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8th June 2012




In September 2008, Equine Research News profiled the study Equine Amnionitis and Foetal Loss- the role of caterpillars, by AJ Cawdwell-Smith and WL Bryden. The research was a result of a spate of abortions in the Hunter Valley in 2004 which exhibited unusual and consistent symptoms. A link was found between hairy caterpillars (Ochrogaster Lunifer) and the syndrome Equine Amnionitis and Foetal Loss (EAFL).


Further research has now been completed on the mechanisms by which caterpillars may cause abortion in pregnant mares, in the study Histopathology of Mares Aborting due to Equine Amnionitis and foetal Loss. Until now, it has been unknown how investigation of caterpillars actually causes the abortion or the effort on the mare’s gastrointestinal tract.


With a greater understanding of how mares are affected, breeders may be able to manage the conditions caused by EAFL before exposure or abortion occurs. The report is targeted at vets and vet pathologists, and ultimately involves any person who is involved in breeding horses. The aim of the study was to determine the change to tissue and organs that may occur in pregnant mares after ingesting caterpillars. The researchers used three horses that had been fed macerated whole processionary caterpillars, and on untreated control. The horses were euthanised and submitted to post-mortem examination of the gastrointestinal tract, reproductive tract, organs and lymphatic tissue. Samples were examined for the presence of caterpillar hairs within any tissue and subsequently reactions.


Researcher Results

Hairs (or setae) were found throughout the tissue of the mares including the gastrointestinal tract, liver, lymph nodes and uterus causing a range of reactions. The research showed there were a number of mechanisms by which ingested caterpillar setae could enable bacteria to move from the gastrointestinal tract to the foetal membrane, thus playing a part in foetal loss.


The findings of the research reinforce the importance of limiting exposure of horses to processionary caterpillars, with an emphasis on pregnant mares due to the possibility of setal fragments causing a number of conditions including gastrointestinal disease, peritonitis, abortion and possibly chronic placentitis. Managing caterpillar presence in areas where horses are grazed is important and may be done by working with entomologists, land care agents, agronomists and other agricultural professionals.

RIRDC publication number 10/206

Available for download from the RIRDC website: www.rirdc.gov.au