[Mike]

I heard Paul Harvey talking about this a year or two ago, hope its
not too old to post:
http://www.rgs.uky.edu/ca/odyssey/spring02/foaldeaths.html

On Kentucky Derby Saturday, May 5, 2001, 73 dead foals and fetuses
were delivered to the Livestock Disease Diagnostic Center at UK’s
Coldstream Research Campus on Newtown Pike. And while weekend
deliveries of dead animals to the back door of the center is common,
the tremendous number that day—about 10 times more than usual—was
alarming.

“I knew we had big trouble on our hands. In addition to these foals
and fetuses, we were aware that too many foals in the Fayette County
area were being born weak,” says Lenn Harrison, veterinarian and
center director. Harrison worked alongside center pathologists
practically non-stop that weekend—the first of many—to try to solve
the puzzle of what was causing the death of so many foals and
fetuses.

In the lab, pathologists performed a necropsy on each foal, looking
at internal organs for signs of infection as well as taking blood
and tissue samples for analysis. The tissue samples offered up the
clue of rare bacterial infections in many aborted fetuses, but the
pathologists concluded that these bacteria could not be solely
responsible for the deaths. “As the necropsies continued, our belief
got stronger that the bacteria were secondary to the specific cause
of what was dubbed Mare Reproductive Loss Syndrome,” Harrison says.

Within the next two days, the total number of dead foals and fetuses
brought to the center grew to 276, and a team of over 100 experts
from a variety of disciplines in the College of Agriculture joined
the investigation. A group of highly experienced veterinarians made
up a survey to be distributed right away to horse farms by the
Kentucky Thoroughbred Farm Managers Club to try to determine the
extent of the losses. Staff in the UK agricultural communications
office also swung into action to make certain that the industry and
the public were kept abreast of the situation. And a Web site,
http://www.uky.edu/Agriculture/VetScience/mrls, was established to provide
a continuing source of information for the public.

By May 10, news of the syndrome had spread around the world: U.S.
networks as well as European and Middle East news agencies were
constantly calling UK for information about this syndrome that had
the potential to disrupt the global horse industry. Four days later,
May 14, farm managers who had returned questionnaires confirmed the
worst: the syndrome was widespread, and it was continuing.

“At this point, a couple of faculty members at Gluck [UK’s Gluck
Equine Research Center] recalled that in 1980 and 1981 early fetal
loss had occurred spontaneously and no cause had ever been
determined,” Harrison says. “And in both years the losses abruptly
stopped.” Reported losses during those years, however, were nowhere
near the 2001 numbers.

“A quick check of meteorological conditions then and now,” he
explains, “showed a disturbing similarity of weather patterns that
could affect pastures where the mares grazed.” March temperatures
all three years were below normal, followed by above normal
temperatures in April. Such a pattern would result in explosive
biological activity in both plants and insects. The data also showed
frost or freeze in the third week of April, followed by warm
temperatures a few days later. What impact could those factors have
on the pastures?

“Although the convergence of weather factors in the three years with
larger than usual abortion rates wasn’t a smoking gun, it was
suggestive that something weather-related was responsible,” Harrison
says.

Perhaps, he thought, weather-dependent vegetation could be linked to
a variety of possible disease-causing agents, including mycotoxins
and ergot-type alkaloids (which are derived from fungi and can be
poisonous to animals in high concentrations) and phytoestrogens
(compounds produced by plants that mimic the hormone estrogen).
Tests for poisoning from mycotoxins in feed, ergot-type alkaloids in
pasture, and phytoestrogens appeared to be negative, but most of the
tests were done after the syndrome had occurred.

Because none of the obvious causes appeared plausible, the
scientists turned their attention to still another possibility—that
the villain might be the Eastern tent caterpillar, whose populations
were high in each of the years in question. Harrison showed UK
agronomist Jimmy Henning some information he’d run across on these
prolific crawlers, in particular the fact that they feed on wild
cherry leaves.

Although the caterpillar-cyanide theory hasn’t held up in recent lab
tests, the Eastern tent caterpillar’s role in the foal deaths is
still being investigated. [photos by Steve Patton]

And when Henning visited farms where mares had given birth to dead
or dying foals or had aborted early-term fetuses, he discovered a
striking pattern: most of the pastures had a large number of wild
cherry trees. “I knew that cherry tree leaves carried the precursor
to a poison—naturally occurring organic cyanide—that could cause
death in horses and other animals, especially cattle,” says
Henning. “I also realized that Eastern tent caterpillars, which were
known to feed on the leaves of cherry trees and were seemingly
immune to the poison, had been quite active during late April.”

The caterpillars became even stronger suspects in a meeting of
veterinarians, farm managers and the media on May 24. “At that
meeting,” Harrison says, “several veterinarians confirmed that the
incidence of early fetal losses as well as stillborn and dying foals
had dramatically decreased during the previous week, paralleling the
natural decline in caterpillar numbers.”

The investigation into the possible role played by the caterpillars
continued. In December 2001, entomology professor Bruce Webb made an
interesting discovery: his research showed that cyanide does not
accumulate in the caterpillars, so they are not likely to deliver
appreciable amounts to horses. This finding does not mean, however,
that the caterpillars were necessarily innocent bystanders. Research
planned by Webb this spring will investigate potential indirect
roles that the caterpillars may play. “They produce large amounts of
waste as they feed,” Webb explains. “Much of this nutrient-rich
material rains to the ground under infested trees and may serve as
food for specific molds that produce toxins that might contribute to
the syndrome.”

As researchers close in on the causes of the foal-loss syndrome, the
importance of their work is underscored by last spring’s sad
numbers. Between April 28 and May 12, 418 aborted equine fetuses and
stillborn foals were brought to the Livestock Disease Diagnostic
Center for evaluation. During that same period in 2000, only 60
fetuses and stillborn foals were received. On May 23, 2001, a
University of Kentucky survey of 159 thoroughbred farm managers
indicated that 678, or 21 percent, of 3,294 pregnant mares had
experienced early fetal loss.

So, what can be done now and in the future to make certain that such
an aberration doesn’t occur again?

Henning says that researchers have begun a complex environmental
monitoring system they hope will give them advanced warning if
conditions are ripe for this to happen again. About 13 farms are
being tested on a rotating basis, with soil, grass, water and other
samples collected, analyzed, and stored for later comparison should
foals again begin to die in such numbers. Weather patterns are also
being closely tracked, and a massive research initiative on the
causal mechanisms of the syndrome is planned by the College of
Agriculture in the coming months.

Harrison says he hopes that the only thoroughbred problem he will
have to deal with around Kentucky Derby time this year is which
horse to bet on.

Jeff Worley