LEXINGTON, Ky. – While testing continues, the latest results indicate cyanide or cyanogenic compounds as the likely culprit in the death for hundreds of Kentucky foals in recent weeks.
Wild black cherry trees are likely the source of these compounds with Eastern tent caterpillars directly or indirectly involved in the delivery to horses.
Researchers caution that the current observation is preliminary.
University of Kentucky agronomist Jimmy Henning said there is an extremely close association between the presence of wild cherry trees, the presence of Eastern tent caterpillars in very high numbers and both early foal loss and late term abortions.
Tests show that white clover was not the source of cyanide on problem farms. Also, ergot alkaloids from bluegrass or orchardgrass were not the cause, nor were fescue toxicosis or mycotoxins a likely cause,
Eastern tent caterpillars tested May 4, were negative for cyanide, but retrospective inquiries indicate these caterpillars had not eaten cherry tree leaves or any plant material for more than six hours.
A sample of preserved Eastern tent caterpillars taken April 20, is strongly positive for cyanide.
Wilted black cherry leaves are known to be toxic to cattle and sheep. Wilting leaves substantially increases the content and availability of cyanide. These same leaves are a favorite food of the Eastern tent caterpillar and this spring black cherry trees where stripped of their leaves by a large infestation of the caterpillars.
Early results of tissue analysis from late term foals suggest cyanide, said Thomas Tobin, professor at the UK Maxwell H. Gluck Equine Research Center. Cyanide causes death due to lack of oxygen in tissue and triggers a strong “gasp” reflex. Necropsy results were not inconsistent with death due to cyanide, he said.