Menlo Park, CA – Etalon Equine Genetics, a leading provider of equine DNA testing services, has made another exciting breakthrough in equine genetics. Their research team, led by Aiden McFadden and Katie Martin, has identified two novel variants in the MITF and PAX3 genetic regions that are strongly associated with blue eyes and the “Splashed White” phenotypes in horses. The findings have been published in the Journal of Equine Veterinary Science.

Splashed White in horses is characterized by a coat color spotting pattern that appears the animal may have been dipped in white paint. Previous studies have linked this unique phenotype to specific variants in the PAX3 and MITF genes, which play crucial roles in melanocyte migration and pigmentation. Etalon Equine Genetics has discovered two new mutations in a group of Pura Raza Española (PRE) horses owned by the Gil Torrano family from Yeguada Sierra de la Espada.

These particular horses exhibit striking markings that include Splashed White patterns and distinctly blue eyes; both are highly uncommon among PRE horses. Genetic analysis revealed that these horses did not carry any previously known white alleles, including any formerly associated with the Splashed White family of mutations. Upon discovery of the new variants, the research team proposed nomenclature and designations of Splashed White 9/Giltor (SW9) and Splashed White 10/Giltor (SW10), paying tribute to the Gil Torrano herd in which they were discovered.

These new findings further our knowledge for the genetic basis of coat color as well as health and performance variants in mammals. This understanding can greatly contribute to the development of selective breeding programs specifically designed to preserve and manage remarkable and distinctive traits in horses.

Research is ongoing in an effort to fully understand the implications of these mutations and how far reaching they may be in other horse breeds or, possibly, other species. However, this discovery represents a significant advancement in the field of equine genetics, providing valuable insights into the complex mechanisms governing melanocyte migration, pigmentation, heritability and genetic diversity.

For more information or media inquiries, please contact Etalon Equine Genetics at info@etalondx.com or 650.380.2995. High-resolution images are available upon request.

About Etalon Equine Genetics

Etalon Equine Genetics is a leading provider of equine DNA testing services. With a commitment to advancing the understanding of equine genetics, Etalon Equine Genetics offers comprehensive testing solutions to horse owners and breeders worldwide.

Immune-mediated myositis is a muscle disease seen in Quarter Horses and related breeds such as Paints and Appaloosas. It can lead quickly to muscle weakness and atrophy and can leave your horse feeling generally ill. Unfortunately, not a lot has been known about the cause of IMM. New research, though, shows there is likely a genetic link.

A team led by Carrie Finno, DVM, PhD, DACVIM, assistant professor in the department of population health and reproduction at the University of California, Davis, set out to examine genetic aspects of the disease. The team included Stephanie J. Valberg, DVM, PhD, DACVIM, ACVSMR, from the department of large animal clinical sciences at Michigan State University, and colleagues from both universities as well as from the University of Minnesota.

The researchers gathered DNA samples from three groups of horses:

• 36 Quarter Horses with a history of IMM
• 54 Quarter Horses with no history of IMM
• 175 horses from 21 other breeds.

Each group was a mix of geldings, mares and stallions with approximately the same average age range. All were housed in the same environment. Any horses with polysaccharide storage myopathy (another muscle disease particularly found in Quarter Horses) were excluded from the study. None of the horses were related to each other within at least one generation.

After extensive analysis of the DNA samples, the team identified a mutation in the MYH1 gene. This gene is related to the protein myosin, which plays a role in muscle contraction. The mutation affected 14 different amino acids in the protein. Specifically, it appeared to destroy Type II (slow-twitch) muscle fibers, leading to the disease’s characteristic muscle atrophy.

Notably, the mutation was not found among the 175 horses from non-Quarter Horse breeds. This supports the idea that IMM may be an issue only for Quarter Horses and related breeds.

The researchers also analyzed the horses’ pedigrees and found that certain stallions were heavily represented among the horses showing the mutation, indicating that IMM has a genetic component.

However, researchers do not necessarily believe that the MYH1 mutation directly causes IMM. Rather, horses with the mutation are more likely to experience active symptoms of the disease under certain circumstances. For instance, this could include age, as IMM is more likely to affect horses under age 8 or over age 17. And, according to past studies, there may also be a connection between IMM symptoms and a recent history of certain types of infections or vaccinations.

On the bright side, IMM-affected horses generally regain full muscle mass after one to 10 weeks of corticosteroid treatment.

This article was originally published in the September 2018 issue of Practical Horseman. 

With the 2018 FEI World Equestrian Games Tryon quickly approaching, now is a great time to reflect on the incredible amount of training, dedication and passion that the athletes competing have invested to reach this level. We are all familiar with the outstanding feats of coordination between horse and rider that culminate in world-class performances in the ring, however, sometimes we don’t consider all of the ‘behind-the-scenes’ work that makes this possible. As a fan of show jumping, as well as someone working in the industry, I have always been fascinated by the steps needed to reach the top. I have performed a number of analyses quantifying currents trends in competition and training theory, and have been lucky to discuss my thoughts with some of the top horse people in the world.

In this series, I will provide an overview of some often-forgotten yet important considerations for producing a winning round at a major show-jumping championship. I will discuss recent exciting scientific findings around these concepts, and I will share my two cents on where I think the future of the sport may be heading and the potential role of technology in this evolution.

Each year thousands of sporthorse foals are conceived with the goal of producing the next top horse. With respect to horses bred for show jumping, only a small proportion of these horses will go on the reach the grand prix level, and the odds of having a horse win a medal at a major championship are similar to buying a winning lottery ticket.

To improve the likelihood of producing a top horse, breeders will methodically choose bloodlines to acquire “optimal” genetics for their horse. Further, once the foal is born, top breeders will put the young horse in the best possible environment, ensuring high-level training, an outstanding and safe living environment, proper nutrition, top veterinary care and so on. With this approach, breeders attempt to optimize both nature (genetics) and nurture (the environment).

Despite this thorough planning and the best efforts of everyone involved, the horse may still not reach the pinnacle of the sport. Interestingly, recent scientific evidence has linked the environment of the mare at both conception and during pregnancy as an important factor that can have lifelong implications for the foal. It is possible that these factors, which are typically not given much thought when the mare is carrying the foal, may be contributing more to the health and performance potential of the foal than originally thought.

Termed ‘Developmental Origins of Health and Disease’, the conditions the foal is exposed to from conception through pregnancy and to the neonatal period can modify the expression of genes (while the DNA remains unchanged). Examples of factors that can influence the developing foal in dams include elevated stress and improper nutrition. Thus, a dam exposed to suboptimal conditions in one of these factors can produce negative changes to the in utero environment for the foal, and consequently changing how the developing horse expresses certain genes.

For example, two recent studies have linked the development of osteochondritis dissecans in young horses to the nutrition their dams received during pregnancy. OD is defined as a disease in which the cartilage at the ends of bones, especially long bones, fails to develop properly—leading to a lesion in the cartilage that may or may not dislodge. The disease presents in young horses, and arthroscopic surgery is the current standard of care to return horses to work. Researchers have found that pregnant mares fed diets high in concentrate produce foals with OD at a higher rate than dams fed forage only diets.

Does this mean that all pregnant mares should be on forage only diets? The answer is: No. Understanding how developmental conditions influence horses is an incredibly complex area that is multifactorial and dynamic. Although OD is linked to a lower prevalence in pregnant mares fed only forage, other studies have found that a forage only diet produced foals with thinner canon bones (potentially indicative of weaker bone) and foals predisposed to issues regulating blood glucose. So as you can see, diets of both extremes (forage only vs high in concentrate) are both linked to issues, and a proper diet will be a happy medium. That said, each dam is an individual and will have slightly different needs, but determining those needs accurately remains a challenge.

The Future

To help answer the question of “what nutrition is best for a dam?,” advancements in our understanding of developmental origins of health and disease will begin to play a larger role in how pregnant dams are cared for. Using the knowledge researchers produce, it is likely that each dam will eventually have a custom nutrition plan based on a quick test. The test could be a simple blood test, whereby certain markers in the blood determine exactly what feed is needed to optimize in utero conditions for the developing foal. Further, the same blood test could detect markers of chronic stress, and again actions could be taken to remove the stress before it has harmful effects on the developing foal. Armed with this information, we will eventually be able to increase the likelihood of producing horses with better health.

Dr. Tim Worden is a consultant for Hylofit and specializes in the translation of human high-performance training theory and techniques to equestrian athletes. With expertise in both equestrian sport and sports science, he is uniquely positioned to move training techniques from ‘human to horse’; improving the performance of horses and reducing injury risk. Tim completed his MSc (Biomechanics and Neuroscience) and PhD (Biomechanics) at the University of Guelph, Canada. He has published a number of peer-reviewed articles on human navigation through complex environments and the control of stability during locomotion. During his time as a doctoral student, Tim concurrently worked as an equestrian sport scientist, with a clientele composed predominantly of FEI-level show jumping riders. Follow him on Instagram – @twordentraining. 

Hylofit is sponsoring Practical Horseman’s show-jumping coverage of the 2018 FEI World Equestrian Games Tryon.

What if you could view X-rays of a young foal and predict problems that he might have as an adult? That might give you time to take supportive measures to prevent the problems from occurring.

That was essentially the goal behind a study conducted by Elizabeth M. Santschi, DVM, DACVS, professor of equine surgery at Kansas State University’s College of Veterinary Medicine, and her team. They wanted to determine if incomplete formation of minerals required to grow healthy bones (mineralization), in this case knee and hock bones, in foals could predict problems later in life—such as deviations in limb straightness, misshapen bones and osteoarthritis—that can negatively affect athletic performance.

For the study, researchers selected 100 full-term Thoroughbred foals living on horse farms in central Kentucky. The team reviewed X-rays of the foals’ knee and hock joints taken during their first week of life and again at 110 to 301 days of age.

In the first-week X-rays, researchers evaluated the level of mineralization of the joints’ cartilage that would eventually turn into full-size bone (cuboidal bone growth cartilage). They found that mineralization was complete in only 46 percent of the foals.

The team then reviewed the X-rays taken when the foals were older and identified any abnormalities. In comparing their findings from the younger and older X-rays, the researchers discovered that foals whose joints had not fully mineralized tended to demonstrate abnormalities (like those mentioned above) in their hocks at the later age. Interestingly, no such relationship was shown in the knee joints.

The researchers concluded that there is an association between lack of mineralization and later issues, at least in the hock joints. Since X-rays can show incomplete mineralization in very young foals, they could be useful in early identification of potential trouble. And that, says Dr. Santschi, would allow the foal’s owner to initiate measures—such as limiting exercise for the youngster—that could help reduce the risk of future problems.

This article was originally published in the June 2018 issue of Practical Horseman. 

Just as the days are beginning to grow longer and you’re anticipating more time to ride, you notice that your normally sweet mare is becoming increasingly cranky. She’s difficult under saddle and her pinned-back ears warn you to back off. From time to time, she stomps her feet and squeals for no apparent reason. You consider whether she’s ill or injured, but know that there’s a much more likely cause of all the fuss: She’s in heat and exhibiting some of the typical mare-ish behavior associated with an increase in the activity of her reproductive system.

It helps to know that it’s just a matter of time before she cycles back to normal. But you wonder what you might do to ease her through the hormonal swings that can cause physical discomfort as well as fuel undesirable behavior. Several medical treatments and supplements may offer relief. Plus, experienced professionals point to the benefits of conscientious management to take at least some of the stress out of estrus. To determine the course of action that’s right for your mare and you, it’s worthwhile to first understand what’s going on inside her.

The Biological Basics

Female mammals of many species have a reproductive cycle that includes a recurring period of sexual receptivity (estrus). For horses the natural breeding season occurs in the spring and summer. During this time, mares ovulate every 21 days and are in estrus for five to seven days. In the winter months they experience a period of sexual inactivity (anestrus).

“Normal cyclicity in mares is dependent on the onset of longer day lengths,” says Charles Love, DVM, PhD, Dip ACT, professor of equine theriogenology at Texas A&M University. Specifically, the increase in daylight that is a hallmark of spring signals the pituitary gland at the base of the mare’s brain to release what is known as follicle-stimulating hormone into the bloodstream. FSH travels to the ovaries, where it initiates the development of a cavity, or follicle, containing an egg (ovum). As the follicle grows on an ovary, it produces the hormone estrogen. At a certain point, the level of estrogen in the blood signals the pituitary gland to secrete a second hormone. This one, luteinizing hormone, triggers ovulation, causing the follicle to rupture and send the egg into a fallopian tube, the passageway where it may be fertilized as it makes its way to the uterus.

Once its contents are released, the follicle forms a temporary structure called the corpus luteum. It functions for approximately 12 to 14 days, secreting some estrogen and relatively high levels of the hormone progesterone to sustain pregnancy. In those instances where conception does not occur, the hormone prostaglandin—which is released by the uterine wall—causes the corpus luteum to be reabsorbed into the ovary. In turn, the level of progesterone decreases and the estrus cycle resumes. If, however, the mare conceives, the activity of the growing embryo in the uterus halts the release of prostaglandin. As a result, the corpus luteum remains functional and progesterone levels are maintained so that the pregnancy continues.

“When the mare ovulates she will remain in heat one to two days after and then will go out of heat,” Dr. Love explains. During that time she may display a variety of signs—usually when she’s around other horses, especially males—to indicate she’s receptive to a stallion. They include lifting her tail, squatting, urinating and “winking”—opening and closing the lower part of the vulva, the outside portion of her genital tract.

Beyond the behaviors that signal she’s ready to breed, a mare in heat may also exhibit some degree of change in attitude and performance—but not all mares do. The most common behaviors are tail swishing, squealing and kicking as well as excessive urination. In addition, physical discomfort from the pain of a developing follicle may cause a mare to be uncooperative and hard to ride or train, leading to decreased performance under saddle.

“Most mares are difficult in heat due to the constant urination and the distraction of being around other horses,” Dr. Love says. “Some mares do exhibit ovarian pain and may actually colic as a result.”

For these reasons and others, it’s natural for a concerned owner to turn to the offerings of modern medicine in search of a remedy to ease the ill effects of estrus.

A Measure of Control

A variety of medications, supplements and procedures are available to suppress or eliminate estrus, ensuring little to no change in a mare’s temperament and behavior throughout the year as well as consistency in performance during training and competition. None of the treatments that follow should be used without first consulting a veterinarian to evaluate merits and potential drawbacks for each individual mare. Here are several of the most common options.

Altrenogest (Regu-Mate) is an FDA-approved progestin (synthetic progesterone) prescribed by a veterinarian. It is administered orally—either in feed or put directly on a mare’s tongue using a syringe—on a daily basis at a cost of approximately $23 per dose. It increases the level of progesterone in the blood and blocks ovulation, keeping a mare out of heat for as long as the medication is administered. Altrenogest is readily absorbed through skin so it must be handled with care so that it does not affect the person dispensing it. It carries the warning to always wear gloves when handling the drug and not allow it to contact eyes, skin or clothes. Because it can be harmful to their own cycles, premenopausal and pregnant women are advised to exercise extreme caution when handling altrenogest.

Medroxyprogesterone acetate (MPA, Depo-Provera) is a synthetic derivative of the hormone progesterone and is used to suppress ovulation in women. It is not FDA-approved for use in horses. However, a veterinarian may prescribe the drug to reduce a mare’s estrus symptoms. Studies show that MPA, which is administered by injection, does not keep a mare from entering heat, but anecdotal evidence indicates that it improves behavior (see sidebar “What Role in Competition?”). Little is known about its long-term effects.

Dried raspberry leaf, according to anecdotal evidence, has been shown to reduce estrus symptoms when it’s provided as a daily supplement in feed. Long used by women to assist in maintaining a healthy pregnancy, the herbal remedy—which is not subject to the scrutiny of any regulatory agency—contains antioxidants and nutrients believed to relax muscle spasms and strengthen uterine tone. Raspberry leaf will not stop a mare from entering heat, but its effects may relieve the symptoms that lead to moodiness.

Intrauterine marbles are reported to suppress estrus in some mares. Within 24 hours after ovulation, a veterinarian places a single sterilized glass marble in the uterus. At approximately 35 millimeters in size (just less than an inch), the marble tricks the body into thinking it is an embryo, which causes the uterine lining to alter its secretion of prostaglandin to maintain pregnancy. The success rate of using an intrauterine marble varies, but it is a relatively inexpensive option. Depending on the cost of the vet’s farm call and the marble, the total may reach a couple hundred dollars for an implantation that lasts six months to a year. The mare returns to a normal cycle when the marble is removed. Long-term use (beyond a year) is not recommended because it can invite complications, including uterine infection and inflammation of the uterine lining. It’s also possible for the marble or pieces of it to become embedded in the uterine lining. What’s more, a mare may expel the marble without her owner’s knowledge.

Spaying (ovariectomy) may be recommended in cases where intense ovarian pain cannot be relieved. The ovaries are surgically removed in a hospital setting with the mare under standing sedation. The procedure is expensive and carries some risk, such as hemorrhage and infection. In addition, although the mare will be permanently unable to conceive, she still may experience hormone-related behavior issues since estrogen is produced from sources other than ovaries, such as the adrenal glands.

“There are anecdotal reports of improvement following ovariectomy.” says Dr. Love, adding a caution: “Remember, once the ovaries are removed you can’t put them back. The owner should also realize once ovaries are removed the mare may exhibit signs of heat to some degree continuously, which is an unintended consequence.”

Dr. Love offers guidance for deciding the best course for a mare who seems to be adversely affected by estrus: “Too often the hormones of the mare and her cycle are blamed for poor performance,” Dr. Love says. He recommends determining “whether the mare performs well when out of heat. If so, that suggests that the problem is really heat-related.” However, “If the mare does not improve [when she no longer is in season], then other sources of discomfort should be investigated, such as ovarian pain, ulcer, musculoskeletal pain and rider inexperience. Mares will also show signs of heat [frequent urination, for instance] as a result of stress.”

A Focus on Behavior

In managing mares—or any horse, for that matter—John Michael Durr, a professional eventer and hunter/jumper rider, takes the approach that knowing them is key to doing right by them. With horses regularly coming and going from his training and sales barn in Shelby, North Carolina, he has handled a number of mares and developed his own successful strategy for dealing with them. The emphasis of his approach, he says, is to maintain a consistent training and management routine that allows him to really get to know the mares in his care so he can more readily identify when something isn’t right and determine the best way to resolve any issues.

“Keeping mares on a consistent routine will keep their stress levels down and make it more likely that you notice even a slight change in health or behavior,” Durr says. For instance, “I keep a close eye on fit and competing mares for signs of [gastrointestinal] ulcers and treat them if necessary. I also make sure they have well-fitting tack because they might be more sensitive to an uncomfortable saddle or bridle than a gelding will be.”

As a general practice, Durr won’t give a mare medication to control her cycle unless there are pronounced inconsistencies in her behavior on the ground and under saddle. As an example, he describes his experience with Esprit de la Danse (aka Dani) a Canadian Sport Horse mare he successfully evented at the three-star level. She grew so attached to her barn buddies when she was in season that she would pace and whinny for them instead of eat. As a result, she lost weight. Plus, she was constantly distracted, making it difficult to maintain consistency in her training program. After a thorough physical examination, the mare’s veterinarian prescribed OvaMed, an FDA-approved generic alternative to Regu-Mate, which was effective in reducing her attachment issues and stress levels during estrus.

“She was still a sensitive mare,” says Durr, but the medication helped to re-establish consistency in her behavior and allowed him to create what he describes as “a quantifiable system” for knowing how to plan for and prevent her disruptive episodes of fretfulness. He goes on to explain his approach: “I really try to give mares several breaks a year from any medications they are on to suppress their cycles. To me it’s important that they still get to have a healthy cycle. So when they are letting down from events, they come off the meds.”

What remains constant is Durr’s attention to their behavior and doing what he sees as necessary to keep them on an even keel. He notes that when traveling he is especially careful to set up a comfortable home away from home to reduce stress and increase the likelihood that a mare will get adequate rest so she’s ready for the rigors of competition. “Traveling is hard on mares,” he says. “We make all these accommodations for stallions when shipping, but the same factors have to be considered for mares.”

As a result, he won’t put a mare next to a stallion on a trailer, especially if she’s in season. He also avoids shipping a mare next to her best friend and refrains from putting them in adjacent stalls at competitions to lessen the possibility of attachment drama. In addition, he takes steps to minimize distractions at the front of a mare’s stall, doing what he can to reduce foot traffic and providing access to plenty of hay to keep her occupied.

A Tale of Two Sisters

Like Durr, Roslyn Johnson, an eventing horse breeder in Grantville, Georgia, has learned that there is no one-size-fits-all solution when it comes to managing a mare’s heat cycle. Each is an individual and is best treated as such. She offers her experience with two of her homebred mares as an example.

Full sisters Flo, age 14, and Kite, age 12, are seven-eighths Thoroughbred and one-eighth Irish Sport Horse. As youngsters they were both started under saddle by the same person and developed under the same training program. Each has evented through the Intermediate level. The only notable difference in their upbringing, Johnson says, is how Flo was handled as a foal. As the farm’s first homebred, Flo was spoiled and “mare-ish from the get-go,” she admits. In contrast, Kite’s upbringing was more disciplined, Johnson says, and she “is one of the sweetest mares you’ll ever meet. She has a good work ethic and is very consistent.”

Kite was never any trouble, even when in estrus, until one day at a competition. She was 7 at the time and started exhibiting cranky, opinionated behavior, which was totally uncharacteristic for her. She was refusing all over the place and dumped [her rider]. The vets at the show checked her out to make sure there weren’t any lameness issues.

Kite was pronounced sound, but her atypical behavior still concerned Johnson. So she trailered the mare to Auburn University’s John Thomas Vaughan Large Animal Teaching Hospital in Auburn, Alabama. A physical exam there included an ultrasound that revealed an enormous follicle in one of Kite’s ovaries that very likely was painful and the reason for her unusual behavior.

Ever since the episode, Kite has received Regu-Mate during the competition season with good results. Her sister Flo is on a regimen of the medication, too, because it was discovered that she also is prone to oversized follicles. Johnson reports that Flo’s behavior has improved as a result.

Though the sisters’ issues were resolved with medication, Johnson stresses, as medical experts do, the importance of a comprehensive veterinary evaluation to determine whether estrus—or something else—is at the heart of mare-ish behavior. Another upper-level event mare that Johnson owns seemed to experience physical discomfort during her cycle and, as a result, began receiving Regu-Mate. But unexpectedly, her ill temper worsened. So the treatment was discontinued and the mare’s behavior monitored. When she failed to improve, a veterinary exam revealed that she was suffering from a compensatory strain in her back. She was treated for her injury and has had no need for hormonal medication during her cycle.

The episode underscores the value of a truly objective approach to dealing with mares and with estrus. Knowing your mare when she’s in season and when she’s not will provide you with the best framework for evaluating the need for medical intervention when she’s in heat and out of sorts. It will also serve as a guide for making changes in how you care for and manage her and reflect your concern that any action you take is with her well-being in mind.

What Role in Competition?

There is some debate within the equestrian community on whether the two major substances commonly used to control estrus in mares and, in certain cases, the behavior of stallions and geldings have a place in competition. Some owners, riders and trainers say that using altrenogest and medroxyprogesterone acetate (MPA)—especially in stallions to manage potentially injurious behavior—creates a safer environment for all. Others believe the drugs are a more humane alternative to methods such as excessive longeing to quiet a horse before an athletic performance. But a number of other drugs that have a calming effect already are prohibited in competition. Where do the major organizations that regulate equine sports stand on altrenogest and MPA?

The International Equestrian Federation (FEI) prohibits the use of altrenogest in male horses and MPA in all horses during competition. US Equestrian (USEF) currently allows altrenogest to be used in mares during competition, but as of December 1, 2024, the use of any progestogens in stallions and geldings is now prohibited.

The organization began discussing regulation of these substances during its annual meeting in January 2017. In addition, in March of that year during a USEF public workshop, Patrick McCue, DVM, PhD, Dip ACT, a professor of theriogenology based at the Equine Reproduction Laboratory of Colorado State University, discussed the results of a study on the use of altrenogest and MPA in mares (“Efficacy of Medroxyprogesterone Acetate in Suppression of Estrus in Cycling Mares” by Erica K. Gee, BVSc, PhD, Dip ACT; Catherine DeLuca, DVM; Jessica L. Stylski, BS and Patrick M. McCue, DVM, PhD, Dip ACT).

The findings showed that those treated with altrenogest did not come into heat. In contrast, mares treated with MPA exhibited an increase in luteinizing hormone, developed follicles and ovulated. But so did mares who received a saline placebo, leading researchers to conclude that MPA does not have a biological effect on a mare’s estrus cycle and any improvement in behavior must come from some other effect of the drug.

With the findings in mind, US Equestrian concluded that more information was needed before a decision could be made. At its mid-year meeting in 2017, the Board of Directors approved a recommendation by its USEF MPA Panel to continue researching and analyzing the use of the drug in competition horses. The panel included trainer/judge Geoff Teall, USEF Vice President Elisabeth Goth, 2016 Olympian Laura Graves and Veterinary Committee Chair Kent Allen, DVM.

To support the ongoing research effort into MPA, a disclosure form became required for all horses—mares, stallions and geldings—receiving the medication within three months of a competition start date. The form tracked the dates when MPA was administered as well as the dosage.

This data, combined with an additional investigation by the MPA Panel, led to a December 1, 2019 ruling by the US Equestrian Board of Directors to prohibit the use of MPA in all horses competing in USEF-licensed competitions. According to US Equestrian, the MPA Panel determined MPA has no therapeutic use in competition horses, as it does not interrupt estrus in mares. Additionally, MPA is not approved by the United States Food and Drug Administration (FDA) for use in equines, and its use has been reported and documented to be associated with several cases of anaphylaxis and fatality. As a result of this analysis, the Panel voted unanimously to recommend MPA be added to the list of USEF prohibited substances.

“In 2017, we debated the use of this substance and its efficacy, but now, with numerous fatalities associated with the use of MPA, this decision became clear: MPA must be banned,” said USEF President Murray Kessler. “The information clearly supports the prohibition of this substance, and I am proud of the decision of the Board of Directors. USEF has a responsibility to ensure the welfare of our horses, and the loss of one horse resulting from the use of a non-therapeutic substance such as MPA is one too many.”

This article was originally published in the April 2018 issue of Practical Horseman, but has been updated according to new information published by US Equestrian.

Test-tube foals born from frozen embryos are no longer the latest news in equine reproduction. Not since a team at Ghent University in Belgium—led by professor Ann Van Soom, Nerea Ortiz Escribano, PhD, and Katrien Smits, DVM, PhD—welcomed VICSI, the world’s first foal born from a frozen, immature oocyte (egg).

“Previously, foals have been born from frozen oocytes,” Dr. Smits says. “But those were partially matured in the mare. So, it is the combination of freezing an immature oocyte and total in vitro production of the equine embryo after warming of the oocyte which is novel.”

Specifically, the Belgian team used two techniques, which also were combined to form the colt’s name. One was vitrification, a method of cryopreservation (freezing) that rapidly cools the oocyte in such a way that ice crystals, which can damage the oocyte, aren’t formed. Instead, the oocyte freezes into a glass-like structure.

Second, the researchers used intracytoplasmic sperm injection to directly insert sperm into the mare’s egg. This technique increases the probability of fertilization—even when the sperm is lower quality or in limited supply.

For the study, the researchers collected immature eggs, vitrified them and stored them in liquid nitrogen for one week. The eggs were then rapidly warmed and matured for nine days in an incubator. They were then fertilized by ICSI and cultured in the incubator for another nine days.

“Out of 179 vitrified oocytes, five embryos developed,” says Dr. Smits. “They were all transferred to recipient mares, resulting in two pregnancies. A first pregnancy was lost around 20 days. The other resulted in the birth of the foal.”

Despite the successful birth, the research team acknowledges that the technique isn’t yet ready for practical mainstream use. “With vitrified oocytes, the chance to get a foal is more than 10 times lower than with fresh oocytes,” says Dr. Smits. “Therefore, more research is needed to optimize the results prior to application.”

But the eventual results could be worthwhile. The vitrification of immature oocytes would allow genetic material to be transported to laboratories that otherwise wouldn’t have easy access to it. It could even give breeders more flexibility since they could postpone the decision on choosing a stallion, for example, until more information is available on the results in sports competitions, says Dr. Smits. “Finally, vitrification of immature oocytes can also provide the opportunity to conserve female genetics for gene-banking of endangered breeds or species.” 

This article was originally published in the January 2018 issue of Practical Horseman. 

A horse’s metabolism can slow down when the weather gets cold. It’s one way the horse’s body can realign resources to stay warm. With modern breeding practices often manipulating mares’ natural reproductive cycles to deliver winter foals (born in February to early March), a group of researchers wondered if that metabolic reduction could affect fetal development.

The researchers, led by Christine Aurich, DVM, PhD, Dipl. ECAR, of the University of Veterinary Medicine Vienna, and Elisabeth Beythien, Tierarzt (a veterinarian from a German university) of the Graf Lehndorff-Institute for Equine Science, studied 27 broodmares and their foals. All the mares had similar diets and a similar number of previous foalings. Gestation length and the sex ratio of foals did not differ.

The mare–foal pairs were grouped by foaling date: Group 1 foals were born between February and early March; Group 2 between early March and early April; and Group 3 from mid-April to May.

The researchers measured the size and weight of each mare’s placenta at birth. The measurements were smaller in the winter-foaling mares than mares delivering later. This indicates a reduction in nutrient transfer to the fetus, which could influence fetal growth.

A number of size parameters were also recorded for each foal weekly from birth to 12 weeks of age. Researchers found that most parameters—including height at withers, distance from fetlock to carpal joint and length from poll to nose—were lower in the earliest foaling group compared to the other groups. Foal weight did not differ among the groups.

“The size difference of the early-born foals was present over the whole observation period, i.e., until 12 weeks of age,” says Dr. Beythien. After that time, the mares and foals were sent out to pasture and could not be easily measured.

Despite the initial size disparity, Dr. Beythien notes that early-born foals will be taller and larger than later-born foals during the first few months of life simply due to the difference in age. “If you imagine a foal presentation scheduled in June, foals born in March will be taller than foals born in May because they are approximately eight weeks older at this time,” she explains.

For this reason, breeders often feel early-born foals have an advantage in young-horse competitions at 3 to 4 years of age. Ultimately, though, breeding mares too early in the year could be detrimental to the foals’ mature size, says Dr. Beythien. Based on other studies, she adds, the lower energy supplied to the winter foals during gestation may also contribute to health problems during adult life. Therefore, the team concluded, breeders may be better off aiming for foals to be born during the natural foaling season (typically between April and September) when they’ll “experience a healthier environment during gestation,” says Dr. Beythien.

This article was originally published in the November 2017 issue of Practical Horseman. 

Osteochondrosis dissecans is a developmental disease that can affect the bones in a horse’s joints as well as related cartilage. Essentially, OCD occurs when the cartilage at the end of long bones doesn’t develop properly. The disease can cause bone fragments in the joints, fissures (cracks) and bone cysts—all giving the horse pain and potentially lameness and performance issues. Multiple factors can contribute to the development of OCD, including genetics, bone growth rates, endocrine levels, exercise and diet.

Since OCD is a developmental disease, meaning it’s seen in growing foals, understanding potential risk factors that occur during the early months of a horse’s life is important. A team of researchers based at the University of Liege in Belgium and the country’s Equine Research and Development Center of Mont-le-Soie wanted to learn more about how a foal’s diet during that time frame might affect the development of OCD. Led by Luis Mendoz, DVM, they focused specifically on whether foals were fed a high-energy diet based on concentrates (grain) or a diet based only on forage.

The team monitored a group of 204 foals, starting at 6 months (after weaning) and followed them for a year until they turned 18 months. They took X-rays to look for signs of OCD at both age points. Based on their findings, the researchers were able to fit the foals into four categories:

•  No OCD lesions at either 6 or 18 months (132 foals)

•  Lesions at both 6 and 18 months (37 foals)

•  Lesions at 6 months that healed by the 18-month exam (19 foals)

•  No lesions at 6 months but developed lesions by 18 months (16 foals).

Researchers compared these groups with nutritional details gathered from questionnaires on each foal. They found that foals who had no signs of OCD at 6 months but who were then fed concentrates were more likely to develop lesions. On the other hand, foals who already showed OCD lesions at 6 months of age and then ate only grass, hay or other roughage with no concentrates in their diets, showed a high probability of recovering from those lesions by the time they reached 18 months.

The team concluded that a foal’s diet can influence the progression of OCD and that, in particular, a high-energy diet can increase the risk of this disease. In the bigger picture, this supports a more general theory that management practices play a crucial role in the likelihood that a foal will develop OCD. 

This article was originally published in the June 2017 issue of Practical Horseman. 

If you breed your mare this spring, will her foal be a filly or a colt? The answer may depend partly on her age and the age of the stallion that you choose, research from Brazil suggests. Veterinarians at Pontifical Catholic University Minas in Betim analyzed breeding records in two groups of horses and found similar patterns in both.

One group comprised nearly 60,000 Mangalarga Marchador horses born in Brazil from 1990 to 2011—basically all the males registered in those years and an equal number of randomly selected females. The researchers sorted the horses according to the ages of their parents at the time of conception, which ranged from 3 to 25 years. Then they calculated the sex ratio of the offspring by parental age. They found:

• The odds of a female foal increased along with the age of the mare or stallion, and the trend was more marked for aging mares than for the stallions. Mares aged 10 to 15 were less likely to have colts than were mares aged 5 to 10, and mares 15 to 20 even less likely.

• A big gap in age between the stallion and the mare also seemed to be a factor. Older stallions were more likely to sire colts when they were bred to younger mares. Older mares were most likely to give birth to fillies when bred to younger stallions.

The second group was made up of 253 horses of various breeds born into a herd from 1989 to 2010. They were the offspring of 16 stallions and 119 different mares. In this smaller group, mares older than 15 also had more fillies than the younger mares. But the stallion’s age had no significant effect on the sex of the offspring. 

The researchers concluded that parental age affects the sex ratio among foals and that this effect is stronger for mares than for stallions. If your heart is set on having a colt from your mare, then your best shot is to breed her while she’s young. —Elaine Pascoe

This article originally appeared in the January 2016 issue of Practical Horseman.

A thoroughbred event horse ties up after a distance workout. A Welsh Pony suffers a crippling episode of laminitis. A young warmblood in training for dressage develops sore hocks. Different horses, different breeds, different circumstances and different problems, but in each case, heredity may be partly to blame for the trouble. 

Genes, the coded instructions within body cells, control how every living creature appears and how it functions. Genes help determine whether a horse excels as an athlete or falls prey to certain diseases. Now scientists are deciphering the genetic code, and their work could lead to major breakthroughs in horse health. Researchers are investigating the role of genes in diseases ranging from moon blindness in Appaloosas to melanomas in gray horses. 

Here, Molly McCue, DVM, MS, PhD, an associate professor at the University of Minnesota College of Veterinary Medicine and a leading researcher in the field of equine genetics, explains what’s being learned about the role of genes in five conditions that are common in sporthorse breeds and that affect muscle, metabolism and bone. Your horse’s genes won’t necessarily dictate his destiny, she says, but knowing about them may help you take better care of him.

Breeds, Genes and Health 

Modern horse breeds are nothing like the wild horses of prehistory. Over centuries, selective breeding has concentrated genes that influence performance traits like strength and speed, as well as conformation and color. But as breeders have focused on desirable traits, they’ve inadvertently concentrated some genes that may increase a horse’s risk of disease or unsoundness. 

Science is just beginning to untangle these links. Aided by computers, Dr. McCue and other researchers are able to quickly read (or sequence) large numbers of DNA samples. They are using that ability to locate disease-related genes with a technique called genome-wide association. 

The method involves analyzing DNA from hundreds or thousands of horses, some diagnosed with the condition being investigated and some unaffected. The researchers hunt for genetic markers, DNA sequences with known locations. Markers near a disease gene are shared much more frequently by affected horses than by unaffected horses, and those markers are used to map the location of disease genes. Once the researchers know which small area of a chromosome has a disease gene, they can select specific genes to sequence to find the exact variations that are responsible.

“There are simple genetic traits, like gray coat color. If a horse has the gray mutation, he will gray with age,” Dr. McCue says. In these cases whether a horse has a certain gene determines whether he develops the corresponding condition. Hyperkalemic periodic paralysis, a disorder that affects certain Quarter Horses, is an example. HYPP affects the complicated chemical/electrical events involved in muscle contraction. Horses that have it can suffer uncontrolled muscle contractions, weakness and even paralysis or respiratory failure. It has been traced to a single genetic mutation passed on by Impressive, a leading Quarter Horse sire with many descendants, and horses that trace to Impressive can be screened for the defective gene. Those that have it will develop HYPP, although the condition varies in severity and can often be managed with changes in diet and exercise.

For most breed-related conditions, though, the picture is more complex. “More than one gene may be involved, and the influence of the environment is important,” Dr. McCue says. That’s the case with the disorders covered here.

Muscle Trouble

Muscle stiffness and spasms, sweating, rapid breathing and reluctance to move are signs of tying up, which can cause damage to muscle. Horses with the muscle disorder known as polysaccharide storage myopathy (PSSM, also called equine polysaccharide storage myopathy or EPSM) may tie up after even light work. 

What happens: Muscles need energy to work and they keep a supply in the form of glycogen, a complex sugar they break down when need arises. In PSSM excess glycogen builds up in muscle fibers. Some of the excess is stored in the form of an abnormal complex sugar, a key feature of the disease that can be discovered with a muscle biopsy. The condition is like a metabolic monkey wrench, interfering with the ability of the muscle to function. 

Diet and management have a big role in this condition. Most PSSM horses stop showing signs when they’re switched to high-fat and -fiber, low-starch rations, but they still remain susceptible.

Who’s at risk: PSSM occurs mostly in Quarter Horses and related breeds, draft breeds and crosses and warmbloods. It seems to be slightly different in different breeds:

• Quarter Horses typically have classic signs of tying up.

• Draft horses often show muscle weakness and atrophy or have difficulty backing and picking up hind feet. 

• Warmbloods often develop sore muscles and may show reluctance to collect.

The types of work these horses do may partly account for the signs, but it appears that different genetic factors are involved.

What’s known: Researchers have identified a genetic mutation that causes one form of the condition, PSSM Type 1. The mutation is dominant, meaning that a horse who gets a copy of the gene from either parent can develop the condition. A test for the gene is available through the University of Minnesota Veterinary Diagnostic Laboratory.

However, not all horses with the condition have this mutation. “We think that about 20 percent of Quarter Horses with PSSM as diagnosed by muscle biopsy have a different form, Type 2,” says Dr. McCue. “We think that about 80 percent of warmbloods with PSSM based on muscle biopsy have something other than Type 1. We call that Type 2, but whether it is the same as what the Quarter Horses have, we don’t yet know.” 

What’s next: Dr. McCue’s lab has been hunting for a PSSM Type 2 gene. “We think we have identified the region where it exists, but we don’t have the gene yet,” she says. More forms of the disease may surface, she adds. “There are many glycogen-storage muscle disorders in other species—including more than a dozen in humans—so it’s possible that horses get more of these disorders than have been identified so far.” 

More Muscle Trouble

Any horse may tie up if he’s exercised harder than his level of conditioning allows—when his workload is abruptly increased, for example, or he returns to work after time off. This form of tying up is called exertional rhabdomyolysis, and some horses are more susceptible. Horses that tie up repeatedly are said to have recurrent exertional rhabdomyolysis. 

What happens: RER often appears as horses move up in training. Typically these horses tie up with sustained exercise (for example, a distance workout at a moderate pace). Some research suggests RER involves a problem with the way calcium, which plays a vital role in muscle contraction, is regulated inside the muscle cells. 

Who’s at risk: While any horse can suffer an incident of tying up in the right conditions, Thoroughbreds, Standardbreds, racing Quarter Horses and Arabians are the breeds most often affected by RER. The condition has been reported in 5 to 7 percent of Thoroughbreds and Standardbreds. 

What’s known: Researchers at the University of Minnesota have been studying RER in Thoroughbreds and Standardbreds. “They show similar signs, but the precise mechanisms may be different,” Dr. McCue says. The condition seems to be moderately heritable in both breeds. “A good portion of the risk is genetic, but other factors determine whether the individual develops the problem,” she says. Besides work level, triggers include a nervous temperament and stressful conditions. Fillies are more likely than colts to develop the disorder. Diet—especially large amounts of grain or sweet feed—also seems to be a factor. Signs often improve with changes in exercise, diet and management.

What’s next: Researchers are working to identify the genetic risks for tying up. They hope to locate the gene or genes that result in altered muscle contraction, along with other genetic factors that may affect muscle development and function.

Susceptibility to tying up is not a simple genetic trait, Dr. McCue notes. “This truly is a complex genetic disease. The causes are environmental and genetic combined—if you manipulate the environment, you affect the outcome. These complex genetic conditions are where research is heading.“

Shivers

Shivers is a neuromuscular disease in which muscles in the hindquarters undergo periodic spasms.

What happens: Signs often appear when a handler tries to back the horse. The muscles in the pelvis and thigh may tense or tremble, and the horse may hold a hind leg flexed and trembling. He may jerk his tail upward or hold it aloft. The signs are intermittent, so it can be hard to diagnose. The cause is unknown. 

Who’s at risk: Shivers mainly affects draft breeds but has also been reported in warmbloods, warmblood-crosses and some light breeds. 

What’s known: A genetic connection seems likely—shivers has been seen for centuries, and old reports suggest that careful breeding could prevent it. So far no specific genetic pattern has been identified, though, and there is no genetic test.

Because some breeds are prone to both shivers and PSSM, the two conditions were once thought to share common genetic roots. But a University of Minnesota study of Belgian draft horses found no direct relationship between PSSM and shivers, Dr. McCue says, so the association is probably a coincidence. 

What’s next: “We need a better understanding of shivers before we can find a genetic cause,” Dr. McCue says. Difficulties in finding cases and accurately diagnosing the disease complicate the work. As a starting point, researchers have studied videos of horses with reported shivers in an effort to better define its characteristics. Dr. Stephanie Valberg, of the University of Minnesota’s Neuromuscular Diagnostic Laboratory, and Dr. John Baird, of the Ontario Veterinary College, are among the scientists involved in this effort.

Metabolic Syndrome

Three features characterize equine metabolic syndrome: 

• Insulin resistance, a metabolic problem that makes it hard for a horse to process carbohydrates 

• Obesity (or regional fat deposits, like a cresty neck)

• High risk of laminitis, a devastating foot disorder in which the bond between the hoof wall and the underlying bone weakens or gives way. 

EMS shares those signs with equine Cushing’s disease (pituitary pars intermedia dysfunction), a different condition that mainly affects horses over age 15, but EMS appears at a younger age.

What happens: Digestion breaks down carbohydrates in grain and forage into glucose, a simple sugar, that is absorbed into the horse’s bloodstream. The rising blood-sugar level signals his body to produce insulin, a hormone that allows body cells to take in glucose and convert it to energy. In insulin resistance the cells don’t use insulin properly, so the horse must produce more insulin to move glucose into cells. The problem is similar to Type 2 diabetes in humans (except that horses don’t typically develop high blood glucose as diabetics do). A horse with insulin resistance needs a special diet with limited starch and sugar to avoid overwhelming his system and triggering an attack of laminitis.

Who’s at risk: EMS is common in Welsh and other ponies, Morgans, Arabians, Andalusians and a few other breeds. It occurs less often in Thoroughbreds and Quarter Horses. Within the breeds, some horses seem more susceptible.

What’s known: “Great efforts are being made to understand EMS,” Dr. McCue says. Environment plays a big role in this disorder. If a horse is overfed and overweight, for example, he’s much more likely to develop signs. But, Dr. McCue says, “It’s not just that horses are fed too much—there are clearly underlying genetic factors.” When horses are managed under the same conditions, some develop the disorder and some don’t, she notes, and a chubby horse with EMS can lose weight but still have the metabolic problem. 

Dr. McCue’s research team has gathered data on 600 EMS horses of various breeds, comparing glucose and insulin blood levels, body fat and other variables. The results are awaiting publication. Meanwhile, the researchers are hunting for genetic factors that may make horses susceptible to EMS. Dr. McCue suspects that multiple genetic factors contribute. Some are probably important across breeds, while others may be important only in some breeds. There may be genetic factors that protect horses against the condition, too.

What’s next: “We are looking first within the Morgan breed to find out what genetic factors affect the condition in those horses,” Dr. McCue says. Her team has identified key regions of the genome and is looking for specific variations, or alleles, associated with EMS. The team has also collected samples from 300 Welsh Ponies and plans to do the same with them. 

“Being able to identify these alleles will allow us to assess risks in horses of different breeds,” Dr. McCue says. For example, it may be that Welsh Ponies are prone to EMS if they have a certain allele that affects fat metabolism, while different alleles may be more important in Morgans. Also, she says, “The effects of different alleles may add up to determine the risk for an individual horse. A horse may have only one or two of these alleles and so be at less risk than an individual who has more of them.” 

Joint Defects

Osteochondrosis involves defects in the way bones develop at joints. The defects can appear in any of the leg joints, but the hock, stifle and shoulder are common sites. Although the defects typically form in the first year of life, signs often don’t appear until the horse begins training. Then, as he puts extra loads on his bones and joints, he comes up lame. 

What happens: In young horses, growth cartilage at the joints gradually mineralizes, hardening into bone and leaving just a thin cartilage layer at the working surfaces of the joint. In osteochondrosis the process is incomplete. The cartilage may thicken and tear, a bit of cartilage or bone may pull away, or a fluid-filled pocket (a subchondral bone cyst) may develop in the bone under the cartilage. 

Who’s at risk: Standardbreds, warmbloods, Thoroughbreds, Quarter Horses, Paints and European drafts have the greatest risk. Osteochondrosis is also more common in certain bloodlines within breeds. 

What’s known: Many factors—nutrition, growth rate, exercise levels, conformation, injury—affect osteochondrosis. Genes are clearly involved, but it’s unlikely that the risk will be traced to a single gene. Instead, Dr. McCue says, the genetic picture may be similar to that of EMS—various alleles, some more important in certain breeds and bloodlines than others, interacting in ways that compound risks. 

Ongoing studies in the United States and Europe are looking at the genetic risks for osteochondrosis in different breeds and different joint surfaces. University of Minnesota researchers have been concentrating on hock osteochondrosis in American Standardbreds. “We’ve found some likely genetic loci and identified some potential mutations that may be associated with the disease,” Dr. McCue says. Annette McCoy, DVM, PhD, spearheaded the Standardbred research at Minnesota and will continue her work in her current post at the University of Illinois.

What’s next: “The next step will be to test our findings in an independent population of European Standardbreds, to see if the association is still present,” Dr. McCue says. “We also hope to bring together the many research projects on osteochondrosis in a wider collaboration.” If the researchers can come up with a set of specific genetic variations that contributes to the disease, they’ll be able to apply the findings to assess the risk faced by any individual horse. 

Long-Range Goals 

The goal of genetic research isn’t to condemn horses that carry genes linked to health problems, Dr. McCue says. Instead, genetic information provides information on risks. 

“Armed with that information, you can make smart decisions and manage horses better to reduce the risk,” she says. “If a foal is at risk for osteochondrosis, you can adjust his nutrition and grow him slowly to limit the risk. If a horse is at risk for EMS, you can monitor his diet and take him off pasture in spring. If a mare has an allele for a complex genetic disease, that doesn’t necessarily mean you can’t breed her. It just affects your choice of a mate; you breed to a horse that doesn’t share the same risk factor.

“This is where we’re headed with this research—finding a way to improve horses’ welfare,” she says. “We hope the horse-owning public will embrace this goal and not be fearful of the outcomes.”

Sidebar: Eight Things to Know About Your Horse’s Genes

1. Your horse has about 20,000 genes, arranged in 32 chromosomes inside the nucleus of nearly every cell in his body. 

2. The chromosomes are basically long molecules of DNA (deoxyribonucleic acid). DNA molecules form twisting, paired strands, a pattern often referred to as a double helix. They are made up of chemical units called nucleotide bases, which act as a sort of genetic alphabet.

3. Each gene is a segment of DNA. The order of the nucleotide bases in the gene provides a set of coded instructions for making specific proteins that are used to build body tissues and carry out body functions. 

4. A horse gets one copy of each chromosome from his sire and one from his dam, so he has two copies of every gene. The copies will be found in the same place (locus) on the paired chromosomes.

5. Sometimes a “spelling error” occurs in the code, resulting in a variation, called a mutation.

6. Minor differences in the code produce variant versions, or alleles, of genes. Variations can affect visible traits like coat color, but more often their effects aren’t so easy to spot. 

7. If a foal gets different alleles of a gene from his sire and dam, he’s heterozygous for that gene. If both alleles are the same, he’s homozygous for that gene. 

8. When a horse is heterozygous for a given gene, one of the two alleles will control the gene’s function. That allele is dominant and the other is recessive. Gray coat color is an example of a trait controlled by a dominant allele.

This article originally appeared in the March 2015 issue of Practical Horseman.