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May 1, 2002



The University of Kentucky College of Agriculture is releasing today preliminary results from a collaborative project involving the departments of entomology, veterinary science and the livestock disease diagnostic center.  Early results from this ongoing research project show elevated levels of foal loss in mares exposed to both the eastern tent caterpillar (ETC) and the caterpillar's waste, which is called frass.

UK researchers emphasize that these experimental preliminary results apply only to this project.  This experimental trial is in no way expected to be a predictor of the extent of MRLS that may be observed on farms this year.

An intensive survey of horse farms last year by scientists at UK's Gluck Equine Research Center found a strong association between the presence of eastern tent caterpillar and the incidence of MRLS.  This ETC-MRLS research project was designed to determine if this association was simply a correlation, or if tent caterpillars were causally associated with MRLS.  This trial is ongoing.

The experiment involved 29 pregnant mares which were separated into three experimental treatment groups.  In the first group mares were exposed for 6 hours each day to increasingly high levels of ETC and their frass.  In the second group mares were exposed only to the insect's frass.  In the third group, called the control group, mares were handled identically to the experimental treatments but received as little exposure to ETC larvae or frass as possible. Mares were on pasture only, not hay.

In the first treatment with ETC and frass, 6 of 10 mares have lost their foals.  In the second treatment with only frass, 6 of 9 have lost foals.  In the control group receiving reduced exposure to ETC or frass, 3 of 10 mares have lost their foals.

Results of examination of a fetus from a mare in the frass experimental group are consistent with those associated with early fetal losses suffered in 2001.

Researchers stress that the project is not yet finished, and the results do not show a statistically significant result. Other possible causes for fetal losses in this experiment are also being investigated. It should also be noted that mares in this project were exposed to higher populations of ETC than would occur naturally.

Although these results apply only to this project, UK continues to recommend that exposure of pregnant mares to eastern tent caterpillars and caterpillar frass be limited as advised in the MRLS advisory of April 26, 2002.  The investigation into the cause or causes of MRLS continues.

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