|College of Agriculture|
June 26, 2003
Researchers Get Closer to Solving Caterpillar Mystery
LEXINGTON, Ky., (June 25, 2003) – Last year several studies produced
solid evidence that the presence of Eastern Tent Caterpillars is strongly associated
with the foal loss problem known as Mare Reproductive Loss Syndrome. But precisely
how the caterpillars were causing mares to lose their pregnancies was unknown.
Research this spring has brought the equine industry another step closer to
solving the mystery.
“The main focus of this year’s research has been to zero in on
the caterpillar and try to figure out what is the chemical or biological nature
of the agent that causes MRLS,” said Nancy Cox, associate dean for research
in the University of Kentucky College of Agriculture.
Results from UK’s first-reported 2003 research trial, led by Bruce Webb
and Karen McDowell, indicate the causative agent may be associated with the
caterpillar’s exoskeleton, or outside cuticle. This trial looked at what
happens when different parts of the caterpillar are fed to pregnant mares, and
the only treatments that caused abortions were the ones involving the outside
Fetal losses occurred in five of five mares fed eastern tent caterpillars,
and three of five mares fed exoskeleton (cuticle and related parts). No losses
occurred among mares fed internal parts of caterpillars.
“This is certainly evidence that we’re moving in a forward direction
to narrow our search for the exact cause,” Cox said.
Another recent experiment, led by Manu Sebastian and Bill Bernard, demonstrated
that irradiated Eastern Tent Caterpillars can induce fetal loss in late-term
pregnant mares. This suggests MRLS is caused by a non-infectious agent in caterpillars
(irradiation at sufficient levels has been shown to kill infectious agents such
as viruses and bacteria). The study, conducted jointly by UK and Rood &
Riddle Equine Hospital, was the first experiment in late-term pregnancies which
reproduced a pathological finding similar to naturally-occurring MRLS.
“There’s been tremendous cooperation by our equine industry in
achieving these results,” Cox said. “We appreciate the support we’ve
received from the Kentucky Association of Equine Practitioners, the Kentucky
Thoroughbred Association, and the Kentucky Thoroughbred Farm Managers Club in
helping design and conduct these experiments, as well as provide funds.”
UK researchers also made significant progress this year in terms of pasture
management recommendations and suggestions for caterpillar control.
“After an intensive program of monitoring farms in 2002 and 2003, we
were able to reduce the importance of certain factors, such as cyanide and mycotoxins,
and at the same time gain a better understanding of other risk factors such
as tall fescue endophyte, which is still under study,” said Jimmy Henning,
assistant Extension director for agricultural and natural resources in the UK
College of Agriculture. “We learned a lot about what was going on in horse
pastures the last two springs, and were able to pass that information along
to farm managers.”
Studies conducted by Dan Potter of UK’s entomology department in late
winter and spring determined that certain reduced-risk pesticides effectively
eliminated all sizes of ETC larvae in wild cherry trees. Cherry trees are a
preferred host tree for the insect. Micro-injection of certain insecticides
into the base of trees also gave good control when applied at the right time.
This work was supported by the Grayson-Jockey Club Research Foundation.
Another study showed that a pyrethroid insecticide containing permethrin provided
an effective “barrier” treatment along fence lines to control large
crawling tent caterpillars once they had left the trees and were wandering prior
to cocoon formation.
“Armed with the results of UK experiments linking MRLS with exposure
to Eastern Tent Caterpillars and new information on caterpillar behavior and
control, farm managers developed aggressive management plans that minimized
exposure of pregnant mares in 2003,” said Lee Townsend, UK Extension entomologist.
“On top of that, mother nature provided invaluable help with a caterpillar-specific
disease that dramatically reduced ETC numbers. It certainly proved to be a winning
Foal loss numbers from all causes are down dramatically in 2003. Recent reports
from the University of Kentucky’s Livestock Disease Diagnostic Center
show equine fetal submissions (accessions) for January through May, 2003 are
only half the number for the same period in 2002. In May alone accessions dropped
by 86 percent.
“Other than a very few isolated foal losses that we consider at, or below,
normal levels we’ve basically seen nothing that even approaches the problems
of 2001 and 2002, and that’s very good news,” said Lenn Harrison,
Meanwhile, researchers remain vigilant. Cox said science is a steady process
that gradually eliminates various possibilities and continually narrows the
focus. The work doesn’t stop until the main question is answered.
“Given the discovery that the Eastern Tent Caterpillar is the causative
agent for MRLS, we would be irresponsible not to figure out everything we can
about the mechanisms of the disease,” she said. “Knowing how the
caterpillar affects pregnancy will help our ability to manage pregnancy in mares
in many other scenarios.”
Source: Nancy Cox, 859-257-3333
Writer: Haven Miller, 859-257-4736, ext. 272