A research project has determined that it probably isn’t a virus or bacteria (a biological agent) that links the Eastern tent caterpillar (ETC) to mare reproductive loss syndrome (MRLS). Bill Bernard, DVM, Dipl. ACVIM, an internal medicine specialist at Rood and Riddle Equine Hospital in Lexington, Ky., and Manu Sebastian, DVM, MS, a pathologist with the University of Kentucky’s Livestock Disease Diagnostic Center (LDDC), conducted the experiment in late May/early June. This project was funded by KTOB, creating what researchers are calling the “triad” approach–university, private practice, and industry involvement–to solving this problem.

The experiment showed that irradiated Eastern tent caterpillars can induce fetal loss in late-term pregnant mares. This suggests MRLS is caused by a non-infectious agent in caterpillars (irradiation at sufficient levels has been shown to kill infectious agents such as viruses and bacteria). The study was the first experiment to reproduce pathological findings similar to naturally occurring late-term MRLS.

“The big question people wanted answered was is it a biologic agent or a chemical?” noted Bernard. “Most people think it’s something in the caterpillar, whether it’s something they leave on the grass or something in the caterpillar itself is unknown.”

After gathering caterpillars from Kentucky (the numbers were much smaller this year than in the past two years), those caterpillars were irradiated and given to mares to see if it caused abortion. Three out of six mares did abort. “That suggests that it is a chemical,”