Since the beginning of the mare reproductive loss syndrome (MRLS) in 2001, there have been many theories as to the cause of the problems. Honing in on the extreme number of Eastern tent caterpillars (ETC) in 2001 and 2002, studies have shown that early fetal loss can be caused by feeding ETC to pregnant mares. It also has been shown that freezing the caterpillars does not destroy whatever toxin or organism (virus or bacteria) is causing problems, since frozen ETC have been used experimentally. The abortogenic cause associated with ETC also isn’t only found in Kentucky, since ETC from Michigan were used in one study.

Bill Bernard, DVM, Dipl. ACVIM, of Rood and Riddle Equine Hospital in Lexington, Ky., who with Michelle LeBlanc, DVM, Dipl. ACT, conducted a study on caterpillars and frass (excrement) earlier this year, did a pilot study to try and determine if it was the intestinal contents of the caterpillar or the integument (external portion) of the caterpillar that was associated with early fetal loss. The results indicated that it is something external on the caterpillar that is associated with abortion, not something in the caterpillar’s gastrointestinal tract. He hopes to continue this research in a double-blinded study in the spring.