Veterinarians interested in reproduction and perinatology (the foal immediately after birth) crowded into the Reproduction/Perinatology Forum at the 2003 American Association of Equine Practitioners' convention to discuss mare reproductive loss syndrome (MRLS), terminology for the mare breeding soundness examination, vaccination of broodmares with the West Nile virus vaccine, current trends for applied reproductive techniques, and today’s educational opportunities for students interested in equine reproduction. The forum was facilitated by Stuart Brown, DVM, a practitioner at Hagyard-Davidson-McGee Veterinary Hospital in Lexington, Ky., and Steven Brinsko, DVM, MS, PhD, Dipl. ACT, of Texas A&M University.

Update on MRLS
Mare reproductive loss syndrome hit Kentucky and surrounding states hard in 2001, causing abortions of early- and late-term foals, along with cases of pericarditis and uveitis. Brown said that cases were down significantly in 2002, and were reduced even more in 2003. In 2003, there were no cases of uveitis (eye inflammation) and pericarditis (inflammation of the pericardium, the sac that surrounds the heart) reported in connection to MRLS, according to Brown.

The focus on the cause of MRLS has been on the Eastern tent caterpillar (ETC) as more studies have showed that ETC can cause abortions if fed to horses. Feeding trials have narrowed the cause down to the exoskeleton (skin) of the caterpillar. Using the pig as an experimental model, three out of five pregnant gilts (female pigs) that were fed ETC aborted. Upon further inspection, microgranulomas (small, localized areas of inflammation only visible under a microscope) containing caterpillar setae (hair) were found inside the digestive tract of some of the gilts that were fed ETC, while the control group did not have microgranulomas. For more on this study and others, see our Mare Reproductive Loss Syndrome topic page.

The reduction in the incidence of MRLS in 2002 and 2003 was expected since the natural biological cycle of ETC should have resulted in fewer caterpillars after such a boom in the population in 2001. In addition, horse breeders in Kentucky have used elimination methods, such as approved pesticides, removal of host cherry trees, and removal of caterpillar tents.

Brown said researchers might want to find ways to radiolabel ETC setae to track their route through the GI tract and circulatory system of mares. Studies will continue to narrow down the exact cause of MRLS, and researchers will continue to search for why and how bacteria entered affected fetuses.

Terminology for the Mare Breeding Soundness Exam
Brown asked attendees if the terms defined by the American Association of Equine Practitioners (AAEP) were current enough. During a discussion about the definition of “suitable for breeding” and “pregnant mare,” attendees dissected the various parts of the definitions to see if the wording should be modified or if anything should be added. It was decided the terminology should be further reviewed by a designated task force of the AAEP.

West Nile Virus Vaccine and Pregnant Mares
Due to a 2003 article in The Denver Post saying mares were aborting their foals and foals were being born with congenital defects due to the West Nile virus vaccine (see West Nile Virus Vaccine: Adverse Effects in Mares?), a discussion was opened up about experiences of attendees with the vaccine and broodmares. One Kentucky researcher commented about how easy it is for misinformation to spread across the Internet. In this instance, none of the supposedly affected foals were examined to find the cause of abortion, and quotes taken from veterinarians at Fort Dodge Animal Health, manufacturers of the vaccine, were misconstrued by The Denver Post, she said. "We can't believe everything we read," she said. "Always consider the source."

One veterinarian pointed out that a mare can abort from just about anything. He said that he has not seen a trend of mares aborting after vaccination with the WNV vaccine, and he would still recommend vaccination of pregnant mares. Veterinarians from Florida, Texas, Colorado, and other states agreed.

One Colorado veterinarian commented that, unfortunately, the article in The Denver Post came out at the same time that the virus hit the state. He said that it took diligence to educate clients about the vaccine.

Brown pointed out that the vaccine is very efficacious, while another veterinarian pointed out that very few vaccines are actually labeled for use in pregnant mare. Despite this, veterinarians have been vaccinating pregnant mares for years without major adverse side effects.

The discussion turned to recommended WNV vaccination schedules. In Florida and Texas, it has been recommended that horses be vaccinated every four months due to the year-round mosquito population. As for vaccinating foals, some recommended vaccination at six weeks of age, with two boosters a month apart following the initial series, while others were unsure of when it is safest to vaccinate foals. Research currently being conducted at the University of California, Davis, should shed further light on this issue.

Applied Reproductive Techniques
Attendees discussed current trends in applied reproductive techniques, particularly embryo transfer. One veterinarian said that there seems to be a discrimination by buyers against foals produced from embryo transfer at Standardbred sales. He was surprised to note that sale catalogues at these sales denote embryo transfer foals. He said people seem to think that these foals will not be as athletic.

Veterinarians familiar with the Quarter Horse industry mentioned that perhaps embryo transfer foals are not considered as valuable since there is another similar offspring of the same year on the market. However, since Standardbred breeders are only allowed to register one foal from one mare per year, then the value of the embryo transfer foal would not be reduced since there is only one. The question was brought up as to whether breed registries were stamping these foals as less desirable through requirements to denote embryo transfer foals in sales catalogues.

Education of Veterinary Students
Veterinary student attendees were asked their opinion of their education and whether they were given enough experience in veterinary school in the area of reproduction. All who offered their opinions agreed that more experience is always better. Students at Texas A&M and the University of Florida discussed how they are able to opt for a two-week equine theriogenology rotation to practice palpations and other reproductive exams. In contrast, the University of Missouri offers a two-week theriogenology rotation with all species covered. Students commented that with some procedures, such as embryo recovery, they might only do it one time while in veterinary school, so they face a lot of uncertainty after graduation.

One veterinarian commented how important it was for veterinarians to mentor students and to show them what a wonderful lifestyle veterinarians have. He brought up the point that some students will shy away from large animal medicine in favor of an increased starting salary in small animal practice. However, he said it was important for students to know that within five to seven years after graduation, large animal veterinarians will make more money than their small animal counterparts.

It was suggested that the AAEP begin a mentoring program that would pair up experienced veterinarians with students for improved education.

About the Author

Sarah Evers Conrad

Sarah Evers Conrad has a bachelor’s of arts in journalism and equine science from Western Kentucky University. As a lifelong horse lover and equestrian, Conrad started her career at The Horse: Your Guide to Equine Health Care magazine. She has also worked for the United States Equestrian Federation as the managing editor of Equestrian magazine and director of e-communications and served as content manager/travel writer for a Caribbean travel agency. When she isn’t freelancing, Conrad spends her free time enjoying her family, reading, practicing photography, traveling, crocheting, and being around animals in her Lexington, Kentucky, home.

Stay on top of the most recent Horse Health news with FREE weekly newsletters from Learn More