In late April, veterinarians doing sonograms to sex 60-day-old fetuses in central Kentucky discovered that an unusual number of them were dead. Soon, farm managers were taking aborted and stillborn foals to the University of Kentucky's Livestock Disease Diagnostic Center in Lexington daily, while sick foals with respiratory problems, inflamed eyes, and fluid buildup around the heart were showing up at veterinary clinics. Scientists from around the United States and abroad mobilized to find out the mystery ailment striking the heart of the thoroughbred industry.
Infectious agents were ruled out, as were toxins from fungi growing on feed grasses and fescue. Eastern tent caterpillars were also suspected; some were found to have high levels of cyanide and a fungal toxin called zearalenone. Another clue was that foal deaths often seemed to happen in areas with many cherry trees.
That's when it all came together. Cherry tree leaves were dry this spring after a freak hot weather spell in March followed by a freeze and then a drought. Under such conditions, the leaves produce large amounts of cyanide, says toxicologist Thomas Tobin of the university's Gluck Equine Research Center. Caterpillars, extremely abundant this spring, favor these trees and had stripped most of them bare by the end of April, he says. When the cyanide-laden critters and their equally toxic feces dropped into pastures and water tanks, they were eaten by pregnant mares, scientists believe. The mares were fine, but high levels of cyanide were found in aborted fetuses. The toxin blocks oxygen delivery, which explains the foals' respiratory difficulties and other symptoms, Tobin says.
Although no more foals have died recently, a team of experts is now visiting central Kentucky stud farms to figure out exactly how the calamity occurred--and to prevent it from happening again.
University of Kentucky Web site about the syndrome
Keeneland's homepage, with a video of the meeting