These unexplained deaths of first trimester and third trimester unborn foals are unprecedented in the history of horse raising anywhere in the world. Last week several experts thought the answer was mycotoxins - poisonous residues left by fungi and molds on grasses. Scientists thought that the combination of very hot weather in the first two weeks of April followed by two days of freezing temperatures stressed the grasses so much that the parasitic molds and fungi took over and concentrated toxins that the horses ate. But this week laboratory results were negative for mycotoxins. So now the focus has shifted to the lowly Eastern Tent caterpillars and the wild black cherry trees they live upon each spring.
Tent caterpillars make silken tents to live in while they feed on their host trees.
These collective nests are homes to the caterpillars from 4 to 6 weeks before the cocoon and moth stages. Photograph courtesy University of Kentucky College of Agriculture. There were so many caterpillars in Kentucky this year that whole cherry trees on farms were stripped bare. Wild cherry trees are known to have cyanide in their leaves. If the trees are stressed while protecting themselves from wildly fluctuating temperatures as occurred in April, the leaves will produce even more cyanide.