Another MRLS theory suggested

Another MRLS theory suggested

Dec 01, 2001
By staff

Lexington, Ky.-A new "hybrid" theory has recently surfaced suggesting a blend of caterpillars, molds, and the right timing during gestation might have caused the springtime late-term abortions and early fetal losses, called the mare reproductive loss syndrome (MRLS), according to The Horse Interactive.

Dr. Bruce Webb, an entomologist at the University of Kentucky, believes "frass" is the missing link to the MRLS puzzle.

He says the contributions of "frass," the technical term for caterpillar excrement, a mixture of urine and feces, comprise the trigger factors for the losses.

Caterpillars feed on wild cherry tree leaves containing levels of cyanide; an earlier theory suggests horses reacted to cyanide found in the frass.

"The way I look at this is that you need to look at every link in the chain," Webb says. "When I start looking at the cyanide hypothesis - there's no doubt that there's cyanide in the leaves. The caterpillars eat those leaves, but cyanide is detoxified in the foregut of the caterpillar.

Webb says the original theory "didn't really fit" what was known about insect physiology.

But what Webb and Dr. Kyle Newman, a nutritional microbiologist of Venture Laboratories, discovered was that mycotoxins, previously suspected as MRLS culprits, might be involved in the caterpillar theory. Scientists have said mycotoxins are released by molds under stressful climatic conditions like the hard freeze that hit in April.

Webb and Newman have shown that frass supports the growth of molds which may produce mycotoxins known to cause reproductive problems, and are collecting caterpillar egg masses to hatch in the laboratory this winter.

Dr. Thomas Riddle of Rood and Riddle Equine Hospital says he thinks the mold/fungal theory "make a lot of sense."

"I'm definitely leaning toward that now. No one knows for sure what the cause was, but to me, that is the best way that has been proposed to fit all the syndromes together- the eyes, the heart, the abortions, foal deaths."