UK Releases New Eastern Tent Caterpillar Study; Frozen Insects Cause Abortion

The University of Kentucky College of Agriculture released on Friday the results from a collaborative project involving the departments of Veterinary Science (Dr. Karen McDowell, Gluck Equine Research Center and Drs. Neil Williams and Mike Donahue, Livestock Disease Diagnostic Center) and Entomology (Dr. Bruce Webb and Mr. Walter Barney). This is a follow-up trial to two projects conducted in April, May and June, 2002.

This experiment was designed to test the hypothesis that the factor associated with Eastern tent caterpillars (ETC) that causes abortions in pregnant mares is labile to autoclaving. Fourteen pregnant mares were divided into 3 treatment groups. For 10 days the mares were fed ETC that were collected in Spring 2002 and stored frozen, ETC stored frozen that were subsequently autoclaved, or gypsy moth caterpillars (GMC) that had been stored frozen. The caterpillars were mixed with sweetened oats or sweet-feed (not containing mycotoxin binders), and mares were fed individually from feed buckets. After eating, the mares were housed communally on grass paddocks supplemented with hay.

Pregnancy loss rates were 3 of 5 for mares fed frozen ETC, 0 of 5 for mares fed frozen-autoclaved ETC, and 1 of 4 for mares fed GMC. The ultrasound examinations (increasing echogenicity of the fetal fluids, followed by fetal death) and laboratory reports (isolation of Streptococcus and/or Actinobacillus bacteria from the fetuses and fetal membranes) of two of the ETC-fed mares that aborted were consistent with signs of MRLS. Fetal fluids for the third ETC-fed mare that aborted showed increased echogenicity on ultrasound examinations, but the bacteriologic results were not consistent with MRLS (the aborted fetus was recovered from the turn-out paddock). For the mare fed GMC and which aborted, the signs of pregnancy failure were not consistent with MRLS. That fetus, approximately 40 days at the beginning of the trial, failed to grow at a normal rate and subsequently died. The allantoic fluid volume appeared to decrease prior to fetal death, without a marked increase in echogenicity. We cannot be certain if GMC caused fetal loss in the one mare, or if she would have lost the pregnancy regardless of treatment.

UK concluded from the study that the factor associated with ETC which causes abortions in pregnant mares is labile to autoclaving.