Updated on 09/15/2011 12:16PM

If not mycotoxins, what?

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LEXINGTON, Ky. - Some central Kentucky grass samples have tested negative for mycotoxins, leading a prominent equine nutritionist to question the theory that toxins produced by fungus are responsible for the deaths of at least 1,200 late-term foals and early-term fetuses in the past month.

Dr. Steve Jackson, a nutritionist whose clients include some of central Kentucky's major farms, said Tuesday that a variety of pasture samples he had tested by Trilogy Laboratories in Missouri have proven negative for any mycotoxins.

The cause of the deaths, which have been called mare reproductive loss syndrome, has not yet been identified. Researchers at the University of Kentucky's Gluck Center, which has taken the lead role in examining the problem, have said they strongly suspect fungus-infected grass that mares have eaten.

Jackson said that testing at a Nebraska laboratory may have produced false positives for mycotoxins in some grass samples.

According to Jackson, many grass samples that he collected before May 5 - just as farm managers and veterinarians were becoming aware of the syndrome - were sent to Midwest Laboratories in Nebraska, where some tested positive for zearalenone, a mycotoxin that is known to cause reproductive difficulties in other species. Jackson sent a different set of samples, after May 5, to Trilogy Laboratories, which tested negative for mycotoxins.

"The Nebraska laboratory uses ELISA [enzyme-linked immunosorbent assay] techniques, which are not as specific as the HPLC [high-pressure liquid chromatography] technique used in Missouri," Jackson said.

Jackson said the next step will be to send residual material from Nebraska to Missouri and have the zearalenone-positive material tested again under the HPLC techniques.

"If they come back negative, then we'll know we had false positives."

But if mycotoxins aren't the problem, what is?

"Everybody, in their own area of expertise, is continuing to thrash this thing from every angle," Jackson said. "It has got to be something the horses were exposed to in the pasture. There's no way around that. It's highly linked to exposure to pasture, and the losses have been greatest among mares exposed to pasture for the greatest number of hours."

Local horsemen have been suspicious that the major infestation of tent caterpillars in April may be related to the syndrome, and the Gluck Center reported earlier this week that some caterpillars have tested positive for zearalenone.

"The fit of the caterpillar is pretty good," Jackson said, "but I can't figure out how to get the caterpillar in the horse."

From April 28 through noon Tuesday, the University of Kentucky's Livestock Disease Diagnostic Center reported that it received 529 aborted or stillborn foals or late-term fetuses for evaluation. In addition to those losses, farm managers have reported hundreds of mares losing early-term pregnancies at about 60 days after conception. The most recent figures available for early fetal loss, presented by the Gluck Center on May 10, put the number at 678 as of May 8. But the number has grown since then, according to anecdotal reports from central Kentucky farms.

The Gluck Center announced Monday that it has scheduled a second informational meeting for horsemen at Keeneland's sale pavilion on Thursday at 5 p.m.

Gluck researchers will update the investigation, and veterinarians and farm managers will give give briefings. A 30-minute question-and-answer session will follow. The meeting will be broadcast over the Internet at www.keeneland.com.

* Thoroughbred Charities of America has agreed to make an emergency donation of $25,000 to the Gluck center for its research into the abortion problem.