02/05/2002 12:00AM

MRLS a mystery, meeting affirms

Email

LEXINGTON, Ky. - With breeding season set to start within two weeks, University of Kentucky researchers are still studying a range of possible causes of last spring's mare reproductive loss syndrome.

The scientists acknowledged at an informational session Monday night in Lexington that they had yet to identify the disease's cause, and their initial theory - that Eastern tent caterpillars and wild cherry trees were the leading suspects - is now just one of many possibilities under investigation.

MRLS, the name given to the thousands of mysterious late- and early-term abortions in mares last spring, also may be related to other syndromes seen last spring in horses of all ages and both genders: pericarditis (swelling of the heart sac), epicarditis (swelling of the surface musculature of the heart), and unilateral uveitis (an eye problem that caused about 40 horses to go blind in one eye).

The session started hours after Clemson University researchers announced results of a study showing a correlation between the presence of poison hemlock plants and the occurrence of MRLS. The Clemson study followed one by UK that identified a high correlation between caterpillars, cherry trees, and MRLS.

But UK entomologist Dr. Lee Townsend, who did not participate in UK's panel presentation last May when the caterpillar theory was first announced, told a crowd of nearly 400 farm managers and breeders that caterpillars, who feed on cyanide-producing wild cherry trees, were unlikely to be direct carriers of cyanide to horses; Townsend presented research by UK's Dr. Bruce Webb showing that cyanide essentially disappears from the caterpillar during digestion.

But Townsend did not dismiss another theory that became public this fall: that droppings, or grass, left in pastures by last April's massive infestation of caterpillars provided an excellent growth medium for fungi, which then may have caused MRLS.

In any event, the researchers recommended that farm owners use pesticides to eliminate the tent caterpillars this spring when their nests are baseball- to softball-sized.

Identifying what, if any, pasture-related toxins might have caused or contributed to the syndrome is a complicated task, as Dr. Kyle Newman of Venture Laboratories in Lexington pointed out.

Newman noted that while scientists have identified about 1,000 mycotoxins that are toxic to animals, there are probably thousands more to be discovered, each operating in a different way and possibly changing according to circumstances and environment.

If mycotoxins are to blame for MRLS, Newman said, it's possible that there's more than one at work. "We may have something of a mutt here, a mixture combining several kinds of mycotoxins," Newman said.

Roger Allman, a pasture specialist from The Farm Clinic, said that his monthly sampling revealed nothing out of the ordinary with regard to mineral content. But he did recommend that pastures be mowed to a height of five to six inches, as studies indicated some correlation between mowing of fields and MRLS occurrence.

Discussing clinical signs of MRLS, veterinarian Stuart Brown of Hagyard Davidson McGee noted that bacteria found in about 70 percent of the aborted fetuses also might provide an important clue for researchers.

But for now the cause remains elusive.

"Simple experiments have not proven fruitful," UK agronomist Jimmy Henning acknowledged in opening the meeting.

Communication needs upgrading

A major theme at the MRLS discussion was communication. The breeding community has criticized the university and its Gluck Equine Research Center for being slow to discuss its work and findings to breeders on the front line fighting MRLS.

Henning announced that, in addition to an oversight committee including representatives from the research and breeding worlds, UK has established an informational list serve on the Internet. Horsemen can register for that at the UK website at www.ca.uky.edu; they also can communicate with the researchers via e-mail at mrlsinfo@uky.edu and by phone at (859) 257-MARE.

Henning also said that scientists will monitor 12 central Kentucky farms, including one hay farm, and will work to distribute any alerts through the UK website and list serve, the media, and an Equine Industry Task Force managed by Kentucky Thoroughbred Association executive director David Switzer.