02/04/2002 1:00AM

Report puts hemlock back on suspect list

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LEXINGTON, Ky. - Nine months after mare reproductive loss syndrome first was discovered in a wave of fetal loss among Kentucky broodmares, researchers are still working to identify the cause of the disease.

Now, a Clemson University team has released results of an epidemiological study that appears to support one of many theories about the disease's cause.

Clemson researchers Dr. Dee Cross and Sam Gray, who worked with statistical analyst Dr. Billy Bridges, said Monday that their study of 38 pastures on 11 central Kentucky farms affected by the syndrome yielded a high correlation between the presence of poison hemlock that showed evidence of consumption by horses and the occurrence of MRLS. The study was funded by Clemson, The Grayson-Jockey Club Foundation, Purina, Bayer, and Equi-Tox, a company established by Cross to research fescue toxicosis in mares.

"Our statistics showed that there is a less than 1 in 10,000 chance that poison hemlock was not related to the problem," Cross said. "That's a very high relationship in pastures that showed evidence that the horses had consumed hemlock."

But that statistic alone isn't definitive proof that hemlock caused or contributed to an estimated 5,000 abortions in Kentucky's broodmares. A larger study of 133 farms by University of Kentucky researchers last year showed a high correlation between MRLS and the presence of wild black cherry trees and eastern caterpillars, which UK put forward last June as likely suspects in the MRLS outbreak.

Do the two studies contradict each other? Not necessarily, considering that cherry trees and poison hemlock plants often appear in the same areas, in pasture enclosures and fence lines that aren't easily mowed.

That leaves room for more research, and scientists continue to test a range of MRLS theories, including fungus-produced pasture toxins, caterpillars, unbalanced phosphorus and nitrogen levels, and others.

Since presenting its initial theory - that caterpillars were a mechanism in carrying naturally occurring cyanide from cherry trees to mares - UK hasn't yet announced successful duplication of the disease in the lab, a key step in determining MRLS's cause.

That's the next challenge for Cross and Gray, who have proposed a new study of the effects of hemlock ingestion in 14 pregnant mares. They tried a similar study in just two mares last year, using frozen samples of hemlock they collected from affected Kentucky pastures last spring, but they discovered that after four months in frozen storage, the samples had lost 75 percent of their toxicity. The mares didn't abort, either because the frozen hemlock was no longer highly toxic or because hemlock simply doesn't cause abortion in mares. The inconclusiveness encouraged the men to plan their 14-mare study with fresher plants.

Cross and Gray began investigating the abortions, at several farms' request, last May 10, less than a week after breeders began widely reporting early fetal losses and a higher rate of late-term abortions. Based on their observations at nearly a dozen central Kentucky nurseries that sustained losses, Cross and Gray theorized that some mares grazed on poisonous young hemlock plants when an unseasonable April freeze damaged or killed their preferred forage.

But the hemlock theory lost some currency in the public mind after tests on the aborted fetal material failed to show evidence of hemlock's signature alkaloids. At the time, the United States Department of Agriculture official who conducted those tests, Dr. Kip Panter, noted that hemlock's telltale organic compounds could be fleeting, lasting no more than 50 hours, which could render tests useless.

For breeders, such seemingly contradictory information makes preventive planning difficult. UK has distributed suggested steps to cut down exposure to caterpillars and cherry trees, and Cross, too, has some advice.

"We're guarded in our conclusions so far, and we want to go on to the next phase of research," he said. "But if it is hemlock, then there's some good news. Hemlock is very easy to control with herbicide."

Monarchos Claiborne deal finalized

Owner John Oxley announced Monday that he has finalized a deal to send 2001 Kentucky Derby winner Monarchos to stud at Claiborne Farm in Paris, Ky. The 4-year-old Maria's Mon colt will stand his first season for a $25,000 fee.

Claiborne's Gus Koch said that Monarchos, who retired Jan. 28 after injuring a tendon in his left front ankle, is expected to arrive at the farm on Thursday. The colt currently is with trainer John Ward in Florida.

Oxley said Monday that he would retain "a substantial interest" in Monarchos; Claiborne owner Seth Hancock has said that Oxley would retain 50 percent of the horse and syndicate the remaining interest.