Research in the past five years concluded the stiff hairs on Eastern tent caterpillars consumed by pregnant mares pierce the horses’ digestive tracts, possibly allowing bacteria to enter the bloodstream. The bacteria can then attack the placenta and spread to the fetus. MRLS can cause late-term foal losses, early-term fetal losses, and weak foals. Fetal death from infection by these alimentary tract bacteria is the hallmark of MRLS.

“This year, before we saw the first case of MRLS, entomology researchers at UK predicted an increase in caterpillar numbers this spring,” said Neil Williams, DVM, PhD, Dipl. ACVP (see extension report www.ca.uky.edu/news/?c=n&d=328). “With our ability to predict increases in caterpillars and diagnose abortions, we at the university try to help the industry by putting out information to alert horsemen.”

This spring, seven of the cases were late-term foal losses and six were early fetal losses, according to Williams. Of the 13 cases, seven were Thoroughbreds. Other breeds, which included one case each, were American Saddlebred, Standardbred, Rocky Mountain, Oldenburg, Gotland, and one mixed breed fetus. The numbers of cases by county were: Woodford County, four; Scott and Jessamine Counties, two apiece; and Bourbon, Boyle, Fayette, Oldham, and Rockcastle Counties, one apiece