06/07/2001 11:00PM

Foal losses slow; research goes on


LEXINGTON, Ky. - The mare reproductive loss syndrome that recently struck central Kentucky's broodmares, causing at least 1,200 early fetal or near-term abortions, appears to have abated. But researchers' work hasn't slowed.

While University of Kentucky researchers survey farms, a federal laboratory in Utah is preparing to conduct tests on fetal tissue and mares' blood samples.

A statement issued Friday by UK said, "Detailed investigations are under way to prove or disprove the possibility of cyanide as the cause of MRLS. In addition, the investigation of other possible causes including mycotoxins, fungal endophytes, phytoestrogens, chemical compounds and infectious agents is still under way, although results to date provide no evidence that they are involved in the cause of MRLS."

As of June 8, UK had received about 130 surveys from Thoroughbred, Standardbred, American Saddlebred, and Morgan farms.

UK researchers also met Wednesday with veterinarians to discuss whether recent cases of pericarditis - swelling of the sac around the heart - and eye problems are related to the syndrome.

"Approximately 50 cases of each condition have been identified to date involving a wide age range of horses and breeds," the statement said. "These cases are not necessarily associated with mares that have experienced early or late fetal losses. Twelve necropsy cases of pericarditis have been examined at the Livestock Disease Diagnostic Center."

UK researchers have theorized that mares ingested cyanide originating in nearby cherry trees, possibly after an infestation of Eastern tent caterpillars, which eat cherry trees, exposed pastures to the toxin in their droppings. Last week, Dr. Dee Cross, a Clemson University professor hired by several major Thoroughbred farms, proffered a different theory: that mares grazed on poison hemlock plants, which are toxic to many species and are a recognized cause of birth defects in cattle, sheep, swine, and goats.

The University of Illinois already has found evidence of low levels of cyanide, or a compound containing cyanide, in "a small set of selected tissue samples" UK researchers sent for testing, according to Dr. Lenn Harrison of Lexington's Livestock Disease Diagnostic Laboratory. Now, the United States Department of Agriculture's Poisonous Plant Research Laboratory in Logan, Utah, will test samples for hemlock's toxic alkaloids.

The earlier cyanide positives "make a strong case for cyanide," said PPRL research toxicologist Dr. Kip Panter, who is coordinating the alkaloid testing. "But if we find hemlock alkaloid in the fetal tissue samples and in the mares' blood and urine, that will be a strong indication that would jump hemlock up on the list a good bit."

Panter said that the most likely place to find hemlock toxin is in fetal liver and kidney tissue, which will be screened for all of the alkaloids hemlock produces. "We'll test the mares' serum samples first, and if we don't find anything there - and these alkaloids can leave the animal very quickly - we will move on to the fetal tissue," he said. "The chances of finding it are much greater there in fetal tissue, because it recirculates in amniotic."

Testing is expected to take about three days.

Cherry-related poisoning in horses is relatively well-known. But, even though its effects are well-documented in cattle, sheep, goats, and swine, there are few studies regarding the effects of poison hemlock in horses. That may change someday: Panter said that in recent years PPRL researchers have been interested in conducting a study of the plant's effects on pregnant mares, because of the reproductive problems it causes in other mammals.

"There is a lot of anecdotal information, but not much has been published," said Panter, who has studied hemlock poisoning in other species and has witnessed horses eating the plant if there is little other choice forage.

Panter acknowledges researchers may never identify a definite cause. "This case is so unusual, you wonder if there weren't multiple factors," he said. "I think what it boils down to at this point is eliminating pieces. Maybe we can eliminate poison hemlock as a cause, and maybe we can eliminate cyanide, but we'll always wonder what it was."

That means wondering about prevention, too. As research into the cause continues, some breeders are operating in uncharted territory in an effort to protect their mares.