Cyanide poisoning linked to the possible consumption of Eastern tent caterpillars stands as the latest leading theory on Mare Reproductive Loss Syndrome, a mysterious ailment that has shocked the horse-breeding capital of the world, just 85 miles south of Cincinnati. It was so hard to come in here and lose two, three or four foals a day. Scientists at the University of Kentucky's Gluck Equine Research Center have been racing to figure out what's killing the foals. They've checked for viruses, bacteria, even toxic molds that might have been growing on pasture grass. Eastern Tent Caterpillars prefer eating Black Cherry leaves, which have a naturally high concentration of cyanide, a poison that can concentrate in the caterpillar.
Initial tests reveal that the caterpillars can contain enough cyanide to kill four or five mice.
An unusual weather pattern, involving a late April freeze, may have forced the caterpillar to migrate from trees hurt by the weather during the breeding season. While migrating, pregnant mares may have consumed the caterpillars, from eating them with pasture grass or drinking some as they congregated on water troughs. The cyanide may have harmed pregnancies by poisoning early fetuses, and by playing havoc with the placenta in late-term pregnancies, forcing premature births. But now, they're focusing on a common backyard pest. The syndrome has affected all types of horses from high-priced thoroughbreds in Kentucky to common breeds raised on small farms in Ohio, West Virginia and other states.