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11th April 2011

Histopathology of Mares Aborting Due to Equine Amnionitis and Foetal Loss
by KH Todhunter and AJ Cawdwell-Smith
RIRDC publication number 10/206

In September 2008, Equine Research News profiled the study Equine Amnionitis and Foetal Loss – the role of caterpillars, by AJ Cawdell-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.

The processionary caterpillar (Ochrogaster lunifer) has been demonstrated to cause Equine Amnionitis and Foetal Loss (EAFL). This syndrome occurred in 2004 with increased abortions on various breeding establishments in the Hunter Valley of Australia, causing over 30% of the abortions investigated in that season. This report concerns the changes exhibited at a microscopic level in the pregnant mare after ingesting processionary caterpillars.

The histological aspects of foetuses aborted due to EAFL have been extensively investigated through post-mortems both in the field and experimentally. However, it has been unknown how ingestion of the caterpillar actually causes the abortion or the effect, if any, on the mare’s gastrointestinal tract.

This project was undertaken to investigate the histopathological changes in pregnant mares of being fed macerated whole processionary caterpillars. Caterpillar setae were found to cause a wide range of reactions in the gastrointestinal tract, the mesenteric lymph nodes and the uterus of these mares. By increasing the understanding of the pathogenesis of EAFL, members of the horse industry and veterinarians will be able to better manage brood mare exposure to caterpillars and treatment if exposure occurs.

The full report can by found on the RIRDC website: www.rirdc.gov.au  RIRDC publication number 10/206