“We can prevent mare reproductive loss syndrome (MRLS) as we experienced in 2001 and 2002 by keeping horses away from caterpillars,” said Bruce Webb, PhD, a University of Kentucky (UK) researcher who has been studying the condition that terminated thousands of mare pregnancies in Central Kentucky and nearby states. The pervading theme at a Nov. 30, 2005, meeting at Keeneland in Lexington, Ky., was that more needs to be understood before researchers can effectively intervene in the MRLS disease process.

The scientists presented 14 months of Kentucky Thoroughbred Owners and Breeders (KTOB) Foundation-sponsored research material and suggested future study avenues. Topics included:

Eastern Tent Caterpillars (ETC)–Researchers suspect that small lesions created in the mare’s gastrointestinal (GI) tract by the caterpillars’ setae (hairs) might allow bacteria to enter and circulate in the body to somehow reach the fetus and ultimately cause abortion. UK’s Karen McDowell, PhD, David Horohov, MS, PhD, and Neil Williams, DVM, PhD, used skin tests and histologic sampling to find that setae did not modify the mare’s immune response.

Webb said to keep pregnant mares off pastures with caterpillars for eight weeks after trees lining the pastures are sprayed with a caterpillar insecticide. Also, introducing a caterpillar virus early in the ETC season could dramatically decrease ETC numbers