Florida Farm & Feed

Cherry Tree Theory

Natural Cyanide May Be Killing Foals

From the Associated Press

(May 25, 2001)

LEXINGTON, Ky. (AP)
- The theory hasn’t been confirmed, and it isn’t clear how the poison got into the pregnant mares, but observations implicate cyanide as the cause of more than 500 foal deaths and aborted fetuses, University of Kentucky College of Agriculture Dean Scott Smith told breeders and farmers Thursday night.

This spring’s large infestation of Eastern tent caterpillars, which feed on cheery tree leaves, may have played a role in transferring the poison, scientists said.

“We have to conclude the wild cherry-caterpillar complex is the lead suspect” in the deaths, said Dr. Jimmy Henning, a University of Kentucky agronomy professor.

One theory is that the mares ingested the caterpillars’ fecal matter, which contained the cyanide, said Thomas Tobin, a professor at the University of Kentucky Gluck Equine Research.

Scientists have been scrambling to find answers to explain why foals have been dying and mares have been losing fetuses at a staggering rate this spring. The mystery has sent fear through the state’s $1.2 billion thoroughbred industry, which produces about a third of the nation’s foals each year.

Clues Hard to Come By

Tests have failed to support other hypotheses about the outbreak, Henning said. Blood samples showed no evidence of infectious or contagious diseases, and early samples from pasture grasses provided no clues.

The deaths haven’t been uniform across the region either. Some farms haven’t reported any unusual stillbirths or miscarriages, while others have reported miscarriage rates of 10 percent to 75 percent.

A similar unsolved outbreak occurred in 1981, a year with weather similar to this year’s, with a warm, dry spring followed by several hard freezes and subsequent dry weather.

“It replicates in mirror image the month of April back in 1981, when history relates a very similar syndrome,” said David Powell, equine epidemiologist for the Gluck research center.

Number of Deaths Slows

The number of deaths is slowing this week, with only 24 since Sunday, said Dr. Bill Bernard, internal medicine specialist at Rood and Riddle Equine Hospital. “It’s near the end of the breeding season, so there’s fewer mares left to foal, but it’s still encouraging,” he said.

Whatever the cause, researchers are confident that the worst is over.

“If the cherry trees are the cause, that’s the best possible explanation for the future,” Smith said. “In many ways now, we can predict what to look for and ways to prevent it.”

David Switzer, executive director of the Kentucky Thoroughbred Association, said farmers still have hopes of salvaging this foaling season, which runs through June.

“We’ll keep proceeding forward and look for whatever the cause of this is,” Switzer said. “Once we do that, we’ll all march right into 2002 with all the confidence in the world that this is not going to return.”             ¶