Caterpillars, cherry trees may take blame for foal deaths in Kentucky

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Scientists now believe that cyanide related to cherry trees and eastern tent caterpillars may have caused the deaths of at least hundreds of foals in Kentucky.

Meanwhile, the instances of early fetal loss, late-term abortions, and the births of stillborn and weakened foals appear to be declining on Kentucky horse farms. As of May 23, the University of Kentucky's Livestock Disease Diagnostic Center had received 532 dead fetuses and foals for examination. A total of 508 were brought in between April 28 and May 19; however, they received only 24 since.

The team of researchers investigating the cause of the mysterious mare reproductive loss syndrome, including private veterinarians and faculty of the University of Kentucky's Gluck Equine Research Center, originally focused on mycotoxins in pastures as the main cause of the problem. But test results on pasture samples collected in May have been negative for mycotoxins.

The new predominant theory is that cyanide naturally occurring in cherry trees affected the mares, causing the reproductive problems. Scientists aren't yet sure how that could have happened, but said that eastern tent caterpillars, which prefer to make their home in wild cherry trees, may have had a role.

Initial inspections revealed that most of the farms hardest hit by the foal loss did have cherry trees, although an exact correlation has not been established. Heavy infestations of eastern tent caterpillars were reported in the springs of 2000 and 2001, when the affected mares had been bred.

"We want to emphasize that the current observations are preliminary, must be confirmed, and that further validation is absolutely essential," said Scott Smith, dean and director of the University of Kentucky College of Agriculture. "We have not yet met reasonable standards of scientific proof of the working hypothesis. A great deal of work remains to be done."

For more information, including updated statistics from the Livestock Disease Diagnostic Center, check the mare reproductive loss syndrome Web site at