Caterpillars cause abortion in Australian mares

Caterpillars cause abortion in Australian mares Researchers from The University of Queensland have found hairy caterpillars are responsible for causing abortions in Australian mares. Dr Judy Cawdell-Smith and Professor Wayne Bryden, from UQ's School of Animal Studies, found mares exposed to processionary caterpillars were likely to miscarry. "This is an unusual form of abortion that was first reported in Australia in 2004 and is similar to a condition reported in Kentucky in 2002," Dr Cawdell-Smith said.

Eastern Tent Caterpillars  - the cause of the US equine condition, Mare Reproductive Loss Syndrome.

"Researchers in Kentucky identified Eastern Tent Caterpillars as the cause of the US equine condition, Mare Reproductive Loss Syndrome."

Similar equine abortion cases were reported in the Hunter Valley, the heart of Australia's Thoroughbred breeding industry, in 2004.

"Studies conducted by veterinary epidemiologist, Professor Nigel Perkins, suggested the abortions were caused by caterpillars or poisonous plants," Professor Bryden said.

"No poisonous plants were found on any of the stud farms where mares aborted."

"Caterpillars were identified as the cause of the US problem but the same caterpillars don't exist in Australia. However, other related caterpillars were found on the affected Australian stud farms."

Processionary caterpillars ( Ochrogaster lunifer) have a brown head, and a grey body with dark bands covered with numerous long, white irritant hairs. These hairs (and those of the adult moths) can cause a skin rash if touched. Fully grown caterpillars are 4- 5cm long.

The caterpillars spend the day inside a silken bag or nest - hence the name given to the adult moth "Bag Shelter Moth". At night they emerge to feed, their preferred host plants being wattles (Acacias)  and Beefwood (Grevillea striata ).

When travelling they form a procession, each caterpillar following a silken trail left by the one in front. Lines containing up to 135 caterpillars have been reported.

"If you've ever seen a hairy caterpillar, it is unlikely that a horse would eat a whole one," Professor Bryden said. "What's more likely is that the caterpillar's exoskeleton - which is much harder to see in the grass - is picked up by the horse while it is grazing.

"In our studies, both whole caterpillars and exoskeleton caused mares to abort."

The researchers believe ingestion of the caterpillar changes the permeability of the intestinal wall, allowing bacteria to pass into the horse's circulation and through the placenta.

"The subsequent infection caused by the bacteria in the fetus results in abortion," Dr Cawdell-Smith said.

"These bacteria are found in the intestine of mares and normally don't cause a problem.

"Interestingly, mares that abort have no ill effects or evidence of illness."

This research was funded by the Rural Industries Research and Development Corporation and the Hunter Valley Equine Research Centre.

Reproduced with kind permission of Mark Andrews BVM&S CertEP MRCVS
© Copyright Mark Andrews  - Equine Science Update 2008

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