MRLS Workshop

Since the devastating disease process known as mare reproductive loss syndrome (MRLS) appeared on the scene in 2001 (and reappeared in 2002), concerted efforts have been focused on understanding and controlling the problem. Economic losses to the horse breeding industry have been staggering. On Aug. 27-28, the principal players--in both the scientific and applied aspects of MRLS--and a number of noted reproduction specialists from across North America convened at a workshop in Lexington, Ky.

The group undertook a detailed review of the investigative efforts that have been focused on this crisis during the past 18 months, then tried to plot a course for the future. In two full days at the University of Kentucky's Maxwell H. Gluck Equine Research Center, the 100 or so presenters and participants reviewed the clinical, diagnostic, and causal aspects of MRLS, considered the many research efforts underway, and tried to evaluate control measures that have been developed. Then the group rolled up its collective sleeves to plan future efforts against MRLS.

The concept for this gathering came from the Gluck Center's David Powell, BVSc, and Tom Tobin, MVB, MSc, PhD, MRCVS, DABT.

Initial presentations from veterinarians concerned the clinical manifestations of early fetal loss, late-term abortion, pericarditis (heart), and uveitis (eye) cases.

Next was information on the diagnostic aspects of MRLS. The Kentucky Livestock Disease Diagnostic Center has necropsied and evaluated many of the MRLS cases from Central Kentucky. The significant pathological findings were presented, including some of the unusual aspects of these losses. For example, bacteriological examinations yielded organisms not usually correlated with pregnancy loss.

Environmental, climatic, and other epidemiological factors were explored. In-depth surveys of farms with and without problems were used to identify risk factors. There were clear associations of Eastern tent caterpillars (ETC) and black cherry trees with MRLS. Evaluating weather factors showed that similar sudden temperature variations just prior to both the 2001 and 2002 outbreaks did occur. Neighboring states, primarily Ohio, had similar problems.

Discussions of the toxic factors that might contribute to pregnancy loss were delivered, and a study attempting to show specific changes associated with ETC in lab mice was presented. That work was inconclusive, but it opened doors for future investigation.

Other possible factors that are known causes of fetal loss, such as ergot-infected fescue, cyanide, mycotoxins, and estrogens, were mentioned as possible contributors to MRLS. In the course of the meeting, all of these were dismissed as principal causes of the signs noted in MRLS.

Several trials attempting to prove the role of ETC in early and late pregnancy loss were reviewed. Abortions occurred in mares in early and late pregnancy in the studies. While these findings lend credence to the association with ETC, concern was expressed as to the similarity of these administrations to natural exposure.

There was a set of presentations about ETC biology, behavior, and distribution. Control systems used by breeding farms and potential other means of attracting the insects to remove them from the environment were described. Key information about ETC was provided by Terry Fitzgerald, PhD, a recognized expert in this area.

In the final session of the workshop, Keith Betteridge, BVSc, MSc, PhD, FRCVS, led a discussion of where we now stand in the quest for answers, and what direction researchers should take. There followed a spirited discussion, with ideas put forth and questions raised. Should we search for small animal models of these diseases to facilitate less expensive research? What about the bacteria isolated from these cases; are they really part of the pathogenesis, or just incidental findings? If bacteria are involved in the process of terminating the fetus, how do they gain access? Do they invade through the cervix as an ascending infection, or get in via the bloodstream? What part of the caterpillar is involved in the disruption of the pregnancy? What is the chemical nature of the toxin associated with the caterpillar, or is it even a toxin that's involved?

A final tally revealed the majority accepted the ETC as critical in the cause of MRLS, but there was discussion about that, as well! The meeting ended with all involved vowing to continue this quest.

About the Author

A.C. Asbury, DVM

A. C. (Woody) Asbury received his DVM from Michigan State University in 1956, then spent 21 years in California in breeding farm practice and at UC Davis. He joined the faculty at the University of Florida in 1977 and was involved in teaching, research, and administration until 1996. An Emeritus Professor at Florida, he lives in Kentucky, where he and his wife are developing a small farm.

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

Free Newsletters

Sign up for the latest in:

From our partners