other nutrients have been linked to abnormal growth. Think of calories as the fuel for growth and nutrients (amino acids, vitamins, and minerals) as the structural building blocks. Too much fuel and too few building blocks will create rapid, incorrect growth. Too little fuel and you will be missing out on some genetic potential for growth, which could hinder muscle development. In addition to energy and protein, other nutrients need to be maintained in certain ratios to ensure optimal utilization. Calcium and phosphorus are classic examples of nutrients that should remain balanced to a ratio of no less than 1:1 (2:1 being optimal). Similarly, zinc and copper must be balanced in a ratio of around 4:1 in a complete diet. 

A simple way to stay on track is to:

1. Feed to suitable body condition, which is when ribs are not or just barely seen and easily felt, and
2. Use only feeds appropriate for growth. Look for items designated for mare and foal, growth, or all life stages. This means the nutrients are balanced for young horses, and the balance between calories and nutrients is appropriate. 

The key difference between growth and performance feed is that a performance feed for an adult horse has a higher ratio of calories to nutrients, meant to support working horses but not adding structural growth. Growth feeds are available at all calorie levels, so the exact choice of concentrate will be dictated by the individual’s metabolism and forage intake and quality. Ration-balancing feeds are a good option to provide nutrients if your horse receives sufficient calories from forage alone. A young horse should generally stay on a growth-appropriate program until 2 years old, sometimes longer for particularly late-maturing breeds such as some warmblood or draft breeds.

Do you have an equine nutrition question?

Contagious equine metritis (CEM) is a highly contagious venereal disease affecting horses, with potentially severe implications for breeding operations. Caused by the bacterium Taylorella equigenitalis, CEM primarily affects mares, causing vaginal discharge, temporary infertility, and, in some cases, long-term carrier states. Stallions, while asymptomatic, can be silent carriers capable of spreading the disease through natural breeding or artificial insemination.

CEM Transmission and Risks in Horses

Contagious equine metritis spreads in three primary ways:

• Between a mare and stallion during live-cover breeding.
• From stallion to mare via contaminated semen used in artificial insemination.
• From stallion to stallion through shared breeding equipment.

Mares can sometimes clear the infection on their own, but many become chronic carriers, maintaining the bacteria in their reproductive tract and serving as a long-term source of transmission. Stallions, unless diagnosed and treated, can transmit the bacteria indefinitely.

CEM Outbreaks in the U.S.

Although the United States has been considered CEM-free since the mid-1980s, multiple outbreaks have occurred. Six reported incidents have emerged since 2006, with three classified as full-scale outbreaks. The most significant outbreak, spanning 2008 to 2010, involved 23 stallions and five mares. More than 1,000 exposed horses across 48 states were tested, with the infection traced to a stallion imported from a CEM-affected country in 2000.

Between May 2024 and March 2025, the USDA confirmed 52 cases of CEM in an outbreak associated with transmission at a single farm in Florida. The outbreak was first identified when a pony stallion on the farm infected a pony mare that subsequently showed clinical signs of CEM and tested positive for T. equigenitalis. These two animals and one other pony stallion were the only breeding animals involved in the case—the other 49 were geldings who acquired the infection through sheath-cleaning practices on the index farm. None of the geldings arrived at the farm as stallions; current epidemiology (the study of disease, health, and their determinants in populations) indicates one must have arrived infected. In addition to the 52 confirmed cases, officials said at least another 140 were potentially exposed. This is the first finding of extensive gelding-to-gelding spread of T. equigenitalis through inadequate biosecurity during sheath-cleaning practices in the U.S.

Prevention and Biosecurity Measures

To mitigate CEM risks veterinarians recommend the following precautions for breeding operations:

• Adhering to the American Association of Equine Practitioners’ biosecurity guidelines for venereal disease prevention.
• Regularly testing active breeding stallions before the breeding season using direct swab culture for T. equigenitalis. Testing requires collecting swab samples from multiple sites on a stallion’s genitalia and submitting them to a CEM-approved laboratory.

Even a single negative test provides valuable insight into a stallion’s CEM status. However, veterinarians encourage multiple tests to ensure accuracy and prevent undetected carriers from spreading the disease.

To reduce the risk of CEM spread to geldings, experts recommend:

• Wear disposable gloves and change gloves between geldings.
• Use a disposable bucket liner in the wash bucket and paper towels or disposable rags that will not be shared between geldings.
• Avoid using a hose that can become contaminated during handling.

The Stakes for Stallion Owners

The potential financial and horse-health consequences of a CEM outbreak are significant. Beyond the health risks to breeding stock, outbreaks can lead to quarantine measures, disruptions in breeding schedules, increased costs to treat outbreaks, and disruption in the international movement of U.S. horses and semen/embryos.

Ensuring compliance with testing and biosecurity measures is not just about protecting individual breeding programs—it is a collective effort to safeguard the equine industry. Stallion owners, veterinarians, and breeding facility managers play a vital role in preventing future outbreaks and maintaining the country’s CEM-free status.

By taking proactive steps, the equine industry can continue thriving while minimizing the risks associated with this serious but preventable disease.

Editor’s Note: This article has been expert reviewed by Angela Pelzel-McCluskey, DVM, MS, equine epidemiologist at the USDA for accuracy.

10 emergencies to watch for in the hours after your mare foals

Phew! That baby is born. The past 11 months of waiting, monitoring, and hoping have ended, and that beautiful wet foal is now on the ground wondering what on earth just happened to her. Your mare, meanwhile, is back on her feet—curious and wondrous about that squirmy little ragamuffin that just came out of her.

It might be tempting to assume that all is well, and you can finally get your own much-needed deep sleep. Unfortunately, though, your bed will have to wait—you’ve only completed part of the complex process of successful foaling. The next few hours and days will be critical in determining the future physical and mental health of your mare and her newborn foal, says Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute for Equine Science, in Neustadt, Germany.

So get your foaling night blankets and hot thermoses of coffee—and brush up on your smartphone stopwatch features—as you keep a watchful eye out for these 10 red flags in the post-foaling period.

1. Foaling Passes the 20-Minute and/or 45-Minute Mark.

Careful breeders have their stopwatch apps open before they even see the foal, Aurich says. “At the moment the placenta breaks, and the birth process is starting, you should really start your watch,” she explains.

If the foal isn’t delivered within 20 minutes, there’s certainly a problem that merits investigation, she says. If handlers have had training in managing difficult births, they can try to help resolve basic problems like a stuck shoulder or flexed knee. Otherwise, they should call a veterinarian immediately.

Regardless, foals should be born within 45 minutes, Aurich cautions. Longer than that, and the foal is more likely to suffer from health issues such as general infections or neurological disorders due to lack of oxygen.

Good prenatal care can help prevent or at least forewarn handlers about issues that could complicate foaling, so they can be prepared, says Quinn Gavaga, DVM, of Charles Ranch Equine, in Ashcroft, British Columbia, Canada. “The health of the mare cannot be overstated,” he says.

2. The Placenta is Late—or Early—and/or Isn’t Y-Shaped.

Mares should deliver the placenta within three hours of birth, says Aurich. Otherwise, a retained placenta could cause uterine infection and the resorption of endotoxins, provoking sepsis (a whole-body reaction to bacterial infection) in the mare, which could also lead to laminitis. This “very dangerous and life-threatening” issue can usually be quickly averted with oxytocin infusions that make the uterus contract and expel the placenta.

But early placentas are red flags, too, she says. If the placenta and foal come out together, or if the placenta emerges before the umbilical cord is torn because the mare has gotten up, it was probably infected (evident as placentitis, or inflammation of the placenta). “An early placenta is always an alarm,” Aurich says. “It means there was a problem already before the foal was born and that the foal was most likely infected in the uterus.” These foals develop sepsis, requiring aggressive treatment.

Mares with placentitis could also have a red bag delivery. This condition occurs when the placenta separates prematurely from the uterine lining and—rather than normal translucent white or yellow membranes—you’ll see the bright red, velvety intact chorioallantois (the outermost layer of the placenta) at the vulvar lips. In these emergency cases the placenta must be opened immediately and the foal pulled out to halt asphyxiation.

After every foaling, handlers should lay the placenta out flat and ensure it’s complete, in its typical Y-shaped form, she adds. An incomplete placenta means a piece has remained inside the mare, which poses the same risks as retaining the entire placenta.

Handlers can also weigh the placenta while waiting for the veterinarian. It should weigh 10-12% of the foal’s weight; if the figure is less or more, it signifies a problem with the placenta.

Be sure to save the placenta in a plastic bag or bucket in a cool place for several hours because it could offer important clues if problems arise later, Aurich says.

3. The Foal Isn’t Standing Within One Hour.

Ideally, foals stand very quickly after birth—often within a matter of minutes, Aurich says. At the very latest, they should stand within an hour.

Some foals squirm and struggle to stand but just can’t succeed. Problems that could cause this range from contracted tendons and neonatal encephalopathy to sepsis.

Foals that don’t even try to stand within an hour are probably ill and need urgent veterinary care.

“When something goes wrong with foals, it usually happens pretty quickly—so don’t wait for it to get better on its own,” Gavaga warns. “It almost never does.”

4. The Colostrum Doesn’t Pass the Home Brix Test.

Before mares foal, owners should purchase a Brix refractometer, Aurich says. This instrument—designed primarily for the food and beverage industry—also serves as an excellent breeding farm tool to test for density or specific gravity of colostrum. (Colostrum with high immunoglobulin levels has a greater density and, thus, a higher specific gravity.) “It’s a very easy and really cheap way to check your colostrum quality right away,” she says.

Handlers should squeeze a small drop of colostrum from the mare’s udder—ideally, just after the foal is born—and place it on the refractometer prism. If the Brix value is at least 25%, that means the colostrum quality is good. If it’s above 30%, it’s very good. However, if the Brix value is below 25%—and especially if it’s lower than 20%—“then you know there aren’t enough antibodies for your foal,” Aurich says. “You have to call your vet to get frozen colostrum from a broodmare farm” or the foal will likely need an intravenous (IV) plasma transfusion.

5. The Foal Isn’t Nursing Within 2 Hours.

Among all the time-sensitive boxes to check, the intake of colostrum—the mare’s antibody-rich “first milk”—probably ranks No. 1 in importance, Gavaga says. Foals that fail to consume enough colostrum within the first few hours lack the antibodies that protect them from even the most common pathogens, he explains. That means they could easily fall sick, creating a domino effect of lingering health problems, including sepsis. Without rapid veterinary help, they’re likely to die within days. Sepsis is the leading cause of mortality in newborn foals, adds Aurich.

Healthy foals usually nurse within one hour of birth, but some can take a little longer before they start searching for the mare’s udder. If they’ve reached two hours without nursing, they absolutely need human intervention; call your veterinarian immediately.

After informing their veterinarians of the foal’s missed milestone, handlers should milk the mare themselves, Aurich says. This involves gently drawing on her teats and collecting the colostrum in a clean bottle designed for human babies. Handlers should be careful not to spill or waste the colostrum. It’s best to wait for veterinary assistance before offering it to the foal: Importantly, foals need to suckle and swallow on their own without being forced or having milk poured into their mouths, she adds.

6. The Foal Isn’t Getting Up to Nurse Every Half Hour, Suckles the Wrong Thing, or Gets ‘Milk Head.’

Foals usually lie down to rest after nursing. “But then they should get up after a short period, not longer than 30 minutes, and go again,” Aurich says. They should also act alert and interested. “That’s very important. If they’re not doing that, then something is happening. Something is wrong.”

The foal shouldn’t have milk on his neck, ears, or face, either, Aurich explains. “Milk-head” occurs when the foal approaches the udder but fails to latch on to the teat, and the mare’s body releases the milk in response to the foal’s contact, spraying milk onto the foal’s head. “It means the foal isn’t nursing correctly and isn’t getting enough nourishment,” she says.

Milk-head foals do not need “training” to nurse correctly, says Aurich. They need veterinary care. “You have to check the foal because it most certainly has a problem,” she says. It’s not that the foal doesn’t know how to nurse but, rather, she gets disinterested or too tired to drink once the milk is flowing. “In most cases, this is a sign that the foal is getting sick.”

But it might also be a sign the foal was born with a slightly premature endocrine system, Aurich adds. Before birth, foals usually produce progestogen, then shortly before the mare goes into labor, they switch to producing cortisol instead. In certain cases foals that appear fully mature might still be producing progestogen—which actually has a sedative effect, she explains. Therefore, they don’t adapt well to life outside the uterus, they might suckle incorrectly and get milk-head, or they might even try to suckle the mare’s legs or the barn wall.

Watching suckling behavior is the most reliable way to assess the health of newborn foals, because their body temperature and other vital signs are still naturally fluctuating, Aurich adds. “Taking temperature isn’t helpful,” she says. “But looking for normal behavior is.”

7. The Foal Is Retaining Meconium.

The foal’s digestive system needs to clear the dark, tarry contents it accumulated during gestation, known as meconium. Currently, the recommended practice is to administer one or two enemas at birth to avert meconium retention.

Foals that struggle to pass meconium tend to strain, lifting their tails and often standing as if they want to urinate, but to no avail. As time goes on, they can show signs of foal colic—acting restless and lying down as if they’re trying to keep pressure off the abdomen. In addition to the obvious welfare concerns, meconium constipation can cause foals to stop nursing—which prevents them from consuming the colostrum and nourishment they need to stay healthy.

Foals should poop approximately every half-hour for the first hours until all the meconium has passed, and yellowish milk feces appear. However, foals younger than 3 or 4 days old should never have diarrhea, Aurich adds. If they do, this is most likely septic diarrhea.

The first urine comes later. “If they are drinking—and drinking enough—they will certainly start urinating within 12 hours or so,” Aurich says. Colts typically urinate within eight to 10 hours, whereas fillies start within 12-14 hours.

Notably, owners should not assume an empty udder means the mare isn’t producing enough milk, Aurich adds. As long as the foal is nursing regularly, the udders always appear empty even though they might be producing abundant quantities of milk.

8. The Mare Seems Disinterested, Colicky, or Sick, or Has Bloody Manure or Urine.

Healthy mares show an interest in eating hay and pay close attention to their foals, Aurich says. They should be passing feces and urine within five or six hours of foaling.

Sick mares might act lethargic or depressed and could appear sweaty. Rectal temperatures above 38.5 C/101.5 For a resting heart rate higher than 50 beats per minute is cause for alarm. In a septic mare laminitis can start quickly, so handlers should check for signs of sore feet.

While mares might have mild abdominal discomfort for a few hours after foaling, they should not experience significant levels of pain, Aurich says. Importantly, pain should improve—not worsen—over time. Handlers should be concerned if the mare is getting up and down frequently, rolling and/or thrashing, or showing increasingly more severe facial expressions of pain such as tightening around the eyes, clenching the jaws, or pursing the lips. Blood in the urine or feces is another critical red flag.

Such signs could point to serious issues such as uterine prolapse, a retained placenta, damaged intestine, uterine rupture, or a burst artery with bleeding into the abdominal cavity. “These are real emergencies that have to be attended by a veterinarian,” she says. Haul the mare and foal to a clinic immediately if a vet cannot come right away.

“Better to transport her with hope of saving her, than just waiting at home until she’s dead,” Aurich adds.

9. The Foal’s IgG Levels and/or WBCs are Out of Range.

Veterinarians recommend testing every newborn foal’s blood in the first six to eight hours of life to check IgG concentrations.

An IgG reading under 8 grams per liter is a critical red flag showing the foal did not receive a sufficient transfer of antibodies. A white blood cell (WBC) reading outside the normal range of 5,500-12,000 cells suggests the beginning of sepsis.

Remember that 85% of antibodies from colostrum is transferred in those first eight hours. So, if you’ve tested within that window and the IgG is low, you still have time to feed colostrum (whether from the dam or a donor) nasogastrically and get adequate transfer; the foal’s intestinal tract cannot absorb these vital antibodies past 24 hours.

Beyond that eight-hour time frame veterinarians can provide the foal antibodies through IV plasma infusion.

As for other measurements, a particularly low or very high WBC count reveals an immune system reaction, our sources say. Practitioners can also run a serum amyloid A (SAA) test. The reading should be under 100-150 to verify the absence of bacterial activation of the acute-phase protein SAA, which is produced by the liver.

10. The Foal and Mare are More Interested in Anyone Besides Each Other.

Mare-foal bonding is critical for good physical and mental development of the foal as well as the welfare of both animals.

While handlers should not hesitate to care for their foals, especially when they need help, human interactions with foals should remain as minimal as realistically possible, Gavaga says. “Concentrate on the mare and make her feel as relaxed as you can,” he says. “Do what you need to help, but don’t try and force a bond with you and the foal. Respect the mare’s relationship with her foal.”

Red Flag? Do Not Wait.

If you see any of these red flags, contact your veterinarian immediately. “I don’t think people miss the signs that often,” Gavaga says, based on his own clinical experience. “I think owners wait too long to react.”

Post-foaling is certainly not the time for taking the wait-and-see approach, or to let nature work things out, Aurich adds. “Nature can be cruel,” she says. “Nature helping means the wolf or the lion comes for the weak foals that can’t get up and run away.”

For optimal post-foaling success, breeders should maintain a very good relationship with their veterinarians, Gavaga says. They will often then go above and beyond in supporting their clients in all the phases of horse breeding.

Take-Home Message

Mares and foals can appear healthy at foaling but quickly go downhill if they develop complications in the post-foaling period. Knowing the red flags and acting quickly can make a dramatic difference in the outcome of these scary situations, our sources say. “You can’t be prepared for every scenario,” Gavaga says. “But you can try to get as much knowledge as you can beforehand to be prepared for the main problems that can happen.”

Your horse’s nutritional requirements depend on his life stage and individual needs

All horses need the same essential nutrients—water for cellular, tissue, and organ function, carbohydrates and fats to fuel body functions, protein to build and repair tissues, and certain vitamins and minerals to promote and maintain normal physiological function. Feeding an appropriate diet, however, is not just a matter of tossing them some hay, grain, and supplements. Creating a diet for your horse involves a targeted plan that allows him to use nutrients more efficiently.

To figure out what your horse needs, realize that horses are grazers designed to eat little and often, says Amy Parker, MS, equine nutritionist and technical services manager at McCauley’s, in Versailles, Kentucky. Their natural diet is mainly grass, which has a high roughage content. So, their diet as domesticated animals should be predominantly fiber-based— whether it’s grass, hay, haylage, a hay replacement, or a combination thereof—to mimic their natural feeding pattern.

Parker says the right diet for your horse must reflect his individual needs, taking into consideration factors such as age, weight, body type and condition, health, level of work, and physiological state (e.g., growing, pregnant, lactating). Time of year and weather conditions are also important to consider when formulating the appropriate diet. For example, if the horse gets most of his nutrition by grazing good-quality pasture, then he needs alternative feed sources (i.e., hay) when grass isn’t available. “All of this information provides the foundation to develop the whole diet—forage and feed components,” says Parker.

The National Research Council’s Nutrient Requirements of Horses is the standard guide for feeding horses. Although this text provides much more information than the average horse owner might need, it also offers basic guidelines for energy, protein, and some macromineral (i.e., calcium, phosphorus) amounts based on mature horse body weight. “Once we have met these needs, then the rest is usually okay,” says Shannon Pratt-Phillips, PhD, professor of equine nutrition and physiology at North Carolina State University, in Raleigh.

From Foal to Juvenile

Horses have different nutritional needs depending on their stage of physical maturity. In general, provided a lactating mare is in good body condition and on a balanced diet, we don’t have to worry about feeding the foal because the mare’s milk includes all the nutrients he needs, says Parker. Rather, we consider and select the proper diet when the foal transitions to a weanling and begins consuming solid feed. Young, growing horses need extra energy, protein, and the correct amount of minerals, such as calcium and phosphorus for proper bone and tissue development.

Digestible energy intake greatly influences a young horse’s growth rate, says Pratt-Phillips. In general, the more energy fed, the faster the growth. She says you can adjust diets to accelerate growth in horses earmarked for sale or competition as well as slow growth rates for horses intended to be marketed at a later stage of maturity.

Horses 4 to 6 months of age are defined as weanlings, whereas those 12 to 18 months of age are considered yearlings. Depending on the average daily weight gain you desire for your growing horse, first choose the appropriate forage type to feed. We know pasture alone typically doesn’t meet a growing horse’s nutrient needs, says Laurie Lawrence, PhD, professor of equine nutrition at the University of Kentucky (UK), in Lexington. Further, season affects a pasture’s nutrient content. For the growing season of most legume/grass pastures, the energy and protein content is highest in spring and fall and lowest during the summer.

Lawrence says choosing a hay to match the horse’s needs is a good way to ensure adequate nutrition from the forage. Hay has the highest nutrient value (composition) when harvested in its immature state of growth. Legume hay (alfalfa or clover) is higher in digestible energy, protein, and calcium than grass hay (e.g., timothy or orchardgrass). So, if you are selecting hay, look for the stage of maturity to be between pre-bloom and mid-bloom (prior to the plant flowering) for legumes and pre-head (prior to the plant producing a seed head) for grasses.

Growing horses’ hay consumption varies depending on the hay quality (related to the hay’s maturity at the time of harvest) but usually ranges from 8 to 15 pounds per day for weanlings and 15 to 25 pounds per day for yearlings.

Because feeding growing horses is a balancing act where you don’t want to provide excess or inadequate dietary energy or protein, Lawrence suggests keeping the diet proportions at 30% forage to 70% concentrate for weanlings and between 55/45 and 50/50 forage to concentrate for yearlings.

Average Adult Horses

Mature idle horses can do well on good-quality all-forage (pasture or hay) diets with vitamin and mineral support in the form of a ration balancer, says Parker.

Base forage selection on the type necessary to meet nutrient requirements. For a mature idle horse, this is typically an early to late-head grass hay.

Senior Considerations

Aged or senior horses (18+ years) have additional dietary considerations. They are less able to process and absorb nutrients from feed and have a less efficient microbial population in the hindgut, says Pratt-Phillips. These horses need high- quality pasture and hay with at least a 60% legume content. Senior horses might also develop metabolic problems (such as pituitary pars intermedia dysfunction) that require a specialized diet low in soluble carbohydrates, including warm-season hays that are naturally low in insoluble sugars, such as teff or some species of Bermudagrass.

Pregnant and Lactating Mares

Broodmares’ digestible energy, protein, and macromineral (primarily calcium and phosphorus) requirements jump during late pregnancy (last trimester) and lactation (foaling to three months). For these horses to maintain a healthy body condition, Parker recommends selecting feed that complements the forage to meet the nutrient requirements. For instance, if you feed your pregnant or lactating mare legume/grass hay, add a concentrate feed with moderate protein (12-14%) that is fortified to meet her vitamin and mineral requirements. If you feed a straight grass hay, you’ll need to provide a higher-protein feed. Lawrence recommends offering early to mid-bloom stage legume hays and pre-head to early-head stage grass hays. In general, pregnant mares in late gestation and early lactation consume 70-80% and 50-60%, respectively, of their diet in forage.

Calculating Correct Amounts

Nutritionists generally base their feed recommendations on amounts per kilogram or pound of mature body weight. So your horse’s weight and body condition are essential pieces of information. A livestock scale will tell you the precise body weight of your horse, allowing you to make better decisions about how much feed to provide. You can also make body weight estimations using a weight tape or the body weight formula:

Body weight (lb) = heart girth (in)2 x body length (in)/330

Parker also recommends using the Henneke body condition scoring system (TheHorse.com/164978) on your horse. This system allows the user to evaluate the amount of fat deposition in various body regions, which can guide how much to feed.

Work increases digestible energy needs. The increase ranges from 25 to 50% above maintenance levels with horses in light to moderate work (working five hours or less per week) to 100% above maintenance in horses in heavy work (e.g., upper-level eventing, racing, endurance). Environmental conditions, such as heat and humidity, also affect horses’ dietary requirements due to replacement losses of minerals in sweat.

Choosing Forage Types

You can add forage besides pasture or baled hay to your horse’s diet. These include hay cubes, pelleted hay, chopped hay, dehydrated hay, and haylage. Each poses advantages and some disadvantages, says Parker, but all must be fed based on the product’s weight.

A variety of forage mixtures are avail-able as hay cubes, which are usually 2-by- 2 inches, and can be fed as a substitute for long-stem hay. Horses that waste a portion of their long-stem hay might benefit from consuming a cubed hay, says Robert Coleman, PhD, associate professor at UK. Cubed hay is cut uniformly, thus eliminating sorting issues. Another benefit of hay cubes is you can weigh and store them easily. Cubes are usually made from forage that was cut at an early stage of maturity, giving them a guaranteed minimum nutrient content, says Coleman.

Hay pellets are typically 3/16 to ¾ inch in diameter. They, too, are easily weighed and stored and can be fed as a 100% alternative to long-stem hay with a guaranteed minimum nutrient content. Because hay made into pellets has been ground to smaller particle sizes than hay intended for cubes, horses might consume them faster.

Whether you choose to feed hay cubes or hay pellets, Coleman recommends soaking them in water to soften them for senior horses as well as reduce possible incidence of choke from eating them in their dried state.

Chopped hay is usually chopped to a length of about 1 inch, and you can purchase it bagged. Because of its shorter stem length, this form of hay is easier to chew and might be a good choice for senior horses with poor detention or in a total mixed ration for horses consuming a complete feed.

Dehydrated hay is a chopped hay product that is dehydrated and compressed into a block. The advantage dehydrated hay offers over regular sun-cured hay is it retains its maximum nutrient value with storage. As with the cubes and pellets, this product comes with a guaranteed minimum nutrient content.

Another excellent forage option for horses is haylage, because it provides a high-quality product that is dust-free. Haylage has a moisture content of 20-30% compared to dry hay’s approximately 14% moisture content. In Europe, feeding haylage is common practice, says Coleman. “It looks like regular long-stem hay and has a sweet smell to it,” he says.

Because of the fermentation process involved in making haylage (which increases the level of soluble carbohydrates), this type of forage might not be appropriate for horses with metabolic issues or prone to laminitis. It’s also at risk of botulism contamination if the packaging is not airtight, so ensure horses eating haylage receive a botulism vaccine.

Concentrate Decisions

The final part of creating a diet for your horse is the concentrate. Concentrate, for all intents and purposes, is the nonforage portion of the ration (grains, protein supplements, oils/fats, molasses). Not all horses need a concentrate in their diets. If the horse is at maintenance, for instance, he likely needs only a vitamin/ mineral supplement (ration balancer), says Parker. A concentrate might be an appropriate addition to the diets of horses that cannot get enough nutritional sup- port to maintain optimum condition from hay alone or cannot consume enough hay to maintain optimum condition (growing horses, mares in late gestation or early lactation, horses in intense work, and aged horses).

Parker stresses that the amount of concentrate you feed should be no more than that necessary to provide the horses’ required energy and other nutrients. If your horse needs a concentrate to stay at a healthy weight and body condition, then each feeding amount should provide no more than 0.5% of his body weight.

Final Thoughts

Creating the right diet for your horse involves considering many factors, including the science behind what we feed and how current research and knowledge can help us tailor the horse’s diet to meet his specific needs. Work with your veterinarian or an equine nutritionist to ensure your horse is getting the right nutrients in the appropriate amounts for his lifestyle.

This common pasture grass is good for grazing but bad for broodmares

If you look out over your pasture and see bunch grass with course-textured, flat, and ribbed-surface leaf blades, you are probably looking at tall fescue. Tall fescue, a productive, well-adapted, and persistent cool-season grass is one of the most abundant and heavily utilized forages in the United States. This grass occupies more than 10% of the U.S. land area—­approximately 37 million acres—with an estimated 700,000 horses grazing or fed tall fescue.

From a historical perspective, says Kyle McLeod, PhD, associate ruminant nutrition professor at the University of Kentucky, in Lexington, tall fescue (Festuca arundinacea Schreb.) was thought to have been introduced into the United States as a contaminant in the meadow fescue seeds imported from England until the late 1880s. It was recognized for its ability to thrive and was cited for its superior growth; tolerance of extreme conditions, disease, and insects; and ability to withstand heavy hoof traffic and grazing. By the 1940s two cultivars were released: Alta and Kentucky-31 (KY-31). Alta was selected for its winter hardiness, persistence, and ability to remain green even during drought conditions. This cultivar was planted throughout the Pacific Northwest and intermountain regions of the western U.S. The Kentucky-31 cultivar was noted for its adaptability to a wide range of soil types and ability to provide grazing throughout much of the year. The southern U.S. experienced a wide planting of KY-31 for forage, soil conservation, and roadside coverage. To date, tall fescue ranges from Florida to Canada.

Because of its nutrient composition and agronomic traits, tall fescue is the forage base of most livestock enterprises, particularly beef cattle. Jim Henning, PhD, former extension forage professor at the University of Kentucky, says well-managed fescue produces a high-quality forage with crude protein (CP) and digestible energy (DE) concentrations from vegetative (the period of growth between germination and flowering) to boot (the reproductive stage when the seedhead is enclosed within the sheath of the flag leaf) to mature stages of growth, ranging from 11% to 16% CP and approximately 60 to 68% DE (mature to vegetative).

Tall Fescue’s Side Effects

Despite all its positive traits, tall fescue is not without shortcomings. By the 1950s, says McLeod, fescue had gained a reputation for causing poor performance in livestock—primarily cattle but also small ruminants and horses—­consuming the grass. Cattle often developed a chronic, unthrifty condition, especially during the summer. Some occasionally developed lameness and lost portions of their feet and tails during fall and winter. Other perceived side effects included failure to shed winter coats, and, thus, heat intolerance, and reduced conception rates. Mares on tall fescue appeared to have higher foal mortality and agalactia (absence of milk production).

Scientists began studying the cause of these signs, says McLeod, and by the mid-1970s USDA researchers discovered an endophytic fungus that infects the fescue plant. “Endo” (within) plus “phyte” (plant) means a plant that lives within another plant. In this case the host is the fescue plant, and the toxic endophyte is a fungus identified as Epichloe coenophialum. Two characteristics of the endophyte have great practical importance. First, the organism does not affect either the growth or the appearance of the grass, and it requires a laboratory analysis to detect its presence. Second, it is transmitted solely by seed. So, the endophyte is beneficial to the plant but toxic to grazing livestock.

Krista Lea, MS, horse pasture evaluation program coordinator in the Department of Plant and Soil Sciences at the University of Kentucky, says the toxic endophyte produces several ergot (fungus) alkaloids (nitrogen-containing metabolites of the plant), including ergovaline, ergotamine, ergocristine, and lysergic acid, with ergovaline being the most prevalent (84-97% of the total ergot alkaloids produced). Although all classes of horses can experience endophyte-related issues, pregnant mares develop the most pronounced problems.

Lea says pregnant mares grazing endophyte-infected fescue might carry their foals several weeks past their due date, resulting in dystocia (difficult birth) because of the increased size of the foal. Thickened and/or retained placentas are common for mares grazing endophyte-­infected fescue. Frequently, the foal arrives normally but is encased in a tough and thickened chorioallantois (membrane surrounding the foal in the placenta), which he cannot break through. Consequently, he might suffocate unless someone cuts open the chorioallantois immediately. Premature placental separations (commonly referred to as red bag deliveries) are also common in mares grazing toxic endophyte-infected fescue.

Further, says Bob Coleman, PhD, PAS, associate equine extension professor at the University of Kentucky, mares grazing endophyte-infected fescue produce reduced amounts of or no milk and colostrum (antibody-rich first milk). Colostrum might contain lower concentrations of the antibody immunoglobulin G (IgG) and, in some cases, IgG absorption is lower in foals born to mares grazing toxic endophyte-infected fescue.

Scientists don’t know the exact mechanisms that cause these reproductive problems in mares; however, they do know the ergot alkaloids are agonistic to ­dopamine (D2) receptors, meaning they cause excess dopamine production. Research conducted in 2000 by now-retired Marc Freeman, PhD, and colleagues in the Department of Biological Sciences at Florida State University, in Tallahassee, revealed a significant reduction in circulating and releasable prolactin (a hormone essential to the final stages of birth) from the anterior pituitary gland and agalactia in mares grazing endophyte-infected fescue. Another contributing factor to prolonged gestation is suppression of the hormone progesterone. Progesterone levels should increase about two weeks before parturition (foaling), but mares consuming endophyte-infected fescue have reduced progesterone levels.

Grazing endophyte-infected tall fescue does not appear to have as much impact on other classes of horses, says Coleman. In one study conducted at Auburn University, researchers looked at the growth and development of yearlings grazing endophyte-infected fescue pasture. In another study a team at the University of Georgia considered the growth and development of yearlings eating endophyte-infected tall fescue hay. Neither research group found significant differences on average daily gains or wither heights of horses consuming fescue compared to controls.

A team from Missouri State University evaluated performance horses fed endophyte-infected fescue seed mixed in their grain ration and found no significant impact of the infected fescue on the parameters measured. Lea says researchers at the University of Kentucky have tested ergot alkaloids’ vasoactivity (ability to cause blood vessels to contract or dilate). While they documented vasoconstriction, with ergovaline being the most vasoactive ergot alkaloid, the horses did not appear to be outwardly affected.

Measuring Endophyte Levels

So, what can breeders do from a management perspective to avoid tall fescue toxicity in broodmares? Lea and Coleman agree that pasture management is the ideal option.

The first step is to know for certain the pasture is infected and at what level. For specific sampling procedures, costs, and shipping requirements, contact your local county Cooperative Extension office. However, here are some general sample collection guidelines:

When to sample. Samples must be collected when the plant has been actively growing for at least a month; this provides the best opportunity to find any endophyte present.

Collection. Gather tiller (stem) samples of the plant that are at least 1/8-inch thick. Cut with a razor or sharp knife at the soil surface, avoiding stems that have seedheads. Take at least 10 to 20 random tillers per five acres to get a representative sample of the pasture.

Storage. Place samples with a cold pack in a sturdy, plastic-lined box to take to a county extension office or overnight express to a testing laboratory. Refrigerate samples to ensure sample quality.

Results. The report you receive will indicate the percentage of submitted tillers that were infected with the endophyte. Some U.S. laboratories also determine ergovaline concentrations.

Lea says ergovaline concentrations vary seasonally and closely follow the tall fescue’s cool-season growth curve, with spikes occurring in spring and fall. However, some farms do not test for ergovaline concentrations. Based on data collected over the past 15 years through the University of Kentucky’s Horse Pasture Evaluation program, Lea’s team has developed a relative (ergovaline was not tested or tested outside of the normal months) risk scale to help breeders manage late-term mares’ grazing. Here is an excerpt from the table:

Because the ergovaline produced by the endophyte is what causes problems in broodmares, knowing how much ergovaline the mare is ingesting will provide you with more detailed information to guide your management practices. Researchers have shown that signs of fescue toxicity appear in pregnant mares consuming fescue testing greater than 300 parts per billion (ppb) of ergovaline. However, most extension publications suggest using 200 ppb as the threshold value. The University of Kentucky team has established risk levels for late-term pregnant mares based on ergovaline concentrations in the total diet (see table below).

Most pastures are not 100% tall fescue, says Lea. Pastures contain other grasses and legumes mares prefer to eat, thus diluting the actual amount of ergovaline in the pasture. You can calculate the amount of ergovaline in the pasture based on the estimated percentage of other grasses or legumes in the field, using this formula:

% tall fescue
_________________
(% tall fescue + % grass A + % grass B) x ergovaline (ppb)
=
ergovaline in available forage

From this calculation you can determine your mare’s risk level for grazing a pasture.

Management Strategies

Remove pregnant mares from any pasture (or hay) containing endophyte-infected tall fescue 60 to 90 days pre-foaling, says Coleman. You might move mares to a drylot area where you can meet their nutrient requirements with hay and concentrate or to a pasture with forage species other than endophyte-infected tall fescue. Agronomists and researchers consider this the most conservative way to avoid toxicity problems.

For mares in the moderate to high-risk category, you can administer domperidone, a drug that stimulates normal prolactin and progesterone production, to avoid agalactia and dystocia. Domperidone should be administered daily for 30 days prior to foaling. Grazing and/or mowing the pasture will keep the fescue plants young and in the vegetative state. Coleman stresses the importance of not overgrazing the pasture, because the endophyte is in the basal part of the plant in addition to the seedheads. Don’t let the horses graze the grass below 3 inches, says Lea.

You can also dilute endophyte-infected tall fescue in a pasture by incorporating other grasses and legumes. Because tall fescue is not the most palatable grass, mares will choose not to eat it if something more desirable is available. With this strategy you will also benefit from improved pasture quality and production.

Although an expensive option, the final management strategy might be to kill infected stands and replant. Lea says there are essentially three types of tall fescue:

1. The toxic endophyte, naturally occurring Kentucky-31. This is a very hardy and persistent grass and is the one causing the toxicity problems—it’s the type you are trying to get rid of in your pastures.
2. Endophyte-free tall fescue (e.g., Teton II, Select, Tower, Bronson). This grass does not contain an endophyte, so it is safe for horses to graze. Its downside is it’s not very hardy and cannot tolerate heavy grazing. If you plant this tall fescue, be ready to reseed repeatedly.
3. Novel endophyte tall fescue (e.g., Jesup MaxQ, Tower Protek, Kora Protek, BarOptima PLUS E34, Estancia ArkShield, Martin 2 Protek, Lacefield MaxQII). The endophyte contained within this plant still provides it with hardiness but does not produce the toxic compounds; therefore, horses can graze this fescue safely. Consult your local herbicide dealer to determine the best option for renovating your pasture.

Take-Home Message

Because tall fescue is a popular and well-established grass across pastures in the U.S., eliminating the risk of toxicosis in broodmares is nearly impossible. The only way to avoid fescue toxicosis is to understand the nature of the plants in your pasture. Know when ergovaline levels will be high, and choose the most beneficial management options to reduce the risk to broodmares

Q: My mare is due in April. Right now my veterinarian says she’s at a healthy weight, but I’m worried she might lose weight as she gets closer to foaling and once she starts nursing. How will her nutritional needs change immediately before and after she has her foal, and how can I be sure her diet meets her energy needs?

A: Great question, and you’re right to wonder about the nutritional needs of your broodmare because they change as she progresses in her pregnancy and through lactation.

While your vet indicated your mare is currently at a good weight, it is also important to know your mare’s body condition score (BCS). Ideally during late gestation, you want her to have a BCS between 5 and 6 using the Henneke body condition scale of 1-9 (with 1 being extremely thin and 9 being extremely fat). It can be beneficial for a broodmare to carry a little extra body condition during this time, so she has a buffer of body fat stores during the high energy demands of lactation. Being able to recognize and assess your mare’s BCS will help you ensure her diet is adequate in calories. However, just because a mare is in good body condition does not guarantee proper fetal development. Other nutrients such as protein, minerals, and vitamins are also needed to ensure a healthy future for your foal.

Mare Nutrient Requirements in the Second and Third Trimester

Some of your mare’s nutrient requirements begin to slightly increase during her second trimester, beginning around the fifth month of pregnancy. But it’s really in her last trimester, starting around month 8, that her unborn foal begins to develop more rapidly, gaining both weight and body size. In fact, the fetus will gain approximately 1 pound per day in the last three months of gestation and will be approximately 60% of its mature height at birth.

Your mare’s diet should meet her daily nutritional needs because if it does not, her body will deplete itself to meet the demands of the growing fetus. Her increased requirements for energy, protein, and trace minerals—most notably calcium, phosphorous, and copper—are vital for proper fetal development and ensure adequate milk production after the foal is born. Additionally, late gestation mares do not increase voluntary intake to match their higher nutrient demands, so simply feeding more is not necessarily a viable option to give her additional nutrition.

Feeding the Late Gestation Broodmare

Forage should always be the main component of the diet, but even high-quality forages lack the protein, vitamin, and mineral fortification the mare needs during late gestation. For example, high-protein forages such as alfalfa are not well digested in the small intestine and could result in inadequate intake of amino acids. Supplementing with a high-quality concentrate feed designed with broodmares in mind and fed at the appropriate amount will ensure you are meeting her nutrient needs. If your mare is an easy keeper, a ration balancer would be appropriate if she is getting enough calories from her forage to maintain body condition.

Feeding Lactating Mares

Once your mare begins lactating, her nutritional needs for energy, protein, minerals, and some vitamins will increase significantly. For example, her energy needs are double that of her maintenance requirements.

While mares in late gestation might not increase their feed intake, lactating mares tend to have much greater appetites and your feeding program should reflect this. Lactating mares can consume up to 3% of their body weight in dry matter intake and at least half of this should be in forage. Once again, good-quality hay or pasture is recommended due to high nutrient demands. Feeding rates will vary depending on the quality of your hay or pasture and whether your mare is a heavy milker or a hard- or easy keeper.

Most lactating mares cannot meet their high energy and nutrient demands consuming forage only. I recommend feeding a concentrate designed for broodmares to support milk production, provide essential nutrients for the foal, and help maintain your mare’s body condition. Feed according to manufacturer’s instructions for her weight and stage of lactation. Always increase feed gradually to the full feeding amount over a seven-to-10-day period to prevent digestive disturbance.

Take-Home Message

The best start for a foal begins with proper nutritional management of the mare. Broodmare owners benefit from learning body condition scoring and recognizing their mares’ specific nutritional needs before and after foaling.

Do you have an equine nutrition question?

Tailor your dam and foal’s feeding program from late pregnancy to weaning with expert guidance.

As your mare approaches the final stages of pregnancy, the countdown to her foal’s arrival can feel like an eternity. But while it might seem like little is happening, the final three months of gestation are critical for both the mare and the unborn foal. Planning the mare and foal diet becomes important.

During this time her nutritional needs intensify, and a carefully planned feeding program becomes essential to ensure both mare and foal thrive.

Here, Kris Hiney, PhD, an extension specialist and associate professor at Oklahoma State University, in Stillwater, and Laurie Lawrence, PhD, a professor in the University of Kentucky’s College of Agriculture, Food and Environment, in Lexington, share their insights on creating an effective feeding strategy to support your mare’s late-stage pregnancy and the foal’s early development.

Feeding Late-Gestation Mares—The Last 90 Days

Hiney explains that until the last 90 days of your mare’s pregnancy, the feeding routine mimics that of a horse in light work. However, during the final three months, her nutritional needs increase to support both her energy requirements and the developing fetus.

“The nice thing is that late-gestation mares are not hard to feed as long as you’re making sure (they are) in good body condition,” Hiney says.

Veterinarians and equine nutritionists consider a score of 5 to 6 on the Henneke body condition scale ideal for these mares. At that level you might not see the ribs but can easily feel them. A horse at a 6 has a little more fat cover, but you shouldn’t have to dig to find a rib on the horse. In colder climates Lawrence prefers mares stay at a 6 in the last three months of gestation to ensure they have enough reserves for lactation.

“Mares that are heavy milkers may benefit from being close to 6 so they don’t become skinny during lactation,” Lawrence says. “Every mare is an individual, but I would recommend that she have free access to good-quality hay, possibly an alfalfa-grass mix (grasses such as timothy or orchard grass), or good-quality pasture, or a combination of both and then enough concentrate to maintain a body condition score between 5 and 6.”

Pasture as Part of the Mare’s Diet

Indeed, grass can be an acceptable forage source so long as it’s good quality. Pasture is not merely something with a fence around it, says Hiney. If you rely on pasture to meet your mare’s nutrient requirements, it must contain grass species—not weeds or forbs (flowering plants with broad leaves and soft stems). For maximum nutrition, grass should be 4 to 6 inches high because grass in the early stages of growth contains higher nutrient levels.

“If the forage is sparse, I might be worried that it’s not going to meet that broodmare’s nutrient needs,” Hiney says. “That doesn’t mean pull her off pasture, but you might need to step in with supplementation.”

Both Lawrence and Hiney stress that when grazing mares on tall fescue or feeding fescue hay, it must be free from the toxic endophyte found in some of these plants. Endophyte-infected fescue can cause health complications in late-term mares such as prolonged gestation, dystocia (difficult birth), and low or no milk production, and it increases the fatality risk in foals.

Formulated feeds also make up part of the ration equation for most horses. Late-gestation mares weighing around 1,200 pounds need 2 to 3 pounds more grain than their nonpregnant counterparts, Hiney explains. But this depends on several factors, including forage quality and the energy density of the feed concentrate.

“If access to pasture is unavailable and/or hay is limited, mares could require a high-quality grass hay at 1% of her body weight in combination with as much as 6 to 7 pounds of a typically formulated grain mix daily,” Hiney says.

Feeding Lactating Mares and Foals to 3 Months Old

The minute the foal touches the ground, your mare’s nutritional needs skyrocket. The foal relies on mom exclusively for his nutritional needs until about 2 months of age.

“People don’t realize how much milk production ups her nutrition needs,” Hiney explains. They “go up to almost twice as much as a maintenance horse. That’s a big jump if you haven’t had broodmares.”

On average, a 1,200-pound mare needs 12 to 15 pounds of an average-energy-density grain mix in addition to 10-12 pounds of a good-quality hay to meet her energy needs at this point, says Hiney. Protein plays a critical role during this time frame, and Hiney says owners commonly supplement mares with a 16% protein concentrate. However, consider the forage source—get the hay tested—before determining how much concentrate to provide.

“If you’re feeding 18% (protein) alfalfa hay, the mare is already getting quite a bit of protein from that source,” Hiney says. “You have to know what’s in the forage and then map it out.”

Lawrence adds that mares can produce 5 gallons of milk or more per day during lactation, most of which consists of water. Therefore, she recommends providing an abundant water supply. It should be the equivalent of at least two 5-gallon buckets of water per day.

The Foal Diet

While milk is the primary nutrient source for foals under 2 months of age, most will start eating their mother’s feed and hay soon after birth. By about 2.5 months of age, the foal’s nutrient needs exceed the nutrients provided by milk alone, so you need to provide enough good-quality forage for him, as well.

“At this time, it is probably a good idea to start introducing the foal to its own feed tub and providing some concentrate (one-half pound or so to start) twice a day,” Lawrence says. “Some babies are really aggressive and run their mothers from the feed tub.”

Hanging feed tubs out of the foal’s reach can keep him out of mom’s ration. Nose bags for the mare are another option. Similarly, mares might need to be kept out of the foal’s portion. Feeders with bars set narrower than the mare’s muzzle and paddock exclusion areas that only the foal can enter can prevent the mare’s consumption. Putting the mare and foal in separate stalls during feeding serves a dual purpose of preparing the two for weaning.

Mares and foals can quickly look unthrifty if the mare does not receive adequate nutrition. Lawrence and Hiney agree it’s essential to observe the mare and foal closely and assess their body condition scores regularly to make necessary feeding adjustments as soon as possible. Fortunately, mares typically eat more forage and supplemental concentrates when provided.

“Keep in mind that when pasture is abundant, some mares will gain weight and may not need a true concentrate feed, but they still need mineral fortification,” Lawrence says. “Offering 1 to 2 pounds of a ration-balancer feed can be the solution to meeting needs without adding extra calories that result in excess weight gain.”

Feeding Foals 3 Months Old to Weaning

By 3 months of age, a foal consumes and uses nutrients from pasture, hay, and concentrate feeds in addition to continuing to nurse. Gradually increasing his ration during the next few months helps reduce the amount of stress experienced at weaning.

“At six months, you want the foal eating what he will be eating when weaned,” Hiney says. “Nutritionally, that is the least stressful for him (compared to) an abrupt change in grain or forage.”

Lawrence shared the advice of one of her mentors: Feed one-half to 1.5 pounds of concentrate per month of age. That would mean the foal receives 2.5 to 7.5 pounds of concentrate by the time he’s weaned at 5 months old. Generally, the foal approaching weaning should consume 3 to 5 pounds of concentrate (formulated for growing horses) with good- to high-quality forage.

“That seems like a huge range, but it would be adjusted on the size of the foal and the quality of the forage,” she says. “If the forage is low in digestibility and nutrients, then more concentrate is needed. Likewise, if the forage is ultra-high quality, then the lower range is used.”

Keep in mind overfeeding can lead to rapid growth, which increases the risk of joint and bone diseases such as osteochondritis dissecans (OCD), a condition commonly diagnosed in young horses. This issue occurs when joint cartilage doesn’t form properly, leading to inflammation and potential lameness. Excessive growth can also simply stress the developing musculoskeletal system.

On the other hand, a young horse that isn’t receiving enough nutrition and is growing too slowly might experience stunted development.

Feeding the Mare At Weaning

As the foal’s ration increases, the mare’s should decrease, says Hiney. For example, if the dam receives 10 pounds daily, backing down to 7 or 8 pounds helps prepare her for the transition as well.

After weaning, don’t forget the mare. First, nursing is the main stimulator of milk production. Once the foal is gone, the mare’s supply will dry up, Lawrence explains. Removing her feed does not make this happen.

“Second, we are pretty sure that mares mobilize some mineral stores during late gestation and lactation to maintain milk production and all of her own important body functions,” she says. “This happens in women who are nursing to some extent, regardless of nutrient intake.”

In women, depleted mineral stores (in the bones) are replaced after lactation ends. This likely happens in mares as well. But in many mares the end of lactation coincides with the fourth or fifth month of gestation if they are rebred.

“Important fetal development is occurring at this time, and the accumulation of fetal mass begins to escalate,” Lawrence says. “The window of opportunity to replenish stores is probably small. Fall pasture is often abundant, and mares maintain weight with minimal concentrate … but fortification is still needed, so (this is) another opportunity to use a balancer pellet. If a mare ends lactation with a body condition score of 5 or less, then concentrate intake is maintained to provide for both replenishing of fat stores and other stores.”

Mare and Foal Diet – A Balancing Act

Mares and foals through late gestation to weaning need sufficient nutrition to support overall good health. Providing the dam enough forage and concentrate feed to maintain a body condition score of 5 to 6 requires a balance of skill and knowledge. But avoiding overfeeding—especially in young horses—holds equal importance to avoid joint disease. A well-designed and managed feeding program promotes steady, moderate growth, helping the young horse reach his potential while taking into account his unique needs

Many newborn foals need specialized care to address medical challenges that commonly arise during the first weeks of life. During their presentation at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida, two board-certified internal medicine specialists—Laura Javsicas, VMD, Dipl. ACVIM, of Rhinebeck Equine, in New York, and Lisa Edwards, DVM, Dipl. ACVIM, ACVECC, of the University of Florida’s College of Veterinary Medicine, in Gainesville—shared their protocols for treating equine neonatal health issues in the field.

Diarrhea in Newborn Foals

Loose manure in foals can cause important health problems, with severity often varying by age. Neonates under 24 hours old with hemorrhagic diarrhea need immediate attention because this bloody manure can indicate clostridial (a type of bacteria) infection in the abdomen and an increased risk of sepsis (bacteria in the bloodstream). Diarrhea in foals over 2 weeks of age typically concerns practitioners less but still warrants veterinary care.

When managing foals with diarrhea, Javsicas and Edwards generally treat them with a di-tri-octahedral (DTO) smectite for toxin adsorption and intravenous (IV) fluids with dextrose for hydration and nutrition, and they conduct bloodwork to assess electrolyte imbalances, glucose and lactate levels, and renal function. Additionally, performing polymerase chain reaction (PCR) testing on the foal’s manure could help veterinarians identify the infectious agents.

Javsicas and Edwards said veterinarians prefer the antibiotic ceftiofur to treat diarrhea in foals and add metronidazole if they suspect a clostridial infection. The veterinarians added that ultrasound and nasogastric tube (NGT) placement are critical for identifying and relieving any gastric reflux in foals with diarrhea and coliclike signs.

Dehydration and Electrolyte Imbalances in Newborn Foals

Foal diarrhea poses a significant risk of dehydration and can lead to life-threatening electrolyte imbalances, especially hyponatremia (low sodium). For severe dehydration cases veterinarians can turn to a continuous rate infusion (CRI) of IV fluids. Balanced electrolyte solutions are ideal; veterinarians can also add dextrose and sodium bicarbonate (to counteract severe metabolic acidosis) if necessary, Javiscas said.

Both veterinarians recommended closely monitoring foals’ urine output during rehydration as a key indicator of kidney function. They also warned that despite practitioners’ best efforts to manage these cases on the farm, foals with severe electrolyte imbalances or signs of septicemia warrant a hospital referral.

Patent Urachus in Newborn Foals

A patent urachus occurs when the connection between the bladder and umbilical cord fails to close after birth. Veterinarians typically see this condition in foals that spend more time lying down than normal (i.e., “bed babies”), twins, or foals with abnormal or infected umbilical cords. They can treat most cases medically with antibiotics and local wound care, but regular ultrasound monitoring is important to assess the urachus and ensure there are no deeper infections, said Javiscas and Edwards.

Common patent urachus treatments include hypochlorous acid products and povidone-iodine (Betadine), which also have a skin-drying effect that can be beneficial in these cases, Javsicas said. Veterinarians generally only consider surgery if the condition doesn’t improve with medical treatment after 10 to 24 days.

Milk Replacement

Sick foals that cannot nurse need equine-specific milk replacers; Javsicas and Edwards noted that using milk formulated for other species can lead to diarrhea and electrolyte imbalances. If a neonate cannot nurse from its dam, veterinarians might use bottle or NGT feeding as alternatives. But if a foal can’t ingest milk from any source for any significant amount of time, veterinarians should provide IV dextrose supplementation and complete parenteral nutrition.

Take-Home Message

With strategic and resourceful field care, veterinarians can significantly improve outcomes for newborn foals affected by common health issues. Edwards and Javsicas emphasized the importance of thorough diagnostics, timely interventions, and informed treatments to protect neonatal health during this critical stage.

Q. My mare had her first foal last week—a beautiful filly! Everything started out very well. The filly nursed, and my mare accepted her without issue. However, now the foal isn’t gaining weight. I’ve heard that sometimes maiden mares don’t create enough milk. Should I supplement her with milk replacer?

A. Congratulations on the birth of your filly! Having a foal can be enchanting, although at the same time quite stressful because so many things can go wrong. If you haven’t done so already, I strongly recommend contacting your equine veterinarian, who might want to assess the foal and rule out any medical cause for the lack of growth.

Sometimes a mare doesn’t produce enough milk to support the foal’s demands. Foals of this age are nursing in the rage of four to six times per hour, and this suckling action helps stimulate milk production. The demands made on the mammary tissue early on help set the stage for how much milk the mare will produce later. Plenty of early suckling is important so the mare can support the foal’s needs as she grows. If the issue is that the foal does not have much drive to nurse, a veterinarian will need to determine the cause.

If given your vet’s “all clear” to supplement with milk replacer, you’ll find several good commercially produced ones designed specifically for foals. Use these and not replacers created for other species such as goats or cattle. Every species has a milk composition slightly different and unique to their needs.

Because of the need for frequent suckling, feed the foal ad lib milk replacer is best, making sure it’s constantly available. This is better than meal feeding her at times that are convenient for you but perhaps not in sync with when the foal wants to nurse. Also, presenting a foal with infrequent large replacer amounts at once risks overdrinking, and milk might end up in the hindgut where it can disrupt microbial population development.

Keep track of how much replacer the foal is consuming each day. A foal born to a 1,000-pound mare might consume up to 4 pounds of replacer a day, at which point you can transition to free feeding a milk-based pellet.

Make sure you’re creating the milk replacer with a dry matter content of 10%. Less than this level of dry matter might leave the foal hungry. From month one to four the foal might consume 1 pound of replacer per 100 pounds of her body weight. The amount of milk the mare is providing will dictate how much the foal needs to consume from the supplemental source, so don’t be alarmed if you see some variation in how much she consumes each day. Keep a journal so you can see the daily consumption level and be able to identify when you can transition to pellets or to record signs indicating she needs veterinary support.

With careful management and supplementation, you should be able to ensure your foal is receiving the correct plane of nutrition to fully meet her genetic potential and develop at an appropriate rate.

Aging mares play a key role in advancing equine breeding programs, but pituitary pars intermedia dysfunction (PPID), formerly known as equine Cushing’s disease, might interfere with their reproductive performance. Testing broodmares 15 years old and older for this disease and treating when needed might help minimize the negative consequences of PPID on mare fertility, said Sophia Panelli Marchio, DVM, a PhD candidate at Texas A&M University’s College of Veterinary Medicine, in College Station. Marchio spoke about the effects of PPID on mare fertility during her presentation at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida

What is PPID in Horses?

Pituitary pars intermedia dysfunction is a neurodegenerative disease that progresses with age, with worsening clinical signs in older horses. Following stimuli such as stressful events, thyrotropin-releasing hormone, or TRH, stimulates melanotropes—cells that produce melanocyte-stimulating hormone—in the pars intermedia of the pituitary gland to express a gene called pro-opiomelanocortin (POMC). The body then breaks POMC into smaller hormones, including adrenocorticotropin hormone (ACTH). In turn, the horse’s body releases ACTH into circulation where it stimulates the adrenal gland to release a variety of compounds and hormones. 

Dopamine produced by dopaminergic neurons in the hypothalamus inhibits the production of ACTH and other POMC-derived hormones. Thus, horses with neurodegeneration of the dopaminergic neurons lose control over the production of ACTH and other hormones. Often, they overproduce these hormones and, as a result, hyperplastic growth—an abnormal increase in cell number—of the pars intermedia.

Recognizing and Diagnosing PPID in Horses

Classic signs of PPID include polydipsia and polyuria (excessive drinking and urinating), hyperhidrosis (extreme sweating), secondary infections, lethargy, neurologic problems, abnormal fat distribution, hirsutism (a long, shaggy coat due to abnormal shedding), hyperinsulinemia-associated laminitis (HAL), muscle wasting, and a pendulous abdomen.

Veterinarians most commonly diagnose PPID by measuring basal (resting) ACTH levels.

“If evaluating basal ACTH, veterinarians must appreciate that the reference values will change based on season,” said Marchio. “ACTH values can also differ if the animal has been through a stressful situation.”

Effects of PPID on Mare Fertility

In addition to the clinical signs mentioned above, broodmares with PPID might experience an absence of seasonal anestrus, abnormal cycles, anovulatory follicles, subfertility, recurrent endometritis, and abnormal lactation.

“Dopamine plays an important role in controlling reproductive hormones,” said Marchio. “It regulates reproductive seasonality and inhibits cyclicity during the anovulatory season.”

The POMC-derived hormones, including ACTH, increase in mares with PPID. To determine the effect of high ACTH on reproduction, researchers on one study (Hedberg et al., 2007) treated healthy mares with ACTH. “They found a higher concentration of steroid hormones that inhibit gonadotropin-releasing hormone (GnRH) release and an increase in cortisol,” said Marchio. “In turn, high cortisol can repress GnRH as well as luteinizing hormone (LH) release. Further, high follicular fluid cortisol levels can disrupt oocyte quality.” Researchers on another study of healthy mares treated with the synthetic glucocorticoid dexamethasone also reported a reduced LH concentration (Asa et al. 1982).

“Only one study clearly correlates ACTH with impaired reproductive performance (Tsuchiya et al., 2021),” said Marchio. “As ACTH increased, cortisol increased, and mares had lower reproductive success determined by live foaling rates.”

Marchio also said researchers believe the enlargement of the pars intermedia can compress the pars distalis and interfere with the production and release of follicle-stimulating hormone (FSH) and LH, impairing the mare’s cyclicity. They also hypothesize that recurrent endometritis might develop due to the immunosuppressing effects of high cortisol levels.

Treating Broodmares That Have PPID

Administering a dopamine agonist such as pergolide (an FDA-approved dopamine receptor agonist labeled for treating clinical signs of PPID) or cabergoline (another dopamine receptor agonist) and good management practices improve the well-being and reproductive performance of aged broodmares with PPID, said Marchio.

“Be certain to suspend pergolide treatment at least 30 days before foaling and implement the treatment 30 days after foaling as it can interfere with lactation,” she added.

Take-Home Message

Formerly known as equine Cushing’s disease, PPID in horses might have negative effects on mare fertility. “We only have hypotheses on how PPID affects reductive performance,” said Marchio. “The exact mechanisms are still unknown and must be studied in depth utilizing horses with PPID.”

Equine herpesvirus-1 (EHV-1), a significant cause of respiratory and neurological disease in horses, can spread stealthily at equestrian events, often going unnoticed. Nicola Pusterla, DVM, PhD, Dipl. ACVIM, AVDC-Equine, professor of equine internal medicine and epidemiology at the University of California, Davis, School of Veterinary Medicine, recently led research on the role that subclinical shedders—those that do not show signs of infection—play in spreading the virus. He presented his findings at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida, and raised concerns about current practices for detecting and managing EHV-1.

Silent Shedding and EHV-1 Environmental Spread

Horses that appear clinically healthy might still shed EHV-1 and contribute to outbreaks, complicating efforts to prevent viral spread. Pusterla’s research team tested 162 apparently healthy horses at a California horse show in April 2022. While only three (1.85%) horses tested positive for EHV-1 using quantitative PCR (qPCR), testing environmental samples from stalls revealed more positive results.

Immediately after the event the researchers collected sponges (specifically used to collect samples) from stalls and identified, among others, five EHV-1-positive stalls in one barn. “This clustering pattern confirms that the respiratory virus can easily spread among horses sharing close quarters and suggests that transmission might occur more subtly than we previously understood,” Pusterla said.

Focusing on EHV-1 Environmental Detection

The research team conducted a second study to evaluate the accuracy of environmental sampling in detecting EHV-1. They collected samples daily for 11 days using nasal swabs, stall sponges, air samples, and stall strips in an eight-stall barn housing seven adult horses aged 5 to 16 years old. Four horses had been vaccinated with a modified-live intranasal EHV-1 vaccine to mimic subclinical shedding; the remaining three horses were unvaccinated.

All intranasally vaccinated horses shed EHV-1 in nasal secretions at levels and for a duration similar to what is expected in subclinical shedders, while none of the controls had detectable EHV-1 in nasal secretions (the EHV-1 vaccine strain is harmless and cannot be transmitted to other horses, hence it does not contribute to the spread of EHV-1). The team used sponges to detect EHV-1 in the stalls of all vaccinated and one control horse. With stationary strips they detected EHV-1 in the stalls of three of four vaccinated horses but none of the controls. Air samples showed low detection rates, likely due to low concentrations of aerosolized EHV-1.

“The highest detection rates came from stall sponges, particularly in feeding areas where droplet contamination from nasal secretions is likely,” Pusterla said. The researchers established that the virus did not necessarily transfer directly between horses but did accumulate in shared and high-traffic spaces such as stall walls and water buckets.

Implications for Biosecurity at Equine Events

Pusterla’s research highlights the importance of implementing biosecurity measures to control EHV-1 at horse shows. He reported that traditional diagnostic methods, such as nasal swabs, are invasive and might miss shedding. Environmental sampling, particularly with stall sponges, could offer a more effective and practical approach to identifying viral clusters and taking preventive measures. However, the study’s limitations include a small sample size and no assessment of viral viability in the environment.

Take-Home Message

Pusterla emphasized the need for vigilant monitoring and proactive strategies to mitigate EHV-1 risks. Farm owners and managers should prioritize good biosecurity practices with their hygiene and cleaning efforts, especially in areas prone to droplet contamination, such as feeding zones and high-traffic areas. Equally important, environmental testing could be a vital tool for early detection and prevention of outbreaks, helping limit the silent spread of EHV-1.

What vitamins and minerals does your horse need? 

Vitamins and minerals, referred to as micronutrients, make up only a small portion of the equine diet by weight, but their importance to our horses’ health is enormous. Micronutrients are involved in many key body processes, including muscle function, bone health, hormone signaling, digestion, acid-base balance, and much more.

Each micronutrient plays a significant role in a horse’s health, and no individual micronutrient is more crucial than the next, says Wendy Pearson, PhD, assistant professor in equine nutrition and physiology at the University of Guelph, in Ontario, Canada, “except if there is a dietary deficiency, then that one will be the most important.”

Modern horse diets are commonly deficient in some vitamins and minerals. Let’s dive deeper to learn about these micronutrients and find out when supplementation might be necessary.

What Micronutrients Could Your Horse Be Missing?

Horses synthesize some micronutrients in their hindguts. In reality, the horse itself isn’t making these nutrients; the diverse bacterial colonies that reside within the large intestine are. This symbiotic relationship between the horse and the microbial population produces several nonessential micronutrients—nutrients the healthy horse typically does not need to obtain from diet—including B vitamins, vitamin K, biotin, folate, and cobalt. Horses not eating enough dietary forage or those under stress, however, might require supplementation.

Then there are the micronutrients our horses must receive from their diets, termed essential micronutrients. Many horses can receive adequate micronutrients from a diet of quality forage and fortified ration balancer or commercial feed. However, in some cases our horses have different micronutrient needs based on workload, management, and/or life stage than what we provide in a standard diet. Below we will outline some of the most commonly deficient vitamins and minerals in the modern equine diet.

Calcium and Phosphorus

Function

Calcium and phosphorus are the two most abundant minerals in the horse’s body, and they work closely together. They’re also two of the most important components in the formation and maintenance of healthy bones and teeth, making them vital elements of the diet, particularly for growing horses. The skeletal system provides not only structural support for the body but also a place to store calcium, which is involved in many other functions, including muscle contraction.

Horses must consume calcium and phosphorus in adequate quantities as well as in the correct ratio. We typically discuss calcium and phosphorus together as a ratio due to their close relationship within the body and because phosphorus intake tightly regulates calcium absorption. Consuming less calcium than phosphorus can impede this absorption, which is why equine nutritionists recommend a minimum ratio of 1:1 of calcium:phosphorus.

When to supplement

Calcium or phosphorus deficiencies are the most common mineral deficiencies in horses. Horses that are growing, pregnant, lactating, or working require higher levels of calcium and phosphorus than adult horses at maintenance. This is due tothe increased calcium and phosphorus requirements for bone development and maintenance.

Though the minimum calcium-to-phosphorus ratio is 1:1, the National Research Council (NRC) recommends a ratio of 2:1, which happens to be the ratio of calcium to phosphorus found in bone. Researchers have found that a ratio of up to 6:1 is safe in horses. You can determine this ratio by looking at the calcium and phosphorus on your feed tag and via a hay analysis. Most hay varieties contain more calcium than phosphorus, with legume hays such as alfalfa containing the highest levels.

Vitamin E

Function

Vitamin E is a potent antioxidant that works alongside selenium to protect the body from free radical damage that occurs naturally in all horses due to oxidative stress. The term “vitamin E” describes a family of compounds that can be divided into two groups: tocopherols and tocotrienols. In feed formulations we most often see vitamin E in the form of α-tocopherol-acetate.

When to supplement

The NRC (2007) set the vitamin E requirement for a healthy 1,100-pound horse not in work at 500 international units (IU) per day. This requirement increases with exercise to 800 IU for light work and 1,000 IU for heavy work. However, many researchers suggest these levels underestimate vitamin E requirements, particularly for working horses. Additionally, horses consuming high-fat diets could require higher vitamin E intake to offset the additional breakdown of fat by free radicals in the body. Plus, researchers have reported that horses with neurologic diseases respond well to high doses of vitamin E (Finno and Valberg, 2012).

In the average horse’s diet, the most potent source of vitamin E is fresh forage, meaning horses without consistent access to fresh, green grass could need additional vitamin E. While hay can also contain vitamin E, levels decrease significantly with processing and storage (Finno and Valberg, 2012). Further, your horse’s feed might not supply sufficient vitamin E. While feed companies typically manufacture products fortified with vitamin E, your horse might still need supplementation, as not all vitamin E is absorbed and utilized equally.

Vitamin E supplements for horses come in natural and synthetic forms of α-tocopherol. The bioavailability of natural vitamin E is significantly higher than that of the synthetic form (DL-α-tocopherol), meaning the body can absorb and use it more readily (Fagan et al., 2020). We often see synthetic vitamin E in supplements or feeds, as it is more shelf-stable than natural vitamin E. When selecting an appropriate vitamin E supplement, however, look for products containing natural vitamin E (D-α-tocopherol).

Your veterinarian can easily determine your horse’s vitamin E status from a blood sample. Testing is less expensive than maintaining your horse on a vitamin E supplement for long periods ­unnecessarily.

Sodium

Function

Sodium is a mineral that is vital for healthy central nervous system and muscle function. As an electrolyte, it is an important regulator of fluid balance in the body.

When to supplement

Forage contains very low levels of sodium, and commercial diets generally contain less than 0.5% salt, meaning most horses, even those on fortified feeds, could need more sodium in their diets. This is especially true for horses in work or those in hot, humid climates.

In healthy horses excess sodium gets excreted easily in urine, so it is a relatively safe addition to your horse’s diet. Salt licks are a simple solution; however, for horses that receive concentrates or balancers, adding table salt to the diet ensures more consistent intake.

Vitamin A

Function

Vitamin A is an important micronutrient involved in vision, with night blindness being a classic presentation of vitamin A deficiency. Remember how we were always told that carrots help us see in the dark? Well, this is because carrots contain high levels of β-carotene, a compound the body metabolizes to form vitamin A. β-carotene is the plant form of vitamin A and the predominant type our horses consume. Vitamin A is also involved in horses’ immune response, reproductive function, muscle growth, bone development, and healthy skin.

When to supplement

The NRC says you have to feed extremely low levels of vitamin A—less than 10% of the recommended minimum intake—for clinical signs of deficiencies such as night blindness to occur, making it a very rare condition in horses. Fresh green grass is the best source of vitamin A, with minimal amounts being found in hay. Horses on an exclusively hay diet, especially pregnant and lactating mares, could need additional vitamin A. Horses on fortified feeds or those grazing fresh, green grass are rarely deficient in vitamin A, because manufacturers typically fortify commercial feeds, balancers, and vitamin/mineral supplements with this micronutrient. For this reason it’s usually unnecessary to provide additional vitamin A to these horses, and doing so can lead to toxicity.

Vitamin D

Function

Vitamin D plays an important role alongside calcium and phosphorus in bone development and maintenance. Vitamin D is produced predominantly in the skin when exposed to UV rays from sunlight, but horses can also get it from the diet. Fresh forage contains high levels of vitamin D, and hay contains low levels.

When to supplement

Current research is limited on vitamin D and horses. However, for horses in northern latitudes and those that live predominantly inside, are blanketed for most of the year, and/or consume a straight hay diet, vitamin D supplementation could be necessary, particularly for foals and growing horses. For these horses, equine nutritionists recommend adding a fortified commercial feed, balancer, or supplement with guaranteed vitamin D levels.

Simple Solutions

Major shortages of vitamins and minerals could result in dramatic signs of deficiency, such as skeletal deformities or night blindness, as well as subclinical (inapparent) problems. Minor micronutrient deficiencies might not be evident at first but could lead to complications down the line, such as improper bone development leading to lameness and/or reduced performance ability.

While most horses consuming a diet of fresh pasture plus a commercial ration balancer or concentrate have most, if not all, of their micronutrient needs covered, those consuming a straight hay diet likely need additional nutrients in the form of a fortified feed, ration balancer, or supplement, says Pearson. Life stage, exercise level, and management practices might also increase a horse’s need for supplementation of micronutrients in the diet beyond forage.

For horses that do not require the extra calories from a commercial feed, those ration or hay balancers can be excellent additions to a forage diet.

Use caution, however, when supplementing your horse’s diet. Arbitrarily adding micronutrients can throw things off balance or create issues with toxicity. Your best tool for making informed decisions on what nutrients your horse needs is a hay analysis. Consult an equine nutritionist or a board-certified veterinary nutritionist to best ensure your horse’s diet fits his individual needs.

Take-Home Message

Micronutrients are tiny but critical components of our horses’ diets. While some vitamins and minerals can be made endogenously (within the horse), most come from the diet. The most important micronutrients in horses’ diets are the ones they are deficient in. Performing a hay analysis and consulting an equine nutritionist are the best methods to avoid micronutrient deficiencies in your horse’s diet.

RNA vaccines were tremendously successful during the Covid-19 pandemic due to excellent stimulation of immune responses combined with a fast and easy production process.

Traditional vaccines are typically based on subunit, inactivated or attenuated pathogens, which require long development times, making a rapid response to newly emerging pathogens difficult. In contrast, the RNA in RNA vaccines encodes the primary immunogenic protein(s) of the pathogen and can be developed quickly once the genetic sequence of a pathogen is known. This RNA is formulated or ‘packaged’ in lipid nanoparticles, cationic polymers, or hyperbranched polyglycerol (hPG) amines to allow for efficient transfer into host cells where the RNA of interest is translated into an immunogenic protein.

This protein then triggers an immune response against the very same protein expressed by the pathogen. Currently, RNA vaccines are being explored for a wide range of human and animal pathogens. The main advantages of RNA vaccines are that the production of RNA vaccines is technically simple, fast, easy-to-adapt, cost-effective and free of animal material.

There are currently two types of RNA vaccines, the conventional mRNA vaccine and self-amplifying (sa)RNA vaccines. The conventional formula contains a fixed concentration of packaged mRNA while saRNA vaccines may contain less target RNA than the conventional formula, but in addition contain a sequence encoding for an enzyme called ‘replicase,’ which amplifies the RNA sequence of interest, (i.e., itself). The advantage is a ‘smaller’ package with a longer duration of protein expression depending on the replicase half-life.

While vaccines for some pathogens are easy to design because there is only one, or few, immunologically important protein(s) for protection, other pathogens are more complex and require a multiple-target or cascade approach. This is one of the biggest limitations of RNA vaccines, as only a limited number of RNA sequences of interest – up to three – can be packaged into a single product or injection. Another disadvantage of RNA vaccines is storage, as most require storage at either -20°C or even at -80°C.

Equid alphaherpesvirus 1 (EHV-1) and 4 (EHV-4) are common equine viral pathogens. Horses in North America are routinely vaccinated against several viruses, including Western and Eastern Equine Encephalitis virus (WEEV, EEEV) and against West Nile virus, as well as equine influenza virus (EIV), with all of these vaccines performing reasonably well. In contrast, EHV-1 and EHV-4 outbreaks still occur in well-vaccinated populations. Thus, it is not surprising that the first efficacious nucleic acid vaccines have been developed against viruses for which protective immune responses can be induced with one (or few) immunogenic proteins, including coronavirus, flaviviruses and influenza viruses.

Unfortunately, EHV-1 and EHV-4 are not one of these viruses. Currently, challenges of developing effective mRNA or saRNA vaccines against equine herpes viral infections include the inherent antigenic complexity and immunosuppressive functions of EHV-1 and -4. With funding available through the Grayson Jockey Club Equine Research Foundation in Lexington, Kentucky, and in collaboration with Paul Lunn, BVSc, MS, PhD, MRCVS, Dipl. ACVIM, dean of the University of Liverpool’s School of Veterinary Science, in the U.K., and Juergen Richt, DVM, PhD, Director of Kansas State University’s Center of Excellence for Emerging and Zoonotic Animal Diseases (CEEZAD) and NIH COBRE Center on Emerging and Zoonotic Infectious Diseases (CEZID), in Manhattan, we are currently testing the safety and efficacy of EHV-1 mRNA and saRNA vaccines.

Based on previous experience, our vaccine prospects include nucleic acid sequences encoding EHV-1 glycoprotein D and the Immediate Early (IE) gene. The rationale is based on available results from previous studies with EHV-1, and ii) on the Shingrix® vaccine success story of a subunit vaccine that only contains the glycoprotein (g)E (analogous to EHV-1 gD) preventing shingles in adults after childhood varicella-zoster infection (chickenpox).

We expect these two components to be highly immunogenic, and to stimulate both cellular and humoral (antibodies) immunity. This project is ongoing, and we will provide updates on the progress. We anticipate that testing the vaccine in a neurological model of EHV-1 will show at least some protection from EHM which will be an improvement over currently available vaccines. In the future, this strategy can be further refined and tested for duration of immunity or effectiveness as a booster following vaccination with conventional vaccines. Because of the high sequence homology of the selected viral proteins, it is likely that this vaccine would also offer cross protection to EHV-4. Finally, once we can show the applicability of the technology for EHV-1 in horses, it could readily be adapted to other viral pathogens of horses.

Editor’s note: This is an excerpt from Equine Disease Quarterly, Vol. 34, Issue 1, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Lutz S. Goehring, DVM, MS, PhD, Wright – Markey Professor of equine infectious diseases at the University of Kentucky’s Gluck Equine Research Center, in Lexington, Gisela Soboll Hussey, DVM, PhD, professor at Michigan State University’s College of Veterinary Medicine, in East Lansing, and Klaus Osterrieder, Dipl. ECVM, dean of City University’s Jockey Club College of Veterinary Medicine and Life Sciences in Hong Kong, professor of virology and chair at Freie Universität, in Berlin, Germany, and adjunct professor of virology at Cornell University, in Ithaca, New York.

Rotavirus, a leading cause of diarrhea in foals, poses significant health risks from gastrointestinal upset to death, despite the availability of vaccines. Researchers at Texas A&M University, in College Station, along with scientists in
clinicians from other Texas institutions, recently studied an experimental mRNA-based vaccine that could offer better protection for foals.

Noah Cohen, VMD, MPH, PhD, Dipl. ACVIM-LA, distinguished professor and associate department head at Texas A&M’s College of Veterinary Medicine and Biomedical Sciences, presented the group’s findings at the 2024 American Association of Equine Practitioners Convention, held Dec. 7-11, in Orlando, Florida.

Understanding Equine Rotavirus Groups

Two distinct rotavirus groups cause diarrhea in foals: the long-recognized equine Group A rotavirus—ERVA, the microbe most frequently identified as a cause of diarrhea in foals—and the recently identified Group B rotavirus (ERVB) emerging in Central Kentucky, said Cohen. “While current vaccines, including the VP8 mRNA vaccine, target ERVA, they are not expected to protect against ERVB.”

Current Rotavirus Vaccine Limitations

In the U.S., veterinarians administer the existing rotavirus vaccine to pregnant mares in hopes of passing antibodies to foals at birth via colostrum, the first milk produced by the mare. “This killed virus vaccine has been the standard for decades, but its efficacy is increasingly questioned,” said Cohen.

In a recent study in Central Kentucky, researchers revealed that 83% of foals infected with either rotavirus strain were born to vaccinated mares, pushing veterinarians and scientists to seek more effective solutions, he added. Targeting the VP8 protein of ERVA—which acts as a surface spike protein responsible for attaching the virus to host cells—for vaccine development has shown promise in neutralizing the virus in humans, so Cohen’s team investigated its potential for equine applications.

Studying the New Rotavirus Vaccine

The researchers tested an mRNA-based vaccine targeting VP8 alongside the traditional vaccines in a controlled study involving 12 multiparous (having had more than one foal) mares and their foals. They divided the mares into four groups, receiving either one of the vaccines or no immunization (controls). They took blood samples before and after vaccination for the mares and on Days 1, 35, and 49 of life for foals.

Key Findings

• Mares:
  • Antibody levels in all groups were similar prior to vaccination.
  • The team observed a significant antibody increase post-vaccination only in the mares receiving the mRNA vaccine.
• Foals:
  • On Day 1, after colostrum intake, foals of mRNA-vaccinated mares exhibited significantly higher antibody levels than those in other groups.
  • By Day 49, foals of mRNA-vaccinated mares maintained these elevated antibody levels.
• Antibody efficacy:
  • The mRNA vaccine induced greater antibody activity against equine rotavirus A than the traditional vaccine.
  • Neutralizing antibodies produced after mRNA vaccination were effective against both G3 and G14 (Group A) rotavirus strains.
• Practical advantages:
  • Horses only need two injections of the mRNA vaccine, as opposed to three injections of existing vaccines.

Limitations and Future Directions

The researchers followed the mares and foals for a short period of time (49 days), though they didn’t measure antibody presence in mares’ milk, which could provide antibodies against the virus in the foals’ gastrointestinal tract. “Additionally, all mares except the controls had been previously vaccinated with the standard vaccine, meaning none were naive to the antigen,” said Cohen.

Despite these limitations, he said the results strongly suggest the mRNA vaccines are more effective at inducing long-lasting, viral-neutralizing antibodies in foals and, therefore, are likely to provide better protection than the current vaccines.

Take-Home Message

Cohen’s findings represent a significant step forward in preventing rotavirus-related diarrhea in foals. “This research highlights the potential of mRNA technology to address the limitations of current vaccines,” he said. “A better vaccine is crucial to reducing the prevalence of rotavirus in foals, and these results offer hope for a more effective solution.”

Scientists are discovering new applications for biologic therapies when treating wounds, ligament injuries, eye issues, and infertility in horses

Over the past quarter century equine practitioners have increasingly embraced regenerative therapies—techniques that restore, replace, or recreate cells, tissues, or organs to treat or mitigate disease—such as stem cells and platelet-rich plasma (PRP). They primarily reach for these therapies in the musculoskeletal arena, with research supporting their use for treating injuries to structures such as the superficial digital flexor tendon. 

Based on a review of the literature, however, several veterinary research teams believe the benefits of regenerative therapies can translate to tissues beyond tendons, ligaments, and joints. Although limited in numbers, those study results suggest veterinarians can also use regenerative therapies in the reproductive, wound care, and ophthalmologic settings. In this article we’ll summarize a handful of recent studies highlighting the potential use of stem cells and platelets in various equine tissues.

MSC Therapy for Suspensory Ligament Branch Desmitis

Suspensory ligament branch desmitis (SLBD) is a common injury causing lameness and decreased performance in Thoroughbred racehorses. This type of injury reportedly confers a poor prognosis for future racing, even if mild. Like other soft tissues, so-called “healed” ligaments are biomechanically inferior to normal, healthy ligaments, leaving them prone to reinjury.

“This is particularly important in Thoroughbreds, as the fetlock joint experiences marked extension during high-speed exercise, placing the SLB under a high amount of tensile load,” says Stefanie Hansen, DVM, MS, assistant professor of large animal surgery at Michigan State University’s College of Veterinary Medicine, in East Lansing.

Because researchers have shown stem cell use might reduce reinjury rates and improve the quality of tendon healing, Hansen and colleagues wanted to know if mesenchymal stem cell (MSC) therapy would have similar benefits in ligament injuries.

They retrospectively reviewed data from 69 Thoroughbreds treated with MSCs for SLBD. After diagnosing SLBD with clinical examination and ultrasonography, veterinarians treated all horses with 20 million allogeneic (collected from a horse that’s not the patient and stored) umbilical-blood-derived stem cells. Also at the time of diagnosis, they harvested bone marrow for stem cell isolation and expansion from each patient.

After initial treatment with allogeneic stem cells, the horses were treated every two to three weeks for a total of three or four times with the autologous (originating from the patient) bone-marrow-derived mesenchymal stem cells (BM-MSCs) in combination with a controlled rehabilitation program. Lameness and ultrasound exams determined when each horse could resume training.

Seventy-one percent of the study horses raced following MSC treatment. For the 20 horses that had raced prior to injury, 90% returned to racing, whereas only 63% of horses with no race history raced following MSC therapy. “We postulate that this lower percentage of racing after injury in horses with no prior racing experience may be partially related to normal attrition,” says Hansen.

“We unexpectedly found that more severe lesions (Grade III, IV) had a similar prognosis as less severe lesions (Grade I, II),” she adds. “One possible explanation could be that Grade III and IV lesions were also treated with percutaneous splitting of the ligament in conjunction with MSC therapy.”

Hansen says this finding gives veterinarians and horse owners some confidence in treating severe injuries and provides hope for the horse’s future athletic performance.

The median length of time to racing after injury was 378 days, with a wide range of 126 days to three years. “Thus, owners should therefore still expect a long layup following SLBD even when stem cell therapy is applied,” Hansen says.

And although the researchers did not record reinjury rates, the average career length of horses that raced following injury was 29.5 months, suggesting treated horses had some racing longevity.

“The current literature remains unclear on the full benefit of allogeneic stem cells; however, there is evidence of a potential benefit,” Hansen says. “This allows us to treat the injuries at the time of diagnosis, whereas autologous stem cells must be harvested and cultured prior to being available for treatments—a process that typically takes two to three weeks,” says Hansen.

Looking forward, she and her colleagues agree studies directly comparing MSC therapy to rest/rehabilitation alone would yield valuable information about the efficacy of MSCs. However, they note that giving horses R&R without additional therapies is usually not an acceptable option in the racehorse industry using client-owned horses. “Despite the inherent limitations associated with a retrospective study such as this, results demonstrated that MSC therapy is a viable treatment option of SLBD in Thoroughbreds,” Hansen says. “We hope that this study can serve as an initial benchmark for comparison to other treatment options

Extracellular Vesicles and PRP for Endometritis

In a recently published study Lange-­Consiglio et al. evaluated whether they could use amniotic (amnion is the thin inner layer of placental membranes sur­rounding a fetus) mesenchymal-derived extracellular vesicles (EVs) to prevent persistent post-breeding-induced endometritis. As a leading cause of decreased fertility, this condition also poses important economic implications.

Extracellular vesicles are double-layered vesicles that cultured stem cells secrete. They contain lipids, proteins, and genetic material believed to possess immunological and inflammation-modulating properties.

In this study the research team collected EVs from the medium of cultured amniotic mesenchymal stromal cells (AMSC-EVs) and combined them with the inseminating dose of spermatozoa prior to routine artificial insemination of eight mares with known susceptibility to this type of endometritis. An additional eight susceptible mares served as controls. Those mares were inseminated without the addition of AMSC-EVs.

Compared to the controls, mares receiving AMSC-EV-enriched sperm had significantly reduced neutrophil (a white blood cell type) infiltration, decreased intrauterine fluid accumulation, and altered inflammatory response following insemination. Fertility/pregnancy rates were higher in the AMSC-EV group (87.5%) than the control group (62.4%), but this difference did not reach statistical significance.

Study authors said these encouraging results warrant additional study and this treatment “could prevent the onset of persistent post-breeding-induced endometritis and avoid the alteration of the inflamed endometrium into fibrotic tissue, which is more susceptible to developing persistent endometritis and resulting in infertility,” making it useful for susceptible mares.

In a separate study Ghallab et al. (2023) examined how intrauterine administration of freshly prepared PRP affected the reproductive performance of Arabian broodmares. Of the 39 mares studied, 25 (61.5%) were diagnosed with endometritis. All 39 horses underwent uterine lavage on the first three days of estrus, then received 20 IU oxytocin as an ecbolic agent (to induce contractions that help evacuate fluid from the uterus). Nine mares serving as controls did not receive additional treatment, 15 mares received 20 milliliters of autologous PRP via intrauterine infusion six hours after natural breeding, and 15 mares received an intramuscular injection of the antibiotic enrofloxacin once daily for three days after breeding.

Endometrial thickness decreased in both the PRP and enrofloxacin groups and was lowest in the PRP group. Pregnancy rates at 30 days post-breeding were highest in the PRP group (70%) compared to the enrofloxacin (60%) and control (22%) groups. 

The study authors said PRP treatment following uterine lavage and administering ecbolic agents “significantly enhances the uterine environment for subsequent successful conception,” which might be attributed to PRP’s essential growth factors and their effects on injured tissues.

They therefore concluded that PRP appears to be “an effective, low-cost, safe therapy alternative for modulating abnormal inflammatory edema patterns of endometritis, as well as improving pregnancy rates and reproductive performance in treated mares.”

Equine Regenerative Medicine for Wound Healing

Also in 2023, Rebecca Harman, PhD, and others at Cornell University, in Ithaca, New York, reviewed available data on biologic therapies for healing horse wounds. Lead author Gerlinde R. Van de Walle, DVM, PhD, of the Baker Institute for Animal Health at Cornell’s College of Veterinary Medicine, explains the skin is the body’s largest organ, and treating skin wounds properly is integral for a horse’s overall health.

“This is particularly true for wounds affecting the distal (lower) limbs, a location with poor vascularization and oxygenation and little soft tissue,” she says. “Common complications for wounds in the distal limbs include extensive tissue loss and/or infection of the wounds, resulting in unrewarding treatment outcomes.

“The idea of using regenerative therapies is interesting because they have potential to simultaneously promote wound healing and reduce infectious burden,” she adds.

As summarized in the full-length article, in vitro (lab) research supports using peripheral-blood-derived MSCs and their secretome, consisting of bioactive factors MSCs secrete, in wound management.

“Mechanisms of action of the MSC secretome identified to date include promoting migration of dermal fibroblasts, promoting the formation of new blood vessels, and inhibiting the growth of various bacteria, including Escherichia coli and Staphylococcus aureus, even when present in biofilms,” Van de Walle says.

Harman adds that a handful of in vivo (in the live horse) studies exploring amnion, stem cells, and PRP have been published with variable yet overall positive results.

Results from one study support using equine amnion for bandaging certain distal wounds. In ponies, pinch grafts applied to full-thickness limb wounds were bandaged with amnion covered by an absorbent layer of gauze and elastic adhesive tape. Their median time to healing was significantly shorter (30 days) than that of a control group bandaged with nonadherent dressings covered with gauze and elastic adhesive wrap (39 days).

In another study researchers created wounds on nine horses and treated them with either amnion or live yeast covered with a nonadherent bandage. The rate of wound contraction and epithelialization did not differ between the groups; however, exuberant granulation tissue (aka proud flesh) severity was significantly less for amnion-treated wounds. It also took fewer days for wounds treated with amnion to completely heal. 

Several research groups have explored MSCs in wound management.

“Injected stem cells appear more beneficial than topical application,” says Van de Walle. “This finding is based on a study that found significantly decreased wound areas when injecting umbilical-cord-blood-derived MSCs in the wound margins versus applying these cells topically embedded in a fibrin gel.”

Harman et al. also described a study using oral-mucosa-derived MSCs or their secretome mixed in a hyaluronic acid (HA) gel topically applied to surgically induced wounds on the thorax and forelimbs. Both HA mixtures (i.e., with MSCs or the secretome) had a positive effect on healing compared to the untreated control groups and the horses treated with HA alone.

Finally, PRP appears to hold great promise for promoting and supporting wound healing. In one of the many studies Harman et al. cite, they relayed data by Pereira et al. (2019), who evaluated various PRP preparations administered topically or injected into surgically created distal limb wounds.

“Key findings were that healing time was reduced in all PRP groups compared to controls, less granulation tissue was noted in the treatment groups, and the PRP gel had the most positive effects on wound healing,” says Van de Walle. “Overall, that study concluded that all of the studied PRP preparations positively affected healing and, thus, warrant further exploration.”

Conjunctival Stem Cells for Immune-Mediated Keratitis

Immune-mediated keratitis (IMMK) is a nonulcerative, nonpainful keratitis characterized by various degrees of corneal vascularization and opacification. The condition doesn’t typically lead to eye loss but might impair vision due to scarring, secondary infections, and diffuse corneal edema.

“IMMK is an increasingly diagnosed disease, which generally is well controlled by standard topical eye medication, such as cyclosporine,” says Brian Gilger, DVM, MSc, Dipl. ACVO, a professor at North Carolina State University’s College of Veterinary Medicine, in Raleigh. “But in many cases IMMK therapy either quits working or the IMMK is not responsive, leading to the need for new treatments.”

Therapy is typically long-term and, as many owners have learned firsthand, chronic ophthalmic therapy can be difficult in horses.

Because BM-MSCs modulate the immune system by downregulating inflammation, Gilger’s research team evaluated the efficacy of these cells for treating IMMK in a series of four horses (Davis et al., 2019).

Veterinarians administered autologous subconjunctival BM-MSC injections in all horses every three to four weeks for one to five treatments. Horses were maintained on a standard medical treatment regimen throughout the BM-MSC treatment period.

“These BM-MSCs are identical to those used in orthopedic applications,” Gilger notes. “And the injections are made with the horse lightly tranquilized, allowing the horse to return to normal activity within hours of the procedure.”

Three horses had increased corneal clarity, decreased neovascularization (new blood vessel growth, which can cause vision loss), and reduced surface irregularity. Only one of the treated horses was not responsive to subconjunctival BM-MSC therapy.

“These experimental results demonstrate the safety and potential efficacy of an innovative solution for IMMK,” says Gilger. “Subconjunctival autologous BM-MSCs can currently be used in clinical patients. Our current research is focused on determining if the cells themselves migrate to the area of inflammation or if they stay locally and secrete mediators to modulate the immune system. We are also examining the use of MSCs in other diseases, such as equine recurrent uveitis.”

Future Directions in Equine Regenerative Medicine

More than 25 years after equine veterinarians started using regenerative therapies, we are still scratching the surface of what they can do. Considering the power these therapies pack, they certainly warrant funding for additional well-designed and -controlled in vitro and in vivo studies. The many avenues that need to be explored include delivery methods and ways to produce the various therapeutic products. “Another exciting avenue of regenerative therapies is their potential as an adjunct or replacement for antibiotics,” says Van de Walle. Antibiotic overuse can lead to antimicrobial resistance—a potential health threat to humans and animals. The prospective of promoting tissue healing while also fighting bacterial infections is promising, particularly in wound ­management.”

Editor’s Note: This article originally appeared in the 2023 Research Roundup issue of The Horse: Your Guide to Equine Health Care.

How to decide if your older mare is a good candidate for breeding and improve her chances of success

Gala Argent wanted one last foal. After 25 years breeding Foundation Appaloosas, the educator and researcher had decided to retire from breeding. To mark the end of that era, Argent chose to breed her cherished homebred mare Della. Beautiful inside and out, the leopard roan was born on Argent’s Batavia, Illinois, farm two decades earlier.

Della might have been a senior mare, but she was in excellent health, Argent says. Like her dam and sire—who lived to be 28 and 30—Della was fit, energetic, and pain-free in her golden years. Plus, she’d already foaled twice with no ­complications.

After three months at pasture in a domestic harem with a leopard stallion, Della was in foal. Nearly a full year later, at age 21, she gave birth to the biggest and most precocious foal Argent had ever seen. Scooter was standing and suckling the senior dam’s full udder within minutes, she says.

While Argent’s story had a positive outcome, the reality is it’s not always easy to breed older mares, and there’s a higher risk of complications, our sources say. In this article we’ll share expert advice on how to decide if your older mare is a good candidate for breeding and how to improve her chances of success.

15 Years & the Reproductive Plateau

Up until about age 15, healthy mares have a 50-60% chance of conceiving per estrous cycle, says Patrick McCue, DVM, PhD, Dipl. ACT, a professor of theriogenology in the College of Veterinary Medicine & Biomedical Sciences at Colorado State University (CSU), in Fort Collins.

The ability to conceive and produce a live, healthy foal declines steadily starting at age 15 and decreases even more after age 20, he says.

That’s mostly because of an aging, scarred, infection-prone uterus, says Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute for Equine Science, in Neustadt, Germany. While some mares experience ovarian senescence, a gradual decline in the ability to produce fully functional oocytes, and stop cycling at around age 25, most continue to ovulate and produce good-quality eggs that then migrate into a poorer-quality uterus. 

Getting these mares pregnant often requires extensive veterinary assistance, Aurich says. Once pregnant, they’re more likely to develop uterine infections and abort. At foaling, they have an increased risk of uterine arterial rupture, due to aging blood vessels, and a retained placenta. And if it’s the mare’s first foal, it’s likely to be small.

For these reasons, the first step in breeding an old mare is assessing whether it’s right for her, she says.

Take an Honest Look at the Mare

If you want to breed your senior mare, take an honest look at her—not as the horse she used to be, but as the horse she is today.

“It’s not always a question of when she was born, but of her biological age,” Aurich says. “Does she look like a fit, healthy mare? Or is she losing body condition and having problems moving or getting up and down?” These are particularly important questions when considering the extra 250 pounds she’ll be carrying between the foal, placenta, and fluids and that she’ll be a full year older by the time she foals.

Non-steroidal anti-inflammatory drugs (NSAIDs) can help relieve arthritic pain during those final, hardest months of pregnancy without harming the foal, Aurich says. “But if you say you have to do it from the beginning of the pregnancy, I wouldn’t breed that mare,” she says.

Owners should also exclude mares with significant lameness, musculoskeletal injuries, or chronic laminitis from their breeding program, McCue adds.

Mares with pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease) might be poor candidates for breeding due to treatment with pergolide, Aurich adds. As a dopamine receptor agonist, pergolide can reduce fertility and interfere with colostrum and milk production.

Even so, stopping pergolide treatment one month before the anticipated foaling date might restore lactation potential, and owners can plan to provide donated, frozen-thawed colostrum at foaling, McCue adds.

Owners should check their senior mares’ reproductive anatomy for telltale signs of perineal aging, in which the vulva forms a sort of horizontal “shelf” under the anus. In such cases fecal material can enter the vestibule or vagina, urine might pool inside the vaginal vault, and mares might aspirate air into their reproductive tract. Owners can also check muscular tone by using two fingers to gently spread the vulva open.

“If it opens easily with minimal pressure, that’s indicative of less muscular tone,” McCue says. Poor muscular tone can also allow air and fecal matter to aspirate into the reproductive tract. The resulting trapped bacteria—and that from pooled urine or aspirated air—put the mare at risk of uterine infections, which are incompatible with conceiving and maintaining pregnancy without active treatment, he says.

Strongly Consider Foaling History

Older mares that have foaled in the past—even once— have a more mature reproductive system than older maiden mares that have never been bred, our sources say.

“It makes a big difference in potential outcome and prognosis for getting a mare pregnant,” McCue says.

Maiden senior mares—often retired performance horses whose owners now hope to start breeding—usually have “old maiden mare syndrome,” explains Aurich. That’s marked by an immature uterus that’s likely to produce a relatively small foal over a long gestation period—often a full year, she says. These mares also have a tight cervix that blocks the natural passage of fluids during a breeding cycle. That means the semen, bacteria, and other breeding-related debris that enter the uterus during ­breeding—whether through live cover or artificial insemination—can’t get expulsed afterward. As a result, inflammatory fluids pool in the uterus, interfering with both conception and pregnancy.

In addition, older maiden mares might struggle with their pregnancy weight, she explains. “They have to get used to getting heavier and to having problems getting up and lying down,” she says, especially if the mare has arthritic joints. Plus, they’re more prone to stress if they’re new to breeding and undergoing multiple invasive procedures over several months. “Then maybe she finally gets pregnant late in the season, and that means she’s late pregnant the following July or August when it’s hot outside,” she says. “That may be difficult for her circulation, thermoregulation, and everything. It’s much tougher.”

Seasoned broodmares, by contrast, have already benefited from “the whole endocrinology of pregnancy” that includes the activation of glands (and hormone release), muscles, and other tissues that favor reproduction, McCue says. The foaling process itself also exercises the cervix, which opens fully and then pulls closed again. For healthy breeding, “it’s good to maintain that dynamic cervical function,” he says.

And if the mare has foaled in the past year, she’s more likely to conceive again relatively quickly, he adds.

Still, if an experienced broodmare has become more difficult to get or keep pregnant, it’s probably time to retire her rather than trying for one last foal, Aurich says.

Get a Thorough Clinical Exam

Breeding exams start with a confirmation of what the owners might have already observed themselves, making sure their senior mares have the overall physical health, musculoskeletal stamina, and body condition to support a year and a half of pregnancy and lactation, our sources say. Veterinarians will then assess the mare’s perineal anatomy and inspect the vagina with a speculum to identify pathological conditions such as scars in the cervix (that might have occurred during the previous foaling) or varicose veins that might develop in aging mares, Aurich says. They can also use a gloved hand to digitally evaluate the cervix.

Uterine ultrasounds and biopsies can help the veterinarian determine the degree to which the lining of the uterus—the ­endometrium—is still healthy and functional, she explains.

Endometrial glands produce a substance called histotroph, which provides nutrition to the developing embryo. Aurich says fibrous scar tissue often develops in the uterus of older mares, compromising those glands.

Ultrasound can reveal lymphatic cysts, which result from scar tissue deposition, says McCue. While small lymphatic cysts are relatively harmless, growth in size and number can indicate more severe endometrial scarring as well as a proliferation of microscopic glandular cysts, which compromise endometrial function.

Biopsies can confirm the presence of microscopic glandular cysts, he says. They also reveal age-related inflammatory cells or damage to uterine glands. Veterinarians grade biopsy results from Grade 1 (healthy) to 2 and 3 (moderate and severe pathologies affecting fertility).

Combined, these results can provide a prognosis for breeding success and guide decision-making, our sources say.

Manage for Optimal Fertility

Mares should be up to date on the American Association of Equine ­Practitioners’ core vaccinations—rabies, tetanus, West Nile virus, and Eastern and Western equine ­encephalomyelitis—as well as locally relevant risk-based vaccines. Vaccinations should be given at least 30 days prior to active breeding to allow for an appropriate immune response, McCue says.

Maintaining good dental care is critical in older horses but even more so in older broodmares because they’ll be eating for two, he says.

Because pregnant mares’ bodies prioritize the growing fetus, broodmares are at risk of losing body condition during pregnancy and lactation—“one of the highest nutritional demands on any horse,” McCue says.

Older horses often struggle to maintain body weight, so senior mares must start the breeding season in good body condition or even mildly overweight if their metabolic health allows it, says Aurich.

Older, metabolically healthy mares should be fed high-protein and calorie-rich forage, such as first-cut meadow hay or a combination with alfalfa, supplemented with concentrated feeds as needed, she says.

Recent research at CSU suggests diets rich in omega-3 fatty acids and antioxidants help oocytes metabolize energy and mature more efficiently, especially in senior mares. Therefore, supplementing with omega-3 fatty acids might be helpful, McCue says.

Finally, manage older mares to start cycling as early in the year as possible, he says. Older mares naturally start cycling as late as May or June and tend to have longer intervals between cycles due to slower ovarian follicle development. “I would recommend housing older mares under lights (or using blue-light therapy hoods) beginning on about Dec. 1 to advance the first ovulation of the year to mid-February so you have multiple opportunities to breed her,” he says.

Breed With Planning, Patience, and Assistance

For older mares McCue recommends selecting stallions with high fertility rates.

While live cover can be effective, breeders can also choose artificial insemination (AI). Fresh semen that is collected, processed, and inseminated within hours of collection often provides the highest pregnancy rates, he explains, though cooled storage can offer similar fertility rates for many stallions. By contrast, pregnancy rates using frozen semen are frequently 10 to 20% lower than with fresh or cooled semen. Even so, it’s still an acceptable option for breeding older mares, he says.

Regular transrectal ultrasound exams can reveal exactly when older mares are about to ovulate, says McCue. This helps you time insemination as closely as possible to ovulation, which improves conception rates. If needed, veterinarians can administer an ovulation-inducing agent, such as human chorionic gonadotropin or deslorelin, to help ensure timeliness. Follow-up ultrasounds can confirm ovulation has occurred and show whether the mare is collecting inflammatory post-breeding fluid, which oxytocin administration can often eliminate. 

Once bred, mares with poor perineal conformation should undergo a Caslick’s procedure. Also called a vulvoplasty, the procedure closes the top part of the vulva to prevent aspiration of air and bacteria as a protective mechanism against uterine infection during pregnancy, McCue explains.

Aurich says she recommends a daily dose of altrenogest starting the fifth day after ovulation to compensate for low ­progesterone—the hormone that prepares the uterus for pregnancy. “The corpus luteum function may be compromised, for example, because of the inflammatory response of the uterus to breeding, but it is also possible that older mares need more progesterone because of the ‘scarred’ endometrium,” she says. The corpus luteum is the structure formed after the ovarian follicle releases the egg; it produces progesterone.

Consider Embryo Transfer or ICSI

Older mares that are poor candidates for conceiving and carrying a pregnancy can still reproduce through advanced reproductive techniques such as embryo transfer and intracytoplasmic sperm injection (ICSI), Aurich says.

The relatively good quality of older mares’ eggs makes them good candidates for these assisted reproduction techniques, she explains.

If the mare’s endometrium and uterus are healthy enough to maintain a free-floating fertilized egg and growing embryo for at least eight days, she can undergo precisely timed AI and then have her uterus flushed to recover the embryo. That embryo then gets transferred into a younger surrogate that carries the foal to term and nurses it.

For old mares that can’t successfully conceive, scientists can harvest their eggs and perform ICSI in a laboratory before transferring embryos into surrogate mares.

An added advantage of these techniques is they allow for multiple foals from the same aging mare at the same time, in different surrogates, she says. You can even freeze and store the eggs long-term.

“If you have a mare that’s getting old and you really like her, you can actually harvest her eggs or embryos and then produce the foals at a later time,” Aurich says.

Take-Home Message

Owners can increase their chances of successfully breeding their old mares by recognizing the ones that make the best candidates, managing them appropriately, and providing the necessary therapeutic assistance, our sources say. When making decisions about breeding a beloved aging mare, it’s important to consider her health and welfare as well as the financial risks. When the mare’s general or reproductive health can’t support a pregnancy, her eggs can still be used for ICSI and/or embryo transfer into a younger surrogate.

Q.When do I start my foal on an exercise program? My show jumper just gave birth to a foal a couple of weeks ago, and I want to give him every advantage possible since I have plans for him to be my next jumper. What type of exercise should I start him with, and when?

A.An exercise program designed to build muscle mass is not recommended for the first year because the skeletal system of the foal is just not ready to handle a huge amount of muscle. It is still developing. If you put too much muscle on this immature framework, problems like arthritis, flexural deformities, and angular limb deformities can occur. These are all results of too much muscle mass on a skeletal system that is not yet ready to handle it. The best way to avoid these problems is to avoid a rigorous exercise program until the foal matures past a year old.

Halter-breaking and some (ground work with) foals is not bad; it will help the foal learn some manners. It’s the rigorous exercise program that causes problems.

It is important that the newborn foal gets exercise, but at its own pace. The foal will benefit from the fresh air of being outside, which will reduce its chances of contracting a respiratory infection. Studies have shown that stallbound foals are affected by the ammonia content in the air. The musculoskeletal system in terms of bones, muscles, and cartilage also will benefit from the exercise the foal gets when it is turned out.

A good introduction to exercise for the new foal is to begin by putting it and its dam out with one or two more mares and their foals. This should begin one to two days after birth, gradually increasing the time spent outside each day. By two weeks of age the foal should be able to spend up to a full day in the field. Only place mares and foals together that are compatible—some mares are not compatible with other’s foals.

Something else to keep in mind, depending on where you live, is the climate. Very young foals in cold climates should be turned out for short periods at a time so they can become acclimated to the cold. Or, if you are in a warm climate, sunburn is a concern that needs to be dealt with when managing the foal’s time outside.

While the benefits outweigh the risks of normal exercise, there are some potential problems to watch out for. First, you should make sure the foal does not over-indulge in exercise. Many dams, especially younger ones, have the tendency to run at full speed in the field, and their foals have trouble keeping up. Dams with this behavior should be turned out in smaller pens so their foals can keep up with them without overdoing it.

Pay attention to physical dangers like holes in the field, downed branches, bad boards on fences, etc. Any of these can spell disaster for the young foal, so precautions should be taken. It is a good idea to inspect the field in which the foals will be turned out in order to minimize the risks.

Once the foal is weaned from the mare, it can be turned out with other foals around the same age. It is important to keep foals grouped by age, and also by sex, as they reach yearling age. Age grouping is important because if you put older foals with younger ones, then the younger ones will have a hard time keeping up with the older foals. The older foals also might show some aggression toward the younger ones. Grouping by sex is to keep the more aggressive colts away from the fillies. Colts tend to become a little aggressive as they approach yearling age.

Some signs that indicate the foal is getting too much exercise include lameness and changes in the conformation of the legs, which might be angular limb deformities, or flexural deformities that makes the foal look calf-kneed or buck-kneed. These problems are the result of a combination of growing too fast and too much exercise. The foals which show these deformities need analgesics and controlled exercise.

Exercise is definitely good for foals, but foals have very “plastic” bones at early ages and that should be taken into consideration. Controlled exercise is the key.

As we head into winter, many broodmare owners and managers start thinking about warmer weather and the arrival of a new crop of foals. But before the late nights and early mornings of foal watch ensue, we must consider the dietary needs of those mares and how they change during late gestation. As the adage goes, “She’s eating for two.”

As the mare progresses into her final “trimester,” or the last three to four months of pregnancy, we need to start increasing her nutritional plane. It is during this last phase of pregnancy that we observe the most fetal growth, at approximately 1 pound per day. A mare must consume enough nutrients to meet her needs as well as those of the fetus and, in the latter weeks, to support mammary development. If a mare is due while the temperatures are still cold, she will also have increased nutritional demands for thermoregulation. Nutrient requirements for calories (energy), protein, calcium, and phosphorus will increase.

Body Condition

We should be familiar with the appropriate weight and body condition of our mares. Most feed companies have nutritionists on staff who can visit your farm and assess your mares. Many have a portable scale they can bring along to weigh your mares. They can also assess body condition while weighing to make sure your mares are neither too fat nor too thin. Having the mare in moderate to fleshy condition will give her some fat reserves for foaling and early lactation. Weight gain of 140 to 200 pounds is common.

Forage

We must also ensure our mares receive adequate forage. Forage provides the mare with not only nutrients but also heat when her body ferments/digests it in the hindgut. This process can help the mare maintain core body temperature during colder months. Oftentimes weight loss during winter is due to the horse trying to maintain body temperature. We want our mares to receive at least 1% of their body weight (or about 10 pounds of hay for the average 1,000-pound mare) in good-quality forage per day. The mare might be able to meet her dietary needs with good-quality forage alone, at an amount of 2-3% of body weight, or 20 to 30 pounds of dry forage. As the mare progresses into late gestation, the growing fetus takes up more room in the abdomen, and the mare might not be able to eat enough forage to meet her needs. Adding a concentrate designed for pregnant mares can help. To ensure you are meeting dietary requirements, follow the directions on the feed tag. Feeding less of a concentrate than what is recommended on the tag can lead to nutritional imbalances or deficiencies.

When we are looking at forage types, we want to make sure the hay is of good quality. A mostly grass hay with some legume content, in addition to concentrate feed, will likely meet most of the mare’s needs in late gestation. Avoid endophyte-infected tall fescue. Consumption of this forage can cause a variety of complications in the late-gestation mare, including low or no milk production, delayed parturition, retained placenta, and a dysmature foal.

Water

Water intake requirements also increase during late gestation as the mare drinks to meet her needs (about 1 gallon per 100 pounds of body weight) and for fetal development. An average 1,000-pound broodmare needs 10 gallons to meet her water requirements but could need an additional 5 gallons for the fetus. Water intake is especially important when most of the diet is dry feedstuffs, such as hay and grain (as opposed to pasture), to help prevent colic.

In summary, make sure the late-gestation mare is receiving enough nutrients to meet both her needs and the needs of the developing fetus. Monitor energy, protein, calcium, and phosphorus levels in her diet, and ensure she has access to good-quality forage and water.

Better understand this common—and frustrating—condition seen in horses

He’s just a little off. It’s hard to say exactly what’s going on. But he’s your horse, and you know him so well you pick up on the slightest little nuances when something is wrong.

So, you check him all over: no signs of injury, no strange bug bites, no drainage coming out of the nose, no diarrhea, no cough. Then you take his temperature.

Sure enough, fever. Something is wrong. But what?

Welcome to the world of fever of unknown origin. For both owners and their treating veterinarians, this condition can be fraught with frustration, confusion, guesswork, and a Sherlock-Holmes-like investigative process with some modern technological flair.

Fortunately, through strong collaborations with laboratories and referral clinics, horses with fevers of unknown origin can often get the diagnoses and targeted treatment they need.

“At first, it’s unknown origin—but we hope to give it an origin, and give that horse a diagnosis,” says Toby Pinn-Woodcock, DVM, Dipl. ACVIM, assistant clinical professor in the Department of Population Medicine and Diagnostic Sciences at Cornell University College of Veterinary Medicine, in Ithaca, New York.

Understanding Fever in Horses

More than ever, horse owners are tracking their horses’ body temperatures, our sources say.

Technology has certainly played a role in that—thanks to rubbery digital thermometers that beep with a digital reading less than 30 seconds after being inserted in the horse’s rectum. Veterinarians can also now implant microchips with temperature sensors into a horse’s neck, which send real-time data to mobile phones and alert you if the temperature is abnormal.

When such technology meets the hands of highly observant owners, fevers get noticed right away. “Horse owners are so astute,” Pinn-Woodcock says. “They catch things so early—sometimes before there are other signs.”

Rectal or chip-based temperature readings above 101.5 degrees Farenheit (38.5 degrees Celsius) generally indicate a fever in horses. Unless extenuating circumstances exist—such as excessively high outdoor temperatures or significant muscular effort akin to race training—that means there’s some sort of inflammation in the body, says Julia Felippe, MedVet, MS, PhD, Dipl. ACVIM, professor and immunologist in the section of Large Animal Medicine, also at Cornell.

Fever and inflammation function as the body’s first-line defense mechanisms in response to a wide range of health challenges, she says. Specialized molecules induce fever to help immune cells move and function better, while also creating an unfavorable environment for pathogens (disease-causing organisms) to survive.

Indeed, sometimes owners catch fevers before other clinical signs develop, such as nasal discharge, coughing, or diarrhea. Those additional signs often help pinpoint the fever’s cause within a few days, our sources say. But not all horses develop additional signs, even in the case of infectious diseases. 

If an acute fever goes away on its own and stays away, it’s still useful to find out its cause—not only to keep the horse’s medical history current and accurate but also determine whether the fever stems from a contagious disease.

But if fevers persist, or come and go, without any clear reason, Pinn-Woodcock recommends finding out what’s behind them, because they can indicate life-threatening diseases.

First Things First: Biosecurity at the Farm

Until you can prove otherwise, assume any fever of unknown origin might stem from a pathogen that could spread to other horses. That means you need to ramp up biosecurity immediately.

Your feverish horse should go in an isolated stall or paddock where he has no contact and shares neither air space nor water sources with other horses, our sources say. “The next step is to contact your veterinarian for evaluation and advice,” says Felippe. If you get a diagnosis for an infectious disease, you’ll need to follow the biosecurity guidelines specific for that disease to prevent or stop an outbreak.

Keep the horse in isolation while you work with your veterinarian to rule out contagious causes of equine fever common to your region, Pinn-Woodcock says.

Causes of Fever in Horses

A feverish horse could have a wide range of bacterial or viral infections, such as strangles, equine herpesvirus types 1 and 4 (EHV-1 and EHV-4), the tickborne disease anaplasmosis (caused by Anaplasma phagocytophilum bacteria), and equine coronavirus—which are a few of the common culprits, our sources say. But they could also carry fungal or parasitic infections such as guttural pouch mycosis and piroplasmosis. Noninfectious conditions, including cancer, immune-mediated disease, or an immunodeficiency disorder, could also be to blame.

“It can be quite challenging to find the cause of fever,” Felippe says.

Cornell’s Animal Health Diagnostic Center (AHDC) offers a comprehensive plan for homing in on horses’ fevers of unknown origin in more complex cases, says Pinn-Woodcock. The Cornell AHDC provides a long list of possible causes of equine fever and diagnostic tests that can be tailored to specific circumstances. These include cultures and polymerase chain reaction (PCR) tests on whole blood, nasal swabs, cerebrospinal fluid, peritoneal (abdominal) fluid, urine, and feces for pathogens such as herpesviruses, West Nile virus, coronavirus, adenovirus, strangles, Salmonella, Lawsonia, Leptospira, and more.

That doesn’t mean people should run all these tests, she says. Rather, the comprehensive plan serves as a “brainstorming tool” for practitioners. “It’s kind of a jumping-off point to select tests a la carte given the context of each case,” she explains.

Clues for Fever: Seasons, Regions, and Travel

The hunt for a fever’s origin starts with certain clues, our sources say.

Seasons, for example, play an important role, notes Pinn-Woodcock. “We tend to see more fevers caused by betacoronavirus in the winter months, as this virus survives best in cool, moist environments, and we tend to see respiratory viruses in the early spring, which may be due to increased horse travel during this time of year,” she says.

Region also plays an important role, she explains, especially regarding vector-borne diseases. Vectors are disease transmitters—think ticks and midges. Different regions of the world have different vectors. In the northeastern U.S., for example, equine granulocytic anaplasmosis commonly causes fever in horses—especially in the fall when the ticks carrying A. phagocytophilum bacteria are more prone to bite large mammals. And Potomac horse fever, caused by the Neorickettsia risticii bacteria harbored by aquatic insects such as mayflies and caddisflies, occurs most often in summer to early fall in horses living in proximity to a lake, pond, or river in some regions of the U.S. and Canada. Eastern equine encephalitis (EEE) can cause fever in southeastern and Gulf coast states year-round and in northeastern states during summer and early fall when mosquitoes are present.

Make sure you also consider the horse’s recent travel history, says Pinn-Woodcock. Horses attending shows or other events involving multiple horses from different origins can contract a wide variety of pathogens such as respiratory viruses, she says. Plus, researchers have recently confirmed horses in transit often have slightly weakened immune systems, making them more susceptible to such pathogens.

The travel history of the horse’s stablemates should be considered as well, she adds. Horses that have recently arrived on the premises or have been out traveling and returned home could have brought pathogens with them—without appearing sick themselves. “There’s a lot that goes into these risk analyses,” Pinn-Woodcock says.

The Veterinarian’s Workup on Fever

Workups for fevers of unknown origin start with a detailed history, followed by a thorough clinical exam of each system in affected horses: respiratory, gastrointestinal, musculoskeletal, urogenital, and so on, Felippe says. “You use a multidirectional approach to narrow it down,” she says.

Based on the observations, vets collect diagnostic specimens such as nasal swabs, blood samples, and possibly peritoneal or cerebrospinal fluid for laboratory analyses. They might also analyze the feces for equine coronavirus or infectious bacteria such as Salmonella or Clostridium, which cause intestinal disease.

Our sources say that while these samples can be used for specific disease testing based on the case context, complete blood counts (CBCs) and complete serum chemistry profiles can also provide clues. These comprehensive exams can point to trends and even specific organ systems that might be affected, based on values that are within normal range or not. For example, high levels of the enzymes aspartate transaminase (AST) and gamma-glutamyl transferase (GGT) suggest a liver problem, and elevated blood urea nitrogen (BUN) and creatinine point to kidney issues.

“This can be a great place to detect a hint about what’s going on,” Pinn-Woodcock says.

Finally, additional tests might include imaging such as X ray or ultrasound, checking for evidence of inflammation or infection in various internal organs.

Even so, test results themselves don’t necessarily give a definitive answer, says Felippe. Tests might return negative results if the active pathogen shedding and replication period has passed, for example. Positives could represent remnants from previous infection or exposure that aren’t the cause of the current fever, or they could be an inflammatory response to vaccination.

“The veterinarian really has to understand what the results mean and how valid they are,” she says. “Even a positive result needs to be interpreted within the case context.”

On the opposite end of the spectrum, test results might not show anything at all—at least, not initially. “Fevers of unknown origin can sometimes take multiple rounds of testing,” Pinn-Woodcock says. “It’s a process. It can take time for the veterinarian to get to the bottom of it—and patience on everyone’s part. It’s not always straightforward.”

Dedicated Fever-of-Unknown-Origin Test Panels

Within a year of arriving at Cornell’s laboratory, Pinn-Woodcock realized her team was getting lots of calls from equine practitioners seeking help for diagnosing horses with fevers without other clinical signs. “It was confusing for them to figure out what sample types they needed and which tests to request,” she recalls.

So, in 2019 she developed a dedicated fever-of-unknown-origin test panel targeting the most common causes—at least in the northeastern U.S. The panel streamlines the testing process, eliminates confusion, and aids efficiency, leading to faster answers and cheaper costs, she says. The Cornell panel provides results on 10 pathogens within three days. This makes it easier for veterinarians to screen their patients for all these things to help them figure out a treatment plan, Pinn-Woodcock says.

University of California Davis researchers have also developed a fever-of-unknown-origin panel adapted to the western U.S., she adds. Regardless of where veterinarians are, they can ship samples to these labs or use existing panels as models to create their own lists of tests to order from local diagnostic labs.

Still, these dedicated panels don’t cover everything, Pinn-Woodcock adds. They just make it easy to rule out the most common infectious causes. “There are many other causes of fever,” she says.

Recurrent Fevers and Immune Disorders in Horses

Horses affected by fevers that just never seem to go away, or keep coming back after treatment, might have an immune disorder, Felippe says. In her research she’s shown these disorders can be particularly difficult to diagnose due to the immune system’s various cell types and functions, she says. “You could have something that affects one area of the immune system but not the other areas,” she explains. “And we do not have tests for all areas of the immune system, so we can miss the real cause.”

Still, some tests can be “quite revealing,” she adds. Low concentrations of immunoglobulins M and G (IgM and IgG) in a horse’s blood, for example, indicate impaired antibody production. “These horses have a decreased capacity to produce enough antibodies to fight against diseases, making them highly susceptible to various pathogens all the time,” she explains.

The immune system can also overreact, creating exaggerated immune responses, Felippe says. Such immune hypersensitivity leads to frequent fevers and tissue inflammation. “It’s a bit antagonistic,” she says. “The immune system is to use its cells and mediators for protection, while losing control of itself and causing damage.”

Take-Home Message

Fevers flag a health problem, but without other clinical signs it can be tricky to determine what that problem is. Using clues such as season, region, and recent travel history can help narrow down the possibilities, and certain diagnostic labs offer dedicated test panels that can help veterinarians efficiently diagnose—or rule out—the most common causes. Our sources indicate that with hundreds of infectious and noninfectious causes for fevers, identifying the issue often demands time and patience. Diligent, collaborative work among horse owners, vets, and laboratories frequently leads to proper diagnoses and targeted treatment. 

This article is from the Winter 2024 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Q: Is it okay to feed my horse peppermints and sugar cubes? I’m concerned about the amount of sugar they contain. If it is okay, how many is too many?

A: Simple sugars, such as the sucrose found in peppermints and sugar cubes, are absorbed by the horse’s small intestine as glucose and fructose. Glucose causes release of insulin to facilitate the entry of glucose in to cells. Fructose (not to be confused with fructans) is metabolized differently. Only metabolized in the liver, fructose is more lipogenic than glucose, meaning that it’s more likely to lead to production of fat.

Most concern about sugar and starch intake has stemmed from our increasing knowledge about insulin resistance (IR), laminitis, polysaccharide storage myopathies (PSSM), and equine gastric ulcer syndrome (EGUS). Horses with IR release more insulin than is normal in order to remove glucose from their blood stream. As a result, while circulating glucose tends to be normal, circulating insulin is elevated. High circulating insulin creates an increased risk for developing laminitis. Horses with PSSM store glycogen (the storage form of glucose) abnormally in their muscle tissue, and diets high in starch and sugar cause increased production of volatile fatty acids in the gastric stomach causing a more acidic environment and a greater likelihood of a horse developing EGUS

I think it’s important to put the questions of sugar in treats in perspective of a horse’s typical daily non-structural carbohydrate consumption. If we assume a 1,200-pound horse eating 2% of body weight as dry matter from hay a day, and that the hay contains 10% moisture and 10 % nonstructural carbohydrate (NSC) on a dry-matter basis (a value often used as the recommended upper NSC level for horses with metabolic issues, such as IR and PSSM), this horse is consuming 1,090 grams of NSC (starch and simple sugars) per day.

A pure sugar cube weighing about 4 grams is 100% sucrose. The popular round, red-and-white peppermint candies have a human serving size of three pieces (about 15 grams) and of that between 8 and 10 grams are sugar. Traditional peppermint candy canes are heavier at 18 grams and provide about 12 to 14 grams of sugar. You can see that in the context of the above horse’s daily diet these are tiny intakes of sugar. However, there are some important considerations.

When feeding a horse hay, you’re also feeding it proteins and minerals that help buffer stomach acid. Additionally, hay’s fiber component impacts the rate at which the NSC reaches the small intestine and is absorbed. The sugar in sugar cubes dissolves quickly and will move with the liquid fraction of the digesta, which moves more rapidly than larger fibrous particles. This means that that the sugar will likely be absorbed relatively soon after it is fed. This makes it potentially more likely to cause a spike in blood glucose than the NSC contained within hay.

Feeding a healthy horse three or four sugar cubes is unlikely to cause a significant glucose spike; however, for a horse with uncontrolled IR, PSSM, or a laminitis history, feeding sugar cubes isn’t a risk worth taking. Skip the sugary treats, too, if your horse is overweight, especially if he has a cresty neck. After all, every calorie counts and calories from treats mean feeding fewer calories from “real” food. Human research shows that tissues in insulin resistant people are more sensitive to insulin after exercise. This may or may not be the case in horses, but if it is, then your horse might be better able to handle the sugar in these treats when they are given shortly after work.

For the otherwise healthy horse, consuming a candy cane or a few peppermint candies is unlikely to have any major impact.

Pioneering methods in equine reproduction offer horse owners unprecedented control and flexibility

Want to show your mare and breed her, too? You can. Want to get foals from a stallion with low fertility? You can. Want to pass down your gelding’s DNA? You can.

You can also ship your mare’s eggs and get her fertilized embryos sent back to you. You can even store embryos for as long as you want and just pull them out of frozen storage whenever you’re ready to make a new foal.

This isn’t the future; this is the here and now of horse breeding. More than ever, owners have an amazing array of options that allow for both flexibility and breeding success. In this article we’ll take a closer look at what’s new in assisted equine reproduction and what that means for horses and humans.

Intracytoplasmic Sperm Injection (ICSI)

Intracytoplasmic sperm injection (ICSI) involves injecting a single sperm into an egg, or oocyte, to provoke fertilization, producing an embryo that can then be transplanted into a recipient mare.

Physicians also use ICSI in human reproduction, but technique is especially critical for equine reproduction because standard in-vitro fertilization (IVF) has always been a challenge in horses, says Stuart Meyers, DVM, PhD, professor emeritus of anatomy, physiology, and cell biology at the University of California, Davis, School of Veterinary Medicine.

With ICSI a single ejaculate can produce hundreds of foals, says Andres Gambini, DVM, PhD, senior lecturer in the School of Agriculture and Food Sustainability at The University of Queensland, in Gatton, Australia.

Even stallions with poor semen quality can reproduce via ICSI because a single sperm is sufficient, says Edward Squires, MS, PhD, Dipl. ACT, an independent consultant at Reproductive Management, in Fort Collins, Colorado.

Because practitioners need specialized equipment and “very high-tech labor” to perform ICSI, only about a dozen equine ICSI labs operate worldwide, says Meyers.

That number is on the rise, however, with commercial embryo production “increasing tremendously,” Gambini says. That’s because, over the past decade, more labs have acquired the equipment and skilled personnel to carry out ICSI, so it has become commercially available. The technique is now spreading to other equids as well, he adds. In 2022 his team produced the first ICSI donkey, and he hopes to move on to wild equids for conservation efforts as well.

Owners of sport horse mares might find ICSI particularly interesting, because these horses can produce elite foals and not miss a beat with their athletic careers, says Christine Aurich, DVM, PhD, head of the Graf Lehndorff Institute for Equine Science, which is in Neustadt, Germany.

Even so, ICSI relies on human selection of a single sperm, rather than letting nature choose from the billions present in a single ejaculate, Aurich says.

While scientists usually choose sperm with good motility, they’re not assessing other qualities such as genetics. “ICSI takes out a lot of important selection mechanisms, and this might—in the long term—be detrimental,” she says.

Aurich points out that although no health or welfare issues have been reported with ICSI foals, there haven’t been any controlled studies on their long-term effects. Researchers at the University of Ghent, in Belgium, are currently collecting data to fill that void.

Wary of the risks of health and welfare problems, certain breed organizations, such as the Swedish Sport Horse Registry, have forbidden ICSI. Others might follow suit, she says, or at least require clear mention of ICSI on registration papers.

“There’s a lot of concern,” says Aurich. “I would be more cautious.”

Ovum Pickup and Maturation

A decade ago technicians were waiting for mares to cycle and produce mature eggs, one or two at a time, or sometimes a few more with stimulatory drugs, Gambini says, for ICSI and other techniques. Today, with ultrasound guidance, veterinarians can simply pass a needle through the vagina to aspirate all the follicles on an ovary at a single time—whether they’re mature or not—meaning they can collect sometimes dozens of eggs all at once, any time of year.

They hope to aspirate 10 to 15 immature follicles, which can be held up to 24 hours in simple culture media, and then mature them over 28 to 30 hours in media, says Squires.

Meanwhile, more and more veterinarians are getting ovum-pickup (OPU) training and are shipping oocytes to labs sometimes thousands of miles away, making ICSI an accessible option to breeders living nowhere near such specialized facilities, says Meyers.

“OPU has added all kinds of flexibility to the breeding process,” Squires says.

Still, there haven’t been many studies investigating the welfare effects of OPU, says Aurich. Despite sedation during the procedure, mares can experience pain due to inflammation that could linger for days.

Artificial Insemination and Embryo Transfer

While ICSI and OPU have advanced assisted reproduction, artificial insemination (AI), in which technicians collect a stallion’s semen and deposit it directly into a mare’s uterus, remains the current gold standard. Some owners—especially those of sport horse mares—choose to complement AI with embryo transfer, in which embryos are flushed out of the uterus after a few days and implanted in the uterus of a recipient mare.

In recent studies, researchers have been investigating the potential importance of seminal plasma—which technicians often remove when processing semen for cooled-storage or cryopreservation, Aurich says. Results from new studies suggest seminal plasma “prepares the mare’s genital tract for conception and pregnancy—something well-known from humans.”

Australian scientists have also found that hotter outdoor temperatures increase chances that recipient mares will lose the embryo. A Swiss team, meanwhile, discovered that recipient mares older than 12 have a lower pregnancy rate, and that treating recipients with antispasmodics, antimicrobials, and anti-inflammatories during embryo transfer increased pregnancy rates.

“There are certainly a few things we could still improve with AI, but when it’s done properly, it’s working very well in horses,” Aurich says.

In-Vitro Fertilization

Perhaps the biggest news in assisted equine reproduction is that scientists have finally “cracked the code” to make standard IVF possible, our sources say.

Katrin Hinrichs, DVM, PhD, Dipl. ACT, and her colleagues at the University of Pennsylvania’s New Bolton Center, in Kennett Square, realized that sperm from stallions, compared to other species, need just a little longer to mature before fertilizing an egg. So, they developed a culture system that keeps stallion sperm alive for 25 hours in a dish—allowing them to reach the maturity level needed for successful fertilization.

With a 90% fertilization rate, the discovery offers a far simpler and less expensive method of producing embryos than ICSI does—while still allowing the natural sperm selection process by exposing each egg to thousands of sperm, Aurich says.

Because labs can carry out traditional IVF more easily than they can ICSI, Meyers says the technique will likely start taking off in the horse industry.

Cloning

Cloning technology continues to expand on a commercial level, Gambini says. It’s most popular in the Americas—and especially in Argentina, where three cloning companies produce about 200 foals a year.

Cloning allows owners to get essentially exact replicas of their current horses because they want the same qualities or plan to breed the clone of a sterilized horse. Even so, research findings suggest that the “empty” egg used to create the embryo, the uterine environment, and life experience shape the animal as well—what scientists call “epigenetics,” he explains.

Researchers conducting recent equine cloning studies have focused on improving the selection and maturation process of recipient eggs. Scientists also discovered the possibility of changing clones’ sex when they realized that a foal cloned from a male horse had a missing Y chromosome.

However, some breed associations refuse to register clones, which hampers the technique’s uptake in the industry, Squires says.

Blastocyst Time-Lapse Monitoring

Time-lapse videos of microscopic images of growing embryos have recently given critical insight into how and when the first cells split—or cleave—during the early blastocyst stage.

“There’s a video screen on the incubator, so you can always go look at how the embryos are developing without opening the incubator,” says Meyers, whose team developed the technique.

That’s important, they found, because early cleavage time relates to pregnancy success. Comparing time lapses of blastocysts that did or did not later become foals, Meyers and his colleagues found the most successful embryos had first cleaved within 28 to 30 hours after ICSI. Those cleaving before or after that range were less successful.

Time lapse is critical to actually watch the embryo grow, Meyers says.

Conservation and Shipping

Storing and transporting sperm, eggs, and embryos provides great flexibility for breeders as they select long-distance breeding partners, wait for optimal ovarian cycling stages, choose ideal foaling times, and plan for future foals, our sources say.

Thus, conservation and shipping have been hot research topics. Australian scientists recently discovered, for example, that stallion sperm—unlike those of other species—can stay active as long as their mitochondria maintain their metabolism. Five years ago, the research team developed a special extender that supports the mitochondria’s metabolism. The result was semen that remains alive and fertile at room temperature for up to two weeks—allowing for long-distance shipping without the fertility loss associated with freezing and thawing, Aurich says.

Eggs survive relatively well for 24 hours when stored in passive coolers that bring them slowly from body temperature to room temperature, Meyers says. But better yet are new battery-operated, temperature-
controlled boxes—especially when ambient temperatures get extreme.

As for embryos, an “ultra-rapid freezing” process called vitrification keeps embryos healthy during storage in liquid nitrogen, Squires says. After thawing, he notes, the embryos are practically as viable as they’d been prior to vitrification. 

The key, he says, is vitrifying them before they reach 300 microns in width—easy to do for lab-grown ICSI and IVF embryos.

Gambini and his team are currently applying ICSI and vitrification to conservation programs for rare donkey species. “You can have that embryo frozen pretty much forever,” he says.

Unfortunately, however, vitrification is less feasible for preserving embryos made in utero because they can’t be measured as closely and are usually bigger than 300 microns by the time they can be flushed, Squires says.

Genomics, Genetics, and Sexing

Worldwide, genome research is on the rise, paralleling an increase in equine gene studies. Multiple research groups are presenting early phases of their work at scientific meetings such as the biennial Havemeyer Equine Genome Workshop.

While an initial practical aspect—which is already in use—involves genetic testing for monogenetic diseases such as severe combined immunodeficiency in Arabians, fragile foal syndrome in Warmbloods and Thoroughbreds, and hereditary equine regional dermal asthenia in Quarter Horses, scientists are also looking into how genes affect fertility. For example, researchers have recently discovered that contrary to previous belief, sperm produce messenger RNA, which could offer biomarkers for fertility, Aurich says.

Gene editing—manipulating genes in order to get the exact ones breeders want—and gene therapy—correcting mutations to prevent their related diseases—is now possible in research settings, Squires says. However, we could be several years away from having these options in a commercial setting, especially gene editing, which raises ethical concerns. “Not everybody agrees with how much technology we should be using,” he says. “And maybe it’s a slippery slope; I don’t know.”

Scientists also now have the capacity to sex embryos and sperm, Squires adds. “It’s being done,” he says. “And it’s probably going to be done more and more.”

Regardless, people should be wary of existing commercial products offering genetic advantages or sexing, such as semen extenders that claim to let breeders select for male or female, says Aurich. “There’s no scientific evidence that this will work, but people are buying it,” she says. 

Horse Welfare

More and more, scientists realize that assisted reproduction offers horses better welfare than live cover does, our sources say.

In-hand breeding often forces mares to receive stallions they would not have accepted if given the choice, Aurich says. Horses can be aggressive toward each other and even cause serious injury—both on pasture and out in the wild. Artificial breeding might be somewhat invasive, but it’s generally better physically and mentally for mares.

And if they’re undergoing OPU, they can give so many eggs at a time that they might only have one procedure a year, Gambini says. Stallions, meanwhile, can produce so many foals with a single ejaculate that they can spend less time in the breeding shed covering mares—a process that is not only exhausting but also potentially stressful and even dangerous with unwilling mares.

Nonetheless, breeders still must ensure stallions have opportunities to express natural behaviors, such as having social contact with other horses and being near a friendly mare in heat when having semen collected, Aurich adds.

“I am convinced that assisted reproductive technologies contribute to animal welfare in horse breeding, if driven by expertise and reason,” she says.

Nonetheless, horses must never be exploited, Aurich adds. “Not every retired sport horse mare must become pregnant,” she says. “They may prefer a lovely retirement on pasture instead.”

Take-Home Message

In recent years scientists have made significant headway improving assisted reproduction techniques in horses, especially regarding ICSI, OPU, IVF, and semen, egg, and embryo storage. These advances lead to better success rates, more breeding options and flexibility for owners, and reduced costs, while also offering the possibility of improved welfare for the horses involved.

This article is from the Research Roundup 2024 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.

Do’s and don’ts to meet the dietary needs of retirees and pasture pets

For creatures of any species, proper diet and exercise are key to maintaining health and proper body weight and condition. But when a horse isn’t getting regular exercise, the onus falls on diet alone. And, of course, this presents its own set of challenges.

A horse might be idle for a variety of reasons. He could be a senior mount who has served his time in work and is enjoying a well-deserved retirement. She could be a young prospect who is getting time to grow and mature before starting in training. Or he could be a mature campaigner with a performance-limiting injury who’s embarked on a new career as an equine babysitter.

No matter the reason for horses’ inactivity, and even if they’re not being managed as intensively as is typical, owners must remain attentive to these animals’ diets. In this article you’ll learn some do’s and don’ts for promoting nonworking horses’ optimal health (and preventing potential problems) with nutrition.

Defining “Nonworking”

“When a horse is not working, we often refer to them as being ‘idle’ and, more than likely, we are talking about a horse that is either retired or is idle due to disease, injury, weather/season or time of year, or perhaps in between competitions or events,” says Amanda Adams, PhD, MARS EQUESTRIAN Research Fellow at the University of Kentucky M.H. Gluck Equine Research Center, in Lexington. “Or in my case they are simply part of the family and, if we are both lucky, we trail/pleasure ride a few times a year, time permitting and, thus, there is quite a bit of ‘idle’ time.”

As it turns out, idle horses make up a large portion of the equine population in the United States. “The latest reportings from American Horse Publications, in 2018, listed the top two ‘use of horse’ categories were for trail/pleasure riding and idle/retired/not working,” she says. 

Don’t: Ignore Body Condition

While your nonworking horse doesn’t necessarily need to carry a rider around a jump course or up and down a trail, his fat cover remains an important part of his overall health, says Krishona Martinson, PhD, professor and equine extension specialist at the University of Minnesota College of Food, Agricultural and Natural Resources Sciences’ Department of Animal Science, in St. Paul.

“We know that both thin and obese horses are at a greater risk for certain disorders compared to horses at a healthy or recommended body weight,” she says. “For example, horses that become overweight have a higher chance of suffering from laminitis and tend to have challenges controlling their body temperatures (e.g., can overheat).”

Conversely, underweight horses could lack the fat stores necessary to withstand low temperatures and other stressful situations. They can develop health issues such as weakness and impaired gastrointestinal function, wound healing, and immunity.

Do: Evaluate Weight and BCS Regularly

Nutritionists and veterinarians recommend keeping horses around a body condition score (BCS) of 4 to 6 on the 9-point Henneke scale. The trick to maintaining a healthy weight and BCS? Monitoring them regularly so changes don’t sneak up on you.

“We recommend that owners track their horse’s body weight and body condition score on a monthly basis,” Martinson says. “It takes a minimal amount of time and can easily be done while grooming.”

A scale is the most accurate way to evaluate body weight; however, few owners have frequent access to a scale. Instead, they can estimate body weight using a weight tape or formulas such as those offered on TheHorse.com (­TheHorse.com/weightcalculator) or the Healthy Horse smartphone app, which Martinson helped develop at the University of Minnesota.

“Research has found that the Healthy Horse app results in a more accurate estimation of body weight compared to the equations and a weight tape,” she says. “Similar to mathematical equations, the app requires owners to take four ­measurements—height, neck circumference, body length, and girth ­circumference—and, once entered, the app estimates body weight.”

Likewise, owners should evaluate a horse’s BCS to identify changes, subtle or pronounced. Find a step-by-step guide on determining BCS at TheHorse.com/164978.

Also consider a horse’s cresty neck score, or CNS, Adams says. “The CNS evaluates the amount of fat in the neck region of the horse using a scale from 0 (no visible crest) to 5 (large crest that falls to one side),” she says. “The ideal CNS is 2 or lower; a score of 3 or greater has been recently shown to be a predictor of insulin dysregulation.”

Do: Consider the Horse’s Life Stage

Whether young and unbroke, mature and injured, or old and retired, your idle horse has specific nutrient needs based on life stage. For example, Martinson says, young horses have unique and important nutrient requirements to ensure safe and consistent growth and skeletal development and to put them on the right path for good health over their entire lives.

Pregnant and lactating mares require enough calories and nutrients for themselves plus their developing dependents.

Then there are our senior equine friends that face a number of possible health issues that impact body condition and nutrient requirements, from dental issues to diminished digestive efficiency. They might require a higher-fat diet than a normal adult horse to help maintain weight, or they might not be able to chew hay or grass well enough for their bodies to extract the nutrients they need.

Adams, who’s studied older horses extensively, cautions that it’s important to consider the aging horse’s metabolic status to pinpoint or rule out underlying issues that could impact his or her ideal diet, such as equine metabolic syndrome, insulin dysregulation, or pituitary pars intermedia dysfunction (equine Cushing’s).

“Metabolic status will definitely drive how the horse is managed and what diet they should be maintained on,” she says.

Don’t: Overlook Nutritional Needs

Idle horses or horses at maintenance have similar vitamin, mineral, protein, and other requirements as working horses, even though they’re not working.

“It’s best to reach out to an equine nutritionist, local extension educator, or veterinarian to help you determine what type of diet your horse should be maintained on,” Adams says, but notes key points to remember about any horse’s diet:

• Forage (grass and/or hay) should be the foundation. “A horse typically requires 1.5-2.5% of their body weight in forage daily, and this varies depending on their BCS, age, and working status,” she says.
• Having hay analyzed is key to ensuring a horse’s nutritional needs are being met. You can work with an extension agent to help with this, or you can send a sample for analysis to a forage laboratory (such as ­EquiAnalytical).
• Importantly, provide adequate clean, fresh water, because an average size horse will drink 5-10 gallons per day.

If horses are at a healthy body weight and have access to good-quality hay, then a ration balancer is usually the only additional feedstuff needed, Martinson says (more on these in a moment). “And if the horses are on pasture for the majority of the time, it’s possible no additional feedstuffs are required,” she says.

Keep in mind that while good-quality pasture can supply all the nutrients some horses need, it can inevitably lead to unwanted weight gain.

“In this case, a grazing muzzle can help limit intake while keeping the horse on pasture,” Martinson says.

Of course, reducing pasture intake reduces the nutrients a horse consumes, so muzzled horses might also benefit from a ration balancer to meet their nutritional needs. Again, “working with an equine nutritionist is the best way to ensure your horse, regardless of activity level, is getting proper nutrition,” Martinson says.

Do: Consider Ration Balancers

For idle horses that need proper nutrient levels without the calories of commercial feeds, balancers are the answer.

“A ration balancer is essentially a supplement because it is not a complete feed or a performance feed,” Adams says. “It does not provide calories, as it is designed to only provide (high-quality) protein, vitamins, and minerals that may be lacking in a horse’s diet. A ration balancer is a heavily fortified formulation that is fed in small amounts of 1 to 2 pounds per day per horse that (balances the diet) without causing the horse to pack on additional pounds.”

Another reason they’re helpful for idle horses is, because of their low-calorie status, they’re low in starch and sugar, or nonstructural carbohydrates (NSC). For this reason, says Adams, they have a low glycemic index that’s ideal for horses with metabolic issues, especially those prone to laminitis.

Do: Increase Forage First for Underweight Horses

Yes, many idle horses gain weight in the absence of regular exercise. But a few will drop pounds or remain lean when they’re not in work. Owners might discover a horse doesn’t thrive in a 24/7 turnout scenario, for instance, or temperature extremes might result in weight loss. Underlying medical issues, such as poor dental health or undiagnosed infections, could cause a horse to be underweight, and Martinson says it’s important to rule those out first before adjusting the diet.

“Assuming there are no underlying medical issues, it usually best to either increase the amount (or) quality of forage fed,” she says. “For example, going from a poor-quality grass hay to a better-quality grass-legume hay can sometimes be enough to result in weight gain.”

She cautioned horse owners to make any dietary changes slowly over the course of seven to 10 days.

Consistent Attention Is Key

Just because a horse isn’t actively working doesn’t mean his diet isn’t an important part of his well-being. 

“All horses, regardless of working status, have nutrient requirements that need to be met,” Martinson says. “For adult idle horses or pasture pets, keeping these horses at a healthy body weight is usually the challenge.

“Consistently tracking body weight, body condition score, and other indicators of healthy body weight are key,” she adds. “Using research-based tools is also important and include grazing muzzles while on pasture, slow-feed haynets, and ration balancers. Finally, these horses rarely require grain, and owners should focus on maximizing forage in the diet.” 

Adams recommends turning to the experts if you are unsure of how to monitor your horse’s condition or design his diet. “That’s their job, let them help guide you,” she says. “Don’t guess, ask, because guessing can lead you and your horse down the wrong path.”

One of the most important complications in neonatal foals is failure of passive transfer (FPT). This is the inadequate absorption of antibodies from the mare’s colostrum. Approximately 5-20% of newborn foals are diagnosed with FPT. They are at risk for developing serious medical conditions.

To learn why passive transfer is so critical, how to check antibody levels in your foal, and what to do if failure of passive transfer occurs, follow the steps illustrated in this infographic.

This infographic gives you a visual understanding of how your newborn’s immune system functions. Then you can work with your veterinarian to prepare for foaling. And once the foal is born, you can ensure he receives the protection he needs.

Q: My new mare’s previous owners said she’s a hard keeper during the winter and recommended adding fat to her diet in the colder months to help maintain her weight. But when I looked online, I found many recommendations about different supplements, oils, and grains, and I’m not sure where to start. What’s the best way to add fat to a horse’s diet, and which products are most effective?

A: When adding fat to the diet for weight gain it is important to ensure the diet remains well-balanced. Therefore, the most nutritionally complete way to add a fat source to your horse’s diet is to use a higher fat fortified commercial feed fed at the recommended daily intake level. These feeds often having 10-12% crude fat, not only adding fat to the diet but also essential vitamins and minerals, protein, and other nutrients.

Oils are a great way to add fat calories to a ration but provide only calories, not other nutrients. Depending on the rest of the horse’s diet, it is possible when supplementing oil to provide your horse with adequate calories but create a diet that is deficient in other key nutrients, especially minerals and vitamins. This could hinder weight gain, as these essential nutrients are necessary for proper functioning of metabolic pathways. Another benefit of using fortified high-fat feeds is that they tend to contain sources of highly digestible fiber, such as beet pulp and almond hulls, so you have the benefit of adding cool calories from two different sources: fat and fiber.

Rice bran is a popular choice due to a fat content of more than 20% on a dry matter basis. Rice bran should be stabilized and typically has added calcium carbonate to balance its otherwise high phosphorus content. However, few rice brans are otherwise fortified, so are unlikely to help with the overall provision of other necessary essential nutrients. Some better-quality rice-bran products will have added vitamin E. This in part helps maintain the product’s shelf life; horses with higher fat intakes also have higher vitamin E requirements. For this reason, if you compare feeds that have, say, 6% versus 12% crude fat, you will typically find that the 12% crude fat feed has a higher vitamin E content.

It is tempting and easy to pour oil over an existing diet, which will certainly increase calorie intake; however, feeding large amounts of oil can backfire. If you overwhelm the small intestine’s ability to digest and absorb fat it will pass into the cecum and large colon where it can disrupt fiber fermentation. This could actually result in weight loss as the horse would not be able to get as much nutritional benefit from the forage in the diet. With very high intakes or sudden introductions of larger amounts of oil, manure can become oily. For these reasons, introduce oil slowly over 10 to 14 days, increasing by no more than a quarter cup every two to three days until you reach the desired amount.

Oils all have different compositions of fatty acids, and recently omega-3 versus omega-6 fatty acids have gained a lot of attention. This is because these fatty acids play important roles in cell membrane fluidity, inflammation, and immunity. Both are necessary for these important functions, but relative amounts of each might influence overall response. As a result, corn oil is no longer as desirable as those oils with higher omega-3 contents such as canola oil. Flax oil and camelina oil provide more omega-3 than 6 fatty acids and are good choices; however, in large amounts cost might be inhibitive.

An 8 fluid ounce measuring cup holds approximately 200 g of vegetable oil, which provides 1.8 Mcal of digestible energy, which is about 10% of a 500 kg (1,100 pound) horse’s maintenance requirements and is comparable to the energy provided by just over a pound of oats. Even though the horse’s natural diet is relatively low in crude fat, horses appear to utilize fat well and have been fed up to 230 g of fat per kilogram dry matter consumed as corn oil. However, the National Research Council cautions against feeding soybean oil at intakes exceeding 0.7 grams per kilogram body weight per day. Therefore, it is likely best to keep supplemental oil intake at no more than about 2 cups per day for an average sized horse.

Lastly, consider whether increasing fat is actually the best feeding option for preventing weight loss in winter. Many horses lose weight in the winter due to the additional calorie expenditure used to keep warm. Feeding extra hay not only increases calorie intake but also generates internal heat due to the fermentation process necessary for digestion in the horse’s hind gut. Therefore, increasing forage for horses that have good dentition is always my first choice.

Q. My long yearling Dutch Warmblood mare knocked her tooth out so severely that it had to be removed by my vet. We’re not sure how she did it but I thought that, since it’s a baby tooth, it would be fine (like the kindergartner who knocks out a front tooth and just needs to wait for the adult tooth to grow in). However, I’m coming to understand that it might be different for horses. What is the long-term prognosis for a young horse losing a tooth prematurely?

—Laura, Seattle, Washington

A. The traumatic, premature loss of a deciduous incisor (or “baby tooth” as you’ve referred to it) can be problematic in any species and, in fact, may be urgent in horses. Missing teeth in horses generally lead to malocclusions (misaligned bite) or pathologic (disease-causing), dental problems.  The ability of the horse to effectively use their mouth for eating may be negatively affected by the loss of any one or more teeth. Fracture of the bone that contains the incisors in either the upper or lower jaw is the most common fracture of the horse’s skull, and I see it mostly in “mouthy” colts and less often in fillies.

In the case of your filly, the deciduous central incisor tooth in the lower jaw probably dislocated from the surrounding alveolar bone, or tooth socket, when your filly put her teeth on a hard object and pulled back, or she may have gotten kicked during play. The bony tooth socket most likely broke outward, toward the lip. In a long yearling, the root of the baby tooth is strong because it’s not due to shed until the permanent central incisor erupts at 2 1/2 years.  Prior to eruption of the permanent tooth the root of the baby tooth will become very thin.  In either case, a force strong enough to break the bone may also break the tooth root.  Your veterinarian chose to extract the tooth so the root may have also been fractured.  What remains to be seen is whether the developing permanent tooth bud, which is near the baby tooth, was also damaged. Hopefully it was not, and the tooth will develop and erupt normally. At the very least, I would expect the permanent tooth to erupt a bit prematurely with respect to the adjacent permanent incisor due to the lack of the baby tooth above it.

Crowding may occur should the baby teeth on either side of the missing tooth drift toward the midline. This crowding frequently causes the permanent tooth to make its way towards the surface in a displaced position, usually towards the tongue.  In this case, your veterinarian can perform careful odontoplasty to remove any dental tissue impeding the permanent incisor’s eruption. The occluding tooth in the upper jaw will also require attention, as it will erupt unimpeded downward into the void of the missing baby tooth.

Your veterinarian may want to take periodic radiographs to assess the developing permanent tooth prior to its scheduled eruption. If the tooth bud was damaged, the developing permanent tooth will either never develop or develop in a misshapen way which can cause eruption or periodontal problems. It may even form a cyst within the bone that may expand and damage adjacent teeth. The radiographs above demonstrate the problematic, incomplete, misshapen development of a tooth in a case of a fractured incisive bone. The following pictures are of a two and a half year old mustang with a kick injury to his upper and lower incisors.

Serial radiography will help your veterinarian decide how to best use interventional dental procedures to help your filly attain the most normal, functioning dentition possible.  In any case, the mouth will find a way to function but your veterinarian can help your horse to achieve an optimally functioning mouth.

If your horse’s gut microbiota is out of whack, microorganism-packed products might get him back on track

Inside the digestive system live millions of microscopic organisms that play vital roles in the horse’s digestive—and general—health. Many of these of bacteria, protozoa, archaea, and fungi help break down food and usher nutrients efficiently into the bloodstream. They play a role in metabolizing fiber, generating energy, and promoting proper intestinal transit.

While scientists still don’t know what makes up the ideal equine gut microbiota, they do know it’s a question of balance. “All these microorganisms live in a kind of symbiotic relationship when they’re in balance,” says Kathleen Crandell, PhD, a nutritionist with Kentucky Equine Research, in Versailles.

Without listing the thousands of species or labeling certain microbes as good or bad, let’s briefly say the “right” balance includes more Lachnospiraceae and Ruminococcaceae bacteria, which break down plant materials, and fewer Streptococcus and Lactobacillus bacteria, which produce lactic acid, Crandell says.

When that balance gets disrupted, so too does the symbiotic relationship, she explains. Horses might have intestinal discomfort, develop diarrhea, lose weight, experience energy loss and poor performance, seem generally unwell, and become more susceptible to illnesses.

To help shift that balance back in a direction that favors good health, scientists have isolated certain species of microorganisms from the microbiome and packaged them into oral powders, pastes, and liquids. These are probiotics.

You often see probiotics and prebiotics (fiber sources for the microbiota to break down, or “food” for the probiotics) packaged and supplemented together, but for the purpose of this article, we’ll focus on the former.

Assessing Safety and Efficacy

Study results show probiotics are safe for most horses, Crandell says. But while in theory they should work, little hard scientific evidence shows they are beneficial.

Most of the important digestive action in horses occurs in the cecum and colon—the hindgut—where fiber, in particular, the mainstay of equine nutrition, gets broken down, says Simon Daniels, PhD, senior lecturer of equine management and science at the U.K.’s Royal Agricultural University, in Cirencester. It’s here probiotics need to work their magic most, ideally reversing upsets in the favorable ratios between microorganism species.

The only way to get probiotics to the cecum, though, is orally—meaning the microorganisms must endure the acidity and digestive processes of the stomach and small intestine first. “We don’t really know how well they survive that journey, but we do know (these conditions) have an effect on it,” Daniels says.

Researchers also aren’t sure if the probiotics stay in the cecum or keep moving out the other end, but initial study results suggest they don’t stick around, says Crandell. “They don’t seem to colonize,” she says. “So the effect might only last as long as the probiotics are being given.”

While scientists haven’t confirmed probiotics’ effects in horses, they seem safe to try in most cases, she says. “For the moment, it’s really one of those things where it can’t hurt and might help.”

Top 5 Horses That Need Probiotics

It doesn’t matter whether your horse is an athlete, a broodmare, a senior, or a pasture pet, our sources say. What matters is if he falls into a category of likely having gastrointestinal (GI) microbiota imbalance. Here’s a list of the Top 5 types of horses that might make good candidates for probiotic therapy.

The horse with diarrhea

Defecation that’s too frequent and usually soft or even liquid is often a telltale sign of gut microbiota upset. “If there are problems in the microbiome, then the fecal consistency becomes soft,” says Daniels.

While it’s important to pinpoint the underlying condition to treat medically, owners can start probiotics to address digestive upset right away. “Using probiotics would be a way to try to stabilize that gut ecosystem in a horse with diarrhea or just loose droppings, even for unexplained reasons,” Daniels says.

Crandell agrees: “For an adult horse with diarrhea, probiotics would definitely be one of my go-tos.”

The “leaky gut” horse

Horses—like humans—can experience alterations in intestinal permeability that are commonly referred to as leaky gut. A layer of microbiota lining the inside walls of the digestive tract helps digest nutrients while also working as a barrier, keeping pathogens (disease-causing organisms) and large, undigested molecules from passing through the usually tight cellular junctions of the intestinal walls and slipping into the bloodstream, explains Crandell. “The gut really is leaking,” she says. The body’s response to circulating pathogens is inflammation, leading to generally compromised health. Horses with leaky gut can have diarrhea and show signs of intestinal discomfort such as mild colic.

“The idea is to give a probiotic that has the beneficial microorganisms necessary to reinforce the barrier and keep that gut from becoming leaky,” says Crandell.

In theory, she says, it should work— and studies in humans and rats using live yeast and Lactobacillus and Bifidobacterium bacteria suggest it might, she says.

The stressed horse

Probiotics can’t do anything about stress itself, but our sources say these products can help with its side effects.

Stressed horses release large amounts of cortisol—the “stress hormone”—into their bodies, usually altering gut motility (which is why stressed horses have more frequent, liquid feces). When stress is short-lived, the gut can usually restore order itself. But when stress is prolonged or intense, the horse might struggle to get the microbiota back in balance.

Daniels typically sees probiotics as more of a fix than a preventive approach, but there’s no harm in giving them to horses before stressful times. “If you have a particularly high-strung animal that’s going to be traveling, for example, you could give probiotics in advance,” he says. “Hopefully that will help stabilize any effects in the gut.”

Crandell recommends starting probiotics a week before a stressful event. But horses used to travel and other high-stress situations probably don’t need them. “If it’s a seasoned show horse going off to events like any other day in his life, that’s not the kind of horse that might benefit,” she says.

The horse with high energy needs

Sport horses, certain broodmares and older horses, and hard keepers have higher energy needs and usually require a special diet. Often that means providing high-starch concentrated feeds. Large quantities of starch, however, can make the digestive tract more acidic, says Crandell. Worse, any starch that doesn’t get digested in the small intestine can make it back to the cecum.

“It starts to get broken down by starchloving bacteria there, and they produce lactic acid, which causes the pH to drop,” she says. In this acidic environment, the balance shifts, and the wrong microbes become dominant. “So what you’re doing by feeding a probiotic is trying to stabilize that pH in the hindgut.”

Meanwhile, probiotics could also help the GI tract extract energy from fiber more efficiently, says Daniels. “Researchers in animal nutrition and gut health have been working for a long time to try to improve the use of fiber,” he says. Haylage, for example, has higher energy content than hay and could replace some or all of a horse’s starchy feed ration. But for horses to benefit from the energy in haylage, their bodies must be able to extract it out of the fiber. Also, “obviously, when there’s high fiber in the diet, it’s got to be highly digestible,” he says.

Probiotics can provide the microbes necessary for breaking down fiber, Daniels says. “Especially for sport horses, you really want to make sure you’re getting the maximum amount of what you put in.”

Because of these potential benefits, manufacturers often add probiotics right into packaged feed, he says. “If you can potentially improve fiber degradability or reduce the harmful effects of starch, then that’s not a bad thing.”

The medicated horse

Despite their good, drugs can come at a price. Antibiotics, in particular, but also steroids and non-steroidal anti-inflammatories, can upset the gut microbiota balance as the drugs incidentally attack favorable bacteria or change the acidity of the environment. Even dewormers can change microbiota, and not all horses can get the balance back on their own, says Daniels.

Horse owners don’t necessarily need to give probiotics before or with the drug, he says—or at all. But they can monitor medicated horses for signs of gut trouble, which usually shows up as diarrhea.

“The classic example would be the horse that gets an injury and gets antibiotics, and now the droppings are loose,” Daniels says. “So then you want to restabilize things and get them kick-started again, so you add some probiotics.”

Special Concern: Young Foals

A new foal develops his unique gut microbiota rapidly, picking up microbes from the dam’s teats and skin, her droppings, and surrounding surfaces. So early life might be the wrong period for supplementing, says Crandell.

Daniels agrees: “From the studies that have been undertaken, it appears there is limited benefit in very young foals that are developing their own microbiome, which is initially heavily influenced by their dam and the milk diet.”

Research findings hint at a vulnerable period between 7 and 28 days of age when caretakers might want to avoid giving probiotics, Crandell says.

Existing Probiotics Research

Whereas probiotic research in humans is vast, very little research has shown the effect of probiotics in living horses.

A few teams around the world are trying to fill that gap. At Colorado State University, researchers have looked at how probiotics might help horses clear sand from their intestines (although the results weren’t very optimistic). Meanwhile, a U.K. group has studied the effects of yeast supplementation on ponies’ fecal microbiomes, with more positive results. Slovakian scientists have isolated bacterial strains from horse feces to test their effect as an equine probiotic. Lithuanian researchers are assessing the effects of newly isolated Lactobacillus species on endurance horses. And Dutch researchers are investigating how topical probiotics might help limb wounds heal.

On the other hand, scientists (Berreta et al., 2020) found inconsistencies between product labels and ingredients as well as the presence of antimicrobial-resistant genes in the bacteria of some commercial veterinary probiotics.

Daniels says he’s hopeful that scientists will investigate the link between the microbiota and horse behavior and how probiotics might influence it. “I think we are all realizing that we are what we eat and that diet has a strong influence on not just our gut health but our overall health, moods, and behavior,” he says. “I think it’s extremely likely that the same happens with the horse.”

Take-Home Message

By supplementing horses with the same kind of beneficial microorganisms that colonize their guts, probiotics might help reestablish healthy balances in the gut microbiome without causing harm. While research is still inconclusive about their efficacy, our sources believe these products might be worth trying when horses show signs of intestinal upset caused by illness, medications, stress, or feed or to get the most out of fiber’s energy supply.

What equine researchers continue to learn about this perplexing and frustrating stereotypy in horses

Hup. Huupp. <Pause> Huuuppp. If you’re hearing noises in your barn that sound like they’re coming from a pig/toad hybrid, you’ve probably got a cribber. Cribbing horses bite onto a hard surface, such as wood, then pull back to suck in air across their oropharynx, creating that characteristic raspy, croaking noise.

Cribbing—also known as crib-biting—is a somewhat rhythmic, repetitive behavior that seems to have no purpose. Therefore, it fits the definition of stereotypy. And while cribbing might seem pointless, that doesn’t mean it causes no harm. Long-term, it’s associated with abnormal dental wear and possibly poor body condition, poor performance, and gastrointestinal disorders—as well as damage to barn structures.

Scientists have been talking about cribbing for the past 400 years, says Sebastian McBride, PhD, senior lecturer in biological science at Aberystwyth University, in England. And they’ve been homing in on domesticated equine life as its primary culprit since the 1800s—without fully understanding why domesticated life would cause the condition.

Since then, scientists have been getting to the root of equine cribbing as they explore brain anatomy, genetics, potential causes, health consequences, welfare, treatment, and more. With each decade they’re learning more about the whens, whys, and hows of this and other stereotypies in horses, humans, and other animals. Here’s what we’ve learned about cribbing since we published our last research update eight years ago.

1. Cribbing is a stress-coping mechanism, not a ‘vice.’

More than any other factor, it seems horses develop cribbing and other stereotypies when they experience intense and/or prolonged stress, says Jéssica Carvalho Seabra, PhD, of the Federal University of Paraná, in Curitiba, Brazil, and Colorado State University, in Fort Collins. In 2021 Seabra completed a systematic review of recent scientific studies on factors affecting the development of abnormal behaviors, involving 18,863 equids.

Her investigations revealed people don’t always realize it’s the stress of domestic life that’s provoking stereotypies. A luxurious barn can still be a place of solitary confinement for a roaming, herd-living animal. And weaning at six months—while traditional—is a highly stressful event for a species in which nursing naturally lasts much longer.

“This is a problem because people from the equine industry like traditions,” says Seabra. “They like to keep raising horses the same way their ancestors used to do. So you can go to a very fancy equestrian facility, and you think, ‘They’ve got all this nice stuff, but they don’t have the basics.’ ”

On the other side of the globe, Swiss researchers and sisters Elodie Briefer, PhD, and Sabrina Briefer Freymond, PhD, have been investigating cribbing for more than a decade. Among their discoveries about the condition, they’ve found cribbing horses have lower cortisol (stress hormone) levels than noncribbers when learning complex tasks, provided they’re allowed to crib during the training session. This confirms cribbing might be a stress-coping ­mechanism.

Importantly, cribbing, like other stereotypies, shouldn’t be called a vice, our sources say, because it is, in fact, a seemingly purposeless behavior—the horse isn’t being naughty. Rather, cribbing horses have found a way to cope with the stress they’ve endured or are enduring.

“People seem to feel that cribbing is somehow morally wrong,” says Katherine Houpt, VMD, PhD, Dipl. ACVB, professor emeritus at Cornell University’s College of Veterinary Medicine, in Ithaca, New York. “But even if animals could do something that’s morally wrong, cribbing isn’t it.”

2. Cribbing literally changes the horse’s brain.

Stereotypies such as cribbing are associated with the dysfunction of dopamine, a neurotransmitter involved in learning. Surges of dopamine in the striatum, part of the brain’s basal ganglia, reinforce learning and habit formation. But stress can interfere with dopamine release, especially in “hypermotivated” individuals, McBride says. It can create permanent physical changes in the striatum.

These permanent brain changes might explain why cribbing horses—as well as other individuals with such complex motor stereotypies—rarely stop performing their stereotypies once they’ve started, Seabra says. “Once it’s damaged, there’s no way to go back to what was before.”

In recent years researchers have also investigated the brains of humans and mice with stereotypies—especially because 44% of people with autism experience stereotypies such as hand-flapping or -rotating. Studies have pointed to two additional chemicals in the brain—gamma-aminobutyric acid (GABA) and acetylcholine—involved in stereotypy development, says Thomas Fernandez, MD, who studies neuropsychiatric disorders at Yale University School of Medicine, in New Haven, Connecticut.

The brain might also be affected by ghrelin, a peptide produced in the stomach that can enter the brain through the circulatory system, explains Carissa Wickens, PhD, an associate professor and extension equine specialist at the University of Florida, in Gainesville. Citing a 2017 review focused on humans and rodents, she explains that ghrelin—levels of which are higher in cribbing horses than noncribbers—is part of the gut-brain axis (more on this in a moment) and regulates hunger, gut motility, stress, anxiety, and fearlike behaviors.

In the U.K., scientists found cribbing horses blink less often and change up their activities more often than noncribbers. The findings provide additional evidence that cribbers’ striatums work differently from those of noncribbers, the researchers say.

3. It has a genetic component.

Scientists have long suspected cribbing is partially hereditary, because it’s more common in Thoroughbreds and Warmbloods and even in certain family lines, says Wickens.

Researchers conducting early genomic analyses in 2014 came up empty-handed, however, finding no links between cribbing and eight suspected genes. Since then, no studies have been published on the topic—but that doesn’t mean the “cribbing gene” doesn’t exist, she explains. Scientists have yet to investigate other important candidate genes, such as those controlling certain dopamine and GABA receptors. 

For Houpt, it’s a critical mystery to resolve. “I’m sure it’s genetic,” she says. “We just haven’t found what it is yet.”

Convinced, Seabra even suggests people stop breeding cribbing horses. “There is a possibility of passing that genetic predisposition on to the offspring,” she says.

4. Cribbing has gut microbiome and antioxidant components.

Over the past eight years scientists across the globe have been making connections between the gut microbiome (the ecosystem of microbes living there) and mental health. Their findings have strongly supported the existence of a “microbiota-gut-brain axis”—meaning the brain and the gastrointestinal tract are strongly linked.

Wickens and her team investigated the gastrointestinal microbiome in four cribbing versus four noncribbing horses. They found the cribbers had a higher abundance of pathogenic bacteria in their feces—­suggesting a higher abundance in the hindgut, as well. That might be due to stress, which provokes the adrenal gland to release norepinephrine and epinephrine into the blood, which quickly reaches the gastrointestinal tract. There, the presence of these neurotransmitters could interfere with a healthier microbiome balance, she says.

Meanwhile, Iranian researchers found blood antioxidant levels were lower in cribbing than in noncribbing horses, suggesting oxidative stress might play a role in the pathology. The team recommends further study, which could eventually lead to the identification of biomarkers and effective treatments for cribbing, they say.

5. It might not be directly related to stomach acid (and, hence, gastric ulcers).

Twenty years ago scientists were hot on the trail of connecting stomach acid and gastric ulcers to cribbing. Data suggested pH was more acidic in the stomachs of crib-biting horses, and researchers suspected cribbing increased saliva production, acting as a self-medicating buffer—yet not enough to keep the pH as low as that of noncribbers. 

Even so, researchers agree that “the mechanism is unclear.” That’s in part because in 2012, Houpt confirmed cribbers don’t salivate more than noncribbers. And in 2013 Wickens found that equine gastric ulcer syndrome (EGUS) wasn’t more prevalent in cribbers, even if cribbers had a higher serum gastrin response after eating concentrated feeds—suggesting they might have altered gastrointestinal physiology, she says.

In 2019 Simon Daniels, PhD, of the Royal Agricultural University, in Cirencester, U.K., compared cadaver stomachs of cribbers and noncribbers and found no anatomical or physiological differences. His team concluded that cribbing and EGUS might not have a direct link after all. Rather, both conditions might result from the same source: stress.

6. Cribbing might be related to other health risks, including colic.

Cribbing horses generally wear their incisors down gradually, which can interfere with dental health and proper forage consumption, our sources say. And some scientists have identified cribbing as a risk factor for osteoarthritis in the temporohyoid, a joint in the head behind the throat.

In general, researchers agree cribbing horses tend to colic more, and they have identified two types of colic in particular: epiploic foramen entrapment and colonic obstruction distension. However, scientists haven’t uncovered the exact relationship. Some—like Houpt, who has seen multiple cribbing horses die from colic during her research—believe cribbing causes colic. Others—like Seabra—suspect the colic and the cribbing share common origins, such as stress and diet. “Management factors would likely cause both these problems,” Seabra says.

7. It’s associated with higher sensitivity to touch and different learning styles.

Because some researchers wonder whether cribbing is related to horses’ personalities and the way they perceive stressful situations, Briefer and her colleagues ran personality testing on 19 cribbing and 18 noncribbing horses in Switzerland. They found no real differences in the animals’ curiosity, fearfulness, or reactivity to humans or other horses.

In another study, researchers confirmed cribbing horses learn basic cue-response tasks—such as touching a card to get a food reward—faster than noncribbers. However, they take longer than noncribbers to stop trying for that reward, continuing to touch the card well after it no longer leads to a food reward. This suggests “accelerated habit formation,” the U.K. team reported.

However, cribbers were significantly more reactive to being touched with a fine filament—a measure of tactile sensitivity. That might be because their altered brains have made them more sensitive. It might also be a reflection of their personalities that make them more sensitive in general and, thus, more likely to develop stereotypies when faced with chronic stress, they say.

More recently, Briefer and her colleagues reported both cribbers and noncribbers performed equally well learning to go around barriers to get food—even when the food location changed and had to be relearned. The cribbers might have managed well because they were allowed to crib during the tasks—and many did so when they appeared “frustrated,” she says. Because cribbing was associated with reduced cortisol, the researchers suspect these horses had reduced stress levels and could, therefore, learn better.

The findings overturn previous beliefs that cribbers are cognitively impaired, Houpt says.

8. Products like cribbing straps and slow-feeders might offer low-stress solutions.

Because cribbing is a stress-coping mechanism, not all researchers agree it should be stopped. But to avoid potential health risks, owners should aim to at least reduce its frequency when it’s ethical to do so, our sources say.

Ideally, that means removing stressors that provoke the stereotypy, especially by offering horses plenty of forage, free time outdoors, and interactions with other horses and by weaning less abruptly, Seabra says. When that’s not possible—or when cribbing is so ingrained the horses won’t stop—­owners might consider anti-cribbing equipment.

In her research Houpt found that cribbing collars didn’t stress her study horses—­although the animals might simply have gotten used to wearing them over the years, she says. She also found that a “tongue twister” toy with a sweet ball inside effectively reduced cribbing rates because the horses stayed busy licking the toy.

Italian researchers observed that cribbers spent significantly less time cribbing when they received concentrate or hay in a slow dispenser. And Seabra’s team has a forthcoming study comparing different slow hay-feeders’ beneficial effects on equine behavior.

The best scenario, of course, is to avoid the stereotypy altogether through good welfare from the earliest age, Seabra adds. “Because once they develop it, they will likely do it for the rest of their lives, especially when they are stressed or anxious,” she explains.

9. It resolved almost entirely in a test horse treated with CBD.

Cannabidiol (CBD) is a compound that acts on the central nervous system. Because of cribbing’s association with the brain and dopamine, Italian researchers suspected CBD might calm the intensity of the stereotypy. So they treated a 22-year-old mare with a standard dose of CBD every day. She had been cribbing 15 hours per day and had poor body condition and coat quality.

After 30 days of treatment the mare was cribbing less than an hour a day, had gained two body condition scores, and had developed a “shiny and silky” coat. The researchers suspect the CBD might be working on serotonergic and dopaminergic receptors in the brain and might also be reducing anxiety and, therefore, the drive to crib, they say.

While cannabis-derived veterinary medicinal products are not currently authorized for use in the European Union or North America, certain human medicinal products are sometimes permitted for use in animals in specific situations requiring veterinary guidance, they add.

10. Cribbing is not something horses learn from other horses.

A common misconception about cribbing is that horses pick it up from seeing other horses do it, our sources say. So far, there’s just no evidence to prove that.

On the contrary, researchers have noted anecdotally that horses don’t learn cribbing from each other.

“Whenever I give talks, I ask people to raise their hands if they have a horse that cribs,” Houpt says. “And then I say, ‘How many have a second horse that wasn’t cribbing and then started cribbing around that horse?’ and usually it’s about one person in the whole audience.”

Believing that cribbing is socially learned can cause serious welfare issues for the cribber, she adds, because those horses then get isolated to prevent “spreading” the behavior. “And, of course, isolation is stressful,” she says. “People need to realize that horses don’t learn to do it from other horses.”

The belief probably says more about humans than horses, Briefer Freymond adds. “The reality is, if you’ve got several stereotypic horses in the same stable, you need to consider what’s going on with the management there,” she says.

Take-Home Message

Cribbing continues to be a developing area of equine research. As scientists progress in their investigations, their focus shifts more toward the welfare issues that instigate the stereotypy and those that arise from how we view and manage it. By understanding that horses can’t help cribbing once they start, it doesn’t make them poorer learners, and its development is likely a reflection of our own management decisions, we might finally start to reduce its prevalence. “The correct approach is to let that horse be a horse,” Seabra says. “But people often don’t see that their horses are struggling. We need to change the way people think.”

Next Generation Sequencing (NGS) is a DNA/RNA sequencing technology commercially available since 2005 that overcame the limitation of traditional Sanger sequencing. Traditional Sanger sequencing was a targeted approach that could sequence a few thousand nucleotides at a time, while new sequencing technology allows for massive parallel sequencing of multiple genomes, often referred to as metagenomics. While different distinct approaches such as whole genome sequencing (WGS), targeted next-generation sequencing and shotgun metagenomics NGS exist for infectious disease diagnosis, the shotgun metagenomics approach provides hypothesis-free infectious disease detection and a comprehensive way to identify pathogens directly from clinical samples.

Classical culture-based pathogen detection has limitations as many pathogens grow poorly or not at all in culture. Similarly, newer molecular diagnostic assays (like PCR) rely on some prior knowledge of suspected pathogens, meaning that novel pathogens could remain undetected in such assays. Metagenomics-based sequencing has an advantage over traditional diagnostic assay, as it uses a “search for all” approach. In this approach, genetic material (DNA/RNA) from a clinical sample is subjected to metagenomic sequencing, resulting in millions of copies of genetic material of any microorganisms present in the sample. This data is then analyzed using sophisticated software tools to characterize the genetic material of microorganisms in the sample and in what proportion. This data, along with clinical history and other pathological changes, can help to identify disease-causing organisms, even if they were unexpected or novel to this type of clinical case.

Below are some of the applications of NGS in clinical diagnostics:

1. Broad-spectrum pathogen detection: Shotgun metagenomics is particularly useful in cases where the infectious agent is unknown and/or unculturable. It has been successfully applied in diagnosing infections caused by rare, novel or unexpected pathogens that might be missed by conventional diagnostic methods. For instance, we have recently discovered a novel rotavirus B causing life-threatening diarrhea in neonatal foals, where traditional diagnostic assays, such as bacterial aerobic and anaerobic cultures and PCR tests for Clostridium perfringens, Clostridioides difficile, Cryptosporidium spp, Equine Coronavirus and Equine Rotavirus A, were negative.

2. Polymicrobial infections: Traditional culture-based methods often struggle to identify all the pathogens involved in polymicrobial infections (those infections with multiple microbes of importance). Shotgun metagenomics can detect multiple pathogens in a single sample, providing a comprehensive picture of the disease. This capability is especially important in conditions like disease complexes, such as bovine respiratory disease complex, where timely and accurate identification of all the causative agents is critical for effective treatment.

3. Antimicrobial resistance: Beyond identifying pathogens, metagenomics can also detect any drug resistance present in the pathogen, for instance antimicrobial or antiviral resistance. By analyzing genetic material from the involved pathogens, we can identify resistance mechanisms and tailor antibiotic therapy accordingly. This is particularly valuable in the era of increasing antibiotic resistance, where inappropriate use of antibiotics can lead to treatment failures and further resistance development.

4. Outbreak investigation and disease surveillance: In outbreak settings, shotgun metagenomics can provide rapid and detailed insights into the causative agents and their transmission dynamics. It enables public health officials to identify the source of the outbreak, track its spread and implement control measures more effectively. Metagenomics approaches can also be used for disease surveillance and early detection. This approach was extensively used during the COVID-19 pandemic where wastewater surveillance was used for new variant detection. We can also determine whether mutated pathogens can escape the antibody response induced via vaccination by comparing the genetic makeup of the pathogen to that of vaccine strains. Pathogen typing, for instance Salmonella serovar identification or rotavirus genotyping, is an added advantage of this approach and can help clinicians formulate appropriate treatment plans.

Beyond infectious disease, metagenomics sequencing can also be used for noninfectious diseases. Detection of various hereditary diseases, genetic mutations predisposing individuals to certain diseases and early cancer risk prediction are some of the examples successfully used in human medicine.

Despite its advantages, shotgun metagenomics faces several challenges:

• Complex data analysis (bioinformatics): The incredible amount of data generated requires sophisticated bioinformatics tools and expertise to interpret. Differentiating between pathogenic organisms and commensal flora can be complex, especially in samples from sites with a high microbial load.

• Cost and time: While the cost has decreased significantly since metagenomic sequencing was introduced almost 20 years ago, it remains relatively high compared to traditional diagnostic methods, potentially limiting its widespread adoption. In addition, sequencing and data analysis can take several days, making rapid clinical treatment decisions difficult.

• Sensitivity and specificity: The sensitivity of shotgun metagenomics can be affected by the presence of host DNA, which may overshadow microbial sequences. Additionally, a pathogen of interest may not be detected if it is in low abundance in the specimen or the nucleic acid quality has degraded.

Nevertheless, metagenomics approaches for infectious disease diagnosis have been successfully applied to clinical samples like blood, respiratory swabs, bronchoalveolar lavage fluid, transtracheal washes, cerebrospinal fluid, brain tissue and fecal material and fecal swabs, as well as a variety of other body tissues and fluids. Overall, metagenomics-based NGS holds massive potential for infectious disease diagnosis in veterinary medicine and with the continual development of newer sequencing technology, both cost and time for sequencing are expected to decrease further.

Editor’s note: This is an excerpt from Equine Disease Quarterly, Vol. 33, Issue 4, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Tirth Uprety, DVM, MS, PhD, section head, and veterinary virologist at the University of Kentucky’s NGS Laboratory, in Lexington, and Erdal Erol, DVM, MS, PhD, professor, and head of diagnostic microbiology, at the University of Kentucky.

Late-gestation abdominal pain in mares can be a perplexing enigma, a blend of mystery and urgency

A horse of any sex or reproductive status could experience abdominal pain from gastrointestinal (GI) distress or muscle pain in the abdomen. But a pregnant mare showing abdominal discomfort could be aborting her fetus or developing pregnancy complications.

Most colics resolve uneventfully: no surgery or even fluids needed. “Abdominal pain is common in horses in general,” notes Ashley VanderBroek, DVM, Dipl. ACVS-LA, assistant professor of large animal surgery at Michigan State University (MSU) College of Veterinary Medicine, in East Lansing.

When it comes to dealing with pregnant mares, “I would say the majority of colic cases are similar to horses that are not pregnant—usually mild and resolve on their own,” VanderBroek says. However, when a pregnant mare’s colic becomes severe, it might require “prompt surgical management.”

Causes of Late-Gestation Colic

“Colic is just a term to describe abdominal pain in the horse,” VanderBroek explains. “Most of the time that’s associated with the GI tract, but it doesn’t have to be.”

“We have to think about the GI tract, urinary tract, and reproductive tract when a horse is displaying signs of colic,” adds Julie Strachota, DVM, MS, Dipl. ACT, assistant professor and director of clinical education at MSU’s College of Veterinary Medicine.

In late gestation space is scarce in the abdomen. So, in a pregnant mare experiencing abdominal pain, “some of it could just be discomfort from everything being a little bit more compressed,” VanderBroek says.

When the mare’s internal organs get compressed and displaced, diagnostics become challenging.

“It is very, very hard to call some of these ‘GI problems’ just based on palpation or based on ultrasonography,” says Ahmed Tibary, DMV, MS, DSc, PhD, Dipl. ACT, professor emeritus in the Department of Veterinary Clinical Sciences at Washington State University College of Veterinary Medicine, in Pullman.

With abdominal distress veterinarians often discern first whether surgery will be necessary. The precise diagnosis comes later.

Gastrointestinal Colic

Notable GI colic types in pregnant mares include a large colon volvulus (rotation of the bowel), cramping from gas, and impactions in or displacements of the large colon.

A large colon volvulus occurs when the colon rotates and tightly twists around on itself, VanderBroek explains. It is more commonly seen immediately post partum. “That is the most fatal form of colic, and broodmares, particularly, are predisposed to that.

“They are violently painful, like intractable pain,” she says. Getting close enough to administer sedatives safely can be difficult.

Sometimes the colic is just gas.

“Gas is produced during digestion, so the colon needs to be able to expand,” VanderBroek says. But when there’s a “big gravid uterus,” a little gas can lead to discomfort more quickly.

“Of the GI causes (of colic in late-gestation broodmares) approximately half are medical,” meaning they can be treated without surgery, says Julie Dechant, DVM, MS, Dipl. ACVS and ACVECC, professor of clinical equine surgical emergency and critical care at the University of California, Davis, School of Veterinary Medicine. “Of those needing surgery, almost 80% are strangulating lesions.” Those are mostly found in the large intestine.

Pregnancy-Related Colic

Notable pregnancy-related colic includes uterine torsion, abortions or dystocias (difficult births), hydrops (fetal fluid accumulation in the uterus), tearing of the abdominal wall, and uterine artery bleeding.

“Uterine torsion and uterine artery bleeding each account for approximately 5% of late-gestation colic,” Dechant says.

Uterine Torsion occurs when the mare’s uterus twists on its axis, potentially cutting off blood supply and damaging the placenta. It occurs more frequently during the final three months of gestation, Strachota says.

 Veterinarians diagnose uterine torsion using transrectal palpation, which they use to check the severity and direction of the twist, Tibary says.

Mares with uterine torsions usually display mild to moderate abdominal discomfort, Strachota says. They might lie down more, have a decreased appetite, or defecate less than they should.

Cases of late-gestation mares showing signs of colic can present another issue: premature foals. These foals face such long odds that VanderBroek says she avoids delivering them early.

“If I take a mare to surgery for a uterine torsion, even if her due date is next week, I will correct the torsion, and I will leave the foal in the uterus,” VanderBroek says.

Abortion and parturition (giving birth) have similar clinical signs and can include vulvar discharge, relaxation of the prepubic tendon, and mammary development. Nesting in the stall, eating less, or isolating from other horses are other signs, Strachota says.

Dystocias can occur with live foals but are more likely if a fetus dies in the uterus.

“Horses have to be born a specific way,” with head and legs extended, VanderBroek explains. If the head or legs are bent instead of in a “forward dive” position, the mare might have difficulty delivering.

Hydrops is rare but “one of the most critical as far as emergencies,” Tibary says. Hydrops occurs when an abnormally large amount of fetal fluid accumulates in the mare’s uterus.

“The last case I had was 230 liters of fluid,” Tibary says. “That’s 230 liters pressing on the diaphragm.”

Respiratory distress can be a sign of hy- drops, he says, or they are a downer mare—one that is lying down and unable to rise.

Muscle Tone and Age can contribute to colic risk, with aging mares or those with pituitary pars intermedia dysfunction (PPID, formerly equine Cushing’s disease) particularly vulnerable.

“PPID generally compromises the abdominal muscle tone and, as they get heavier toward the end of pregnancy, they may have ruptured muscles or prepubic tendon rupture,” Tibary says.

Monitoring the Mare for Colic

Typical signs of colic include pawing, flank-watching, and rolling. But late-gestation mares can show broader signs, Dechant says. Watch for “changes in attitude (agitated or dull), changes in manure consistency (loose or dry), decreased or absent manure output, reduced or absent appetite, and lying down more often.”

Watch the udder “for premature signs of udder development or dripping of secretions. Vulvar discharge or development of abdominal edema or swelling are also important to monitor,” she adds.

Dechant further recommends owners learn to take their horse’s vital signs (temperature, heart rate, and respiratory rate). Late gestation mares often have mildly increased heart rates and respiratory rates. Sudden or moderate-to-severe increases in heart rate or respiratory rate are not normal, she says.

Call the veterinarian when you see obvious signs of discomfort; mild signs of discomfort that last more than one to two hours; or multiple simultaneous signs (such as mild discomfort in addition to not eating or abnormal vital signs).

Treatment Options for Late-Gestation Colic

The mare’s treatment depends on the diagnosis, of course. For late-gestation colics that get sent to the clinic, approximately half respond to medical treatment, while half require colic surgery, Dechant says.

“Some problems, such as uterine torsion, have different treatment options depending on the clinical signs, gestation length, and clinician preference,” Dechant notes. “Some problems, such as hydrops or body-wall tears, require confinement, analgesia, and abdominal support wraps.”

For other problems causing abdominal pain, the mare might need medication to fight infection or prevent pregnancy loss, Dechant says.

GI Colic Treatment

Mares with a large colon volvulus need to go straight to surgery; time is critical.

“The sooner they can get to a hospital, the sooner they can get anesthetized, the sooner that they can get on the table, the more likely they are to survive,” VanderBroek says. If it takes three or four hours to arrive at the hospital, “the likelihood that they’re going to survive decreases.”

For other kinds of GI colics, treatment might include administering non-steroidal anti-inflammatory drugs (NSAID) for pain; using a nasogastric tube to check for reflux; or administering fluids, Strachota says.

VanderBroek notes that pain plays a role in determining whether a case needs to go to surgery. Compromised blood supply is another factor. If something’s twisted or strangulating, “I recommend surgery because that’s going to be the only fix,” she says. “You cannot resolve a large colon volvulus or another strangulating lesion medically. There’s just no way to do that.”

Pregnancy-Related Colic Treatment

If your mare has uterine torsion, a veterinary team might attempt to roll the mare using the “plank on the flank” technique.

The veterinarian using this method first determines the direction of the twist—counterclockwise or clockwise. Next, after anesthetizing the mare, placing her on her side, and setting a wood plank on her belly in a specific area (TheHorse.com/124561), someone kneels on the plank, while other handlers roll the mare to her other side. The person kneeling holds the uterus still while the mare is rolled to correct the torsion.

The technique proves successful about 80% of the time, Tibary says. To attempt it veterinarians must know both how to perform the maneuver and the direction of the torsion.

“If you start rolling the mare every which way, and you don’t know the direction of the torsion, you could rupture the uterus,” Tibary says.

Veterinarians can also address torsions surgically.

“Mare survival is approximately 85-90% and up to 80% live birth rates if the mare is less than 320 days gestation, and the mare is not in shock or compromised,” Dechant says.

Prognosis After Treatment

Survival rates after colic surgery in late-gestation mares average 60-65%, slightly lower than rates in nonpregnant horses, Dechant says.

When the mare survives, “approximately 75% of these cases can have successful pregnancy outcomes” depending on the severity, she adds.

Mares with hydrops have an excellent survival rate, provided they do not have body wall tears or go into shock, Dechant says, though they typically lose the fetus. But in many of these cases, mares can be successfully rebred and deliver foals naturally.

Preventing Late-Gestation Colic

Preventing GI Colics

“Owners will say, ‘What can I do to ensure that my horse never colics?’ and my response is, ‘Don’t get a horse,’ ” VanderBroek says. “Because there’s no way to completely prevent colic.”

Still, our experts have some advice:

• Ensure horses have hay in front of them all the time so they eat throughout the day. “If the colon is full of fiber when it twists, it doesn’t compromise the blood supply quite as much,” VanderBroek says. “Horses were not meant to eat large grain meals twice daily.”
• Feed pregnant mares and lactating mares according to their body condition and their actual energy demands, says Strachota. This will ensure they receive balanced nutrition, which supports their gut health and reduces the risk of digestive disturbances.
• If you make changes in feed and management, do it gradually to help the sensitive bugs in the gut adjust.
• Hydration can prevent impactions. Try flavored electrolytes if your mare needs more water, Strachota says.

Preventing Pregnancy-Related Colics

Some pregnancy-related colics have unknown causes.

Uterine torsion is “bad luck,” VanderBroek says; there’s nothing you can do to prevent it.

Theories exist about the cause of hydrops but “we don’t really know,” Tibary says.

Strachota emphasizes the role of biosecurity in preventing abortion. Mares should be isolated from animals that have left the property and returned, and they should be kept away from high-traffic areas.

Tibary stresses the importance of checking a mare’s pregnancy early because twin pregnancies are “something that is either going to result in abortion or result in some pretty serious problems.”

If your veterinarian finds one embryo but the ovaries show more than one ovulation during the first pregnancy check, you might need to check again later, he says. Vets should examine the mare at five months of gestation to verify everything is normal. These checks can identify problems that could lead to abortion, such as a thickening or separation of the placenta.

Take-Home Message

Late in pregnancy, mares’ abdominal space is a limiting factor, and they can experience colic, whether due to gastrointestinal problems, uterine torsion, abortion, or dystocia.

“There are other possible causes for colic, but those three come to my mind first,” VanderBroek says. Deciphering a mare’s clinical signs can be tricky and time matters, so call the veterinarian sooner rather than later.

This article is from the Winter 2024 issue of The Horse: Your Guide to Equine Health Care. We at The Horse work to provide you with the latest and most reliable news and information on equine health, care, management, and welfare through our magazine and TheHorse.com. Your subscription helps The Horse continue to offer this vital resource to horse owners of all breeds, disciplines, and experience levels. To access current issues included in your subscription, please sign in to the Apple or Google apps OR click here for the desktop version.