05/23/2001 12:00AM

Cherry trees latest suspects


LEXINGTON, Ky. - First mycotoxins in the grass, then caterpillars, and now researchers are wondering if cherry trees may have contributed to the syndrome that has caused at least 1,200 early- and late-term abortions in broodmares in central Kentucky.

As theories abound, the bottom line on Wednesday remained the same: No one has identified a cause for the mare reproductive loss syndrome.

A release issued Tuesday evening by the Gluck Research Center said the scientists are now focusing on Eastern tent caterpillars and the chief component of their diet, the wild cherry tree, whose leaves are toxic to horses.

On Wednesday, scientists and veterinarians were considering a pair of cherry tree-related theories. One proposed that caterpillars digested prussic acid from the leaves and converted it to cyanide, which they excreted on grass, where pregnant mares ate it. Another theory suggested that cherry seedlings had sprouted in pastures, and mares ate them.

"Visual correlations on several farms that have experienced MRLS show the presence of wild cherry trees in or near fields where affected mares were grazing, but we still do not know if there is a one-to-one correlation between the presence of wild cherry trees and incidences of MRLS," the Gluck release said. "Since [Eastern tent caterpillars'] primary host tree is the wild cherry, a very in-depth look is now underway to determine if and how ETCs or wild cherry trees have roles in the cause of MRLS."

But the theories have some holes, most notably that caterpillars and their excrement first tested earlier this month proved negative for cyanide.

Caterpillars tested positive for the mycotoxin zearalenone, initially a leading suspect in the syndrome. But most pasture samples scientists collected tested negative for mycotoxins - another contradiction that sent researchers back to caterpillars and cherry trees.

Veterinarians first began to notice the syndrome, which caused abortions in mares close to foaling and early fetal losses in mares 60 days past conception, on April 26. From April 28 through noon on Tuesday, Lexington's Livestock Disease Diagnostic Center had received 529 stillborn or aborted foals thought to be affected by the syndrome. The early fetal losses, estimated at 678 on May 8, were thought to have reached well beyond 1,000, though researchers have not released more recent statistics on those abortions.

Lexington had an unusual infestation of the tent caterpillars in April, immediately before the wave of abortions. Millions of caterpillars emerged from their large, bag-like nests and denuded their host fruit trees in mid-April, then moved into the surrounding environment. Farm managers throughout Lexington reported that they had found the caterpillars in pastures, barns, and water troughs--leading them to suspect that mares may have been ingesting either the caterpillars or their fluids.

So far, Gluck center researcherswho have led investigations into the fetal losses-haven't said whether they agree with that scenario. But, in reviewing their old publications, they have found records of caterpillar infestations around the same time as fetal losses in 1980 and 1981. Another similarity: temperature fluctuations in March and April. This year, central Kentucky had unusually cold temperatures in March, followed by above-average highs in the 80's in April, a pair of freezes on April 17 and 18, and a late-April return to high temperatures - a pattern similar to the springs of 1980 and 1981.

Gluck researchers never conclusively identified the cause of the early fetal losses 20 years ago, and many Lexington horsemen doubt they will find the cause this time, now that the caterpillars have become moths and several days of heavy rain have washed away potential pasture problems.

"If it was either one of those problems, it should be getting better," said Taylor Made Farm manager Frank Taylor. "Things are starting to look better out here. We've had 22 live foals in a row now, and today we checked 20 mares and all but one was still in foal."