This is the fifth in a series of ongoing experiments designed to identify the factor or agent responsible for fetal losses due to Mare Reproductive Loss Syndrome (see MRLS reports of June 12, 2002, October 25, 2002 and June 6, 2003, at this WEB site: www.uky.edu/Agriculture/VetScience/mrls/index.htm). These experiments are funded by the University of Kentucky College of Agriculture and USDA:ARS.

Eastern Tent Caterpillars (ETC) were collected in central Kentucky in the spring of 2003 and stored at -80ºC until used. Gilts in mid-gestation were paired so that one gilt from each pair was fed a normal ration (n=5 gilts) and the second gilt of each pair received ETC (40 g/gilt/day for 10 days) mixed into the normal ration.

Two of five gilts fed ETC aborted their entire litters while none of the five control gilts aborted. The two ETC-fed gilts which aborted, along with their non-treated pairs, were euthanatized and necropsied 1-3 days after the abortions occurred. The remaining gilts were euthanatized and necropsied 29 days after the onset of the trial.

Streptococci bacteria were isolated from fetuses of all gilts fed ETC, whether or not they aborted, and from fetuses of one control gilt. Bacteria isolated from the control fetuses were less numerous and of a different strain than those isolated from fetuses of ETC-treated gilts.

Of particular interest was the identification of what appear to be caterpillar setae (hairs) in the alimentary tract of gilts fed ETC but not of control gilts. At this time we cannot be certain if the hairs contributed to the abortions in the two treated gilts or to the presence of bacteria in fetuses of the treated gilts.

This experiment demonstrated for the first time that ETC can cause abortion in a non-equid in a manner consistent with MRLS, and indicates that domestic pigs may be a useful model for studying the syndrome.

Source: University of Kentucky - College of Agriculture - 5th September - 2003