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 Mare Reproductive Loss Syndrome
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December 9, 2005

Research Updates


A series of scientific presentations on recent research studies into MRLS were given at the Keeneland Sales Pavilion, Lexington on Wednesday November 30, 2005. The research updates were given under the auspices of the Kentucky Thoroughbred Owners and Breeders (KTOB) Foundation which since 2004 has provided significant financial support for these projects.

The first was by Dr. Karen McDowell from the Maxwell H. Gluck Equine Research Center and Dr. Neil Williams from the Livestock Disease Diagnostic Center of the University of Kentucky College of Agriculture who described an investigation to study whether the setae or hairs of the Eastern Tent Caterpillar (ETC) exerted an effect on the immune response of the mare following exposure to MRLS. Administering various treatments of ETC setae alone or combined with poke weed mitogen as an immune stimulant, via intradermal injection into the mare’s skin, it was determined that setae did not alter the local immune response.

Dr. Bruce Webb from the Department of Entomology, University of Kentucky College of Agriculture described findings from three different studies he and his colleagues had undertaken. The possible role of the mouse as an alternative animal in which to study MRLS was evaluated but proved not to be successful. A field study was initiated by the question as to how long pregnant mares should be kept off ETC contaminated pastures during the spring. Observations concluded ETC cadavers persisted on pasture for a period of 7-8 weeks.

A third study demonstrated that ETC infection with an insect baculovirus is a factor in controlling the population dynamics of the caterpillar from year to year. The study suggested that ETC baculoviruses were the primary agent causing a decline in ETC in Central Kentucky over the last two years. By artificially infecting caterpillar nests each season with virus grown in the laboratory it may be possible to exercise biological control, suppressing growth of the ETC population.

Dr. Kyle Newman of Venture Laboratories, Lexington described investigations he and colleagues are currently undertaking on bacteria isolated from tissues and fluids derived from fetal losses attributable to MRLS. He emphasized that the bacteria referred to as MRLS-like Streptococci and Actinobacilli have not been isolated from caterpillars and are not prominent flora of the reproductive tract of mares. MRLS-like Streptococci (the majority of which are closely related to Streptococcus criceti) are found in the alimentary tract of mares with a greater concentration in the upper part of the tract, the tongue, tonsillar area and esophagus. These studies are ongoing but initial results suggest that fetal and oral isolates are similar but unique to the individual mares. Comparing isolates from different mares demonstrates differences suggesting the source of fetal and placental infection in each mare is derived from its own bacterial population.

Dr. Donald Schlafer from the College of Veterinary Medicine, Cornell University described a surgical procedure for catheterization of the fetus allowing blood samples and various measurements to be performed on the fetus in utero. The technique would allow continuous monitoring of the fetus within the uterus of the pregnant mare.

The final presentation was a review by Dr. McDowell of the significant milestones and findings which have been identified during the investigations into MRLS since its appearance in Kentucky during the spring of 2001.


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