By Murray Evans
The Associated Press

LEXINGTON - At this time in 2001, equine doctor Bill Bernard had seen almost 50 horses affected by a mystery disease that caused the loss of thousands of foals. This year, he's seen no cases of Mare Reproductive Loss Syndrome.

As researchers have learned more about the disease, preventing it has become easier. Most researchers believe the culprit is the eastern tent caterpillar. There's still some debate about whether it's the caterpillar itself or a biological agent inside the caterpillar, but Bernard said the massive outbreak of Mare Reproductive Loss Syndrome in Kentucky in 2001 coincided with a large infestation of the caterpillars.

"The good news is we think it's the caterpillar and we can do something about it," said Bernard, an internal medicine specialist at Rood and Riddle Equine Hospital in Lexington.

In late April 2001, pregnant mares began developing weak foals, which needed days of medical treatment to survive, if they lived at all. During the following weeks, hundreds of foals died and thousands of mares lost early-term pregnancies as a result of the illness. By the time the deaths subsided, about 3.8 percent of the state's foal crop and 15 percent of the foals that would have been born in Kentucky that year had been lost.

Eastern tent caterpillars like to make their homes on cherry trees, where they feed on the trees' cyanide-laced leaves. The caterpillars also will reside on apple, crab apple, purple-leaf plum, ornamental pear and oak trees. Bernard said the trees can be treated to repel or kill the caterpillars and pregnant mares can be kept away from the caterpillars.

"The first year we had MRLS, 20 to 30 percent of the mares were affected," he said. "Last year we were down to 5 percent. This year, the caterpillar control is so good, it is minute."

The effects of the 2001 outbreak will be felt economically for years, said Jim Williams, director of communications for Keeneland Race Course.

Keeneland's prestigious July Selected Yearling Sale, an industry staple since 1944, will not be held in 2003 because of the disease's effects.

Eighty-seven horses were bought at last year's sale at a total price of $42.385 million.