MRLS outbreak in Washington raises new scientific questions - DVM
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MRLS outbreak in Washington raises new scientific questions


"Another thing that I have noticed that would correlate well with MRLS in Kentucky, is that this year we've come up with an inordinate number of mares that were checked in-foal, but have come up open. That is something that we don't see very often, we've had quite a number of them compared to other years."

From those mares that aborted in 2003, and from the diagnostics, Feigner did not see echogenic material or evidence of similar infection to those foals noted as ill in Kentucky. "I did not see any of that, or such similarity. From the few samples submitted, the WSU Diagnostic Lab essentially came up with "nothing," which I understand is pretty typical of MRLS."

Caterpillars everywhere"On a lot of these farms in Kitsap County, caterpillars were floating within the water troughs," says Feigner. "Even when I suspected that there was something going on (in relation to the caterpillars), I had these mares muzzled so they would not ingest the insects as they drank, that didn't seem to make a difference. They could leach out into the water, but what happened was hard to determine or to know."

Last year this infestation was so uniquely located in Kitsap County, that those people that bred their mares there and took there mares back home where they didn't have the problem, their mares had their babies normally.

It's a potential I guess, says Dr. Bud Hallowell, DVM, equine reproductive specialist, "but I haven't heard of anyone around here (Auburn) having any problems, any mares aborting this year."

"A former client of mine did have a few abortions last winter, at about 9 months or so, though they seemed to be random and unrelated, as much as we could tell.

Though she thought it wasn't MRLS, she did come up with an interesting observation. Some of those affected here in Washington were mares that were previously affected with MRLS in Kentucky, and had lost foals the previous year. Those affected were found in different fields, and it was curious that some of them were mares that were previously affected with MRLS, even though some of them had not gone back to Kentucky and were therefore not exposed to that environment.

She thought it might be a residual affect from the previous exposure and resultant MRLS that might be lingering. It was total speculation that they might be related to their previous bout of MRLS."

Worm in the ointmentBack in the Bluegrass that fateful May, the University of Kentucky initiated a strategic plan within the entire equine industry- veterinarians, horse farm managers and scientists from several disciplines were brought together to determine what had plundered Thoroughbred and other horse farms throughout the region. Since that time with dedication and determination, this stalwart group made incredible progress.

During the past three-year investigation several potential suspects were called into question including the possible pasture toxins - Fusarium mycotoxins, zearalenone mycotoxin, ergot and loline alkaloids in the general pasture foliage and in tall fescue specifically, phytoestrogens and cyanide in white clover, nitrates in representative forage samples, poison Hemlock and cyanide from the black cherry tree leaves. Even ethylene glycol dropped from airliners flying overhead and emptying their bathrooms was considered.

Enemy # 1The true culprit was not found in the growth of the pastures, but turned out to be a small invader to the trees surrounding them. The Eastern Tent Caterpillar became known to be horse enemy #1 in relation to MRLS.

The first inkling of the involvement of the caterpillars was their heavy infestation, where astride many of the pastures was the wild back cherry tree, the ETC's primary host tree.

Looking back at the calendar, it was noted that the caterpillars had stripped the trees by April 25th . This contamination date correlated well with the first episodes of fetal loss.


Source: DVM360 MAGAZINE,
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