Monthly Archives: October 2013

Mare Abortions And Caterpillars - Processionary Caterpillars

Processionary Caterpillars
Photo: Arturo Reina Sánchez

Mare owners have long agonised over why their healthy mares have unexpectedly, and seemlingly without cause, aborted their foals at either 15-45 days or at 9-10 months.

Researchers in Lexington, Kentucky, have attributed these abortions to caterpillars, specifically Malacosoma americanum (eastern tent caterpillar) in America and Ochrogaster lunifer (processionary caterpillar) and Leptocneria reducta (white cedar moth caterpillar) in Australia. They have compiled a data base containing information about the problem, now known as Mare Reproductive Loss Syndrome (MRLS) in the USA and Equine Amnionitis and Foetal Loss (EAFL) in Australia. Equivet Australia reports:

“During 2005/2006 studies at the University of Queensland (Australia) showed that exposure to preparations made from the processionary caterpillars (or their shed exoskeletons) were responsible for causing pregnancy loss in the mare or deficits in the newborn foal. Shed exoskeletons accumulate in the nests as the caterpillars pupate. When the caterpillars leave the nest to migrate, the nest frequently disintegrates and falls onto the ground … The exoskeleton is light and fragile and as it falls can easily drift onto surrounding pasture where it can be picked up by grazing horses.

The results of this Queensland study indicate that the barbed fragments from the setae (small hairs) of the exoskeleton may penetrate the intestinal wall and allow bacteria into the bloodstream thereby causing infection of the placenta and subsequent abortion.”

Eastern Tent - Caterpillars after hatching

Eastern Tent Caterpillars after hatching

Read the rest of the article from Equivet Australia. It discusses the caterpillars’ behavior, what it is that is so harmful to the mare as to potentially cause her to abort, and offers some simple recommendations to reduce the threat to your mares.

Although this is an Australian article, the problem is not exclusive to Australia. As mentioned above, there are caterpillars in America that pose a similar threat, and they can also be found in the UK and throughout northern, central and southern Europe. Read more about the European caterpillars and the threat to trees in this article by Sarah Shailes, The Oak Processionary Moth: A New Pest To UK Oak Trees

Both articles also point out how dangerous the caterpillars can also be to humans “because of a toxin called thaumetopoein contained in tiny hairs on their bodies. Contact or inhalation of the hairs can lead to skin irritation and allergic reactions.” (Sarah Shailes). The Australian report also notes that “some horses grazing under trees populated with caterpillars displayed skin reactions.”

Mares will always abort for one reason or another. However, repeated and multiple abortions are not only heartbreaking, but can be an economic disaster, especially on very large thoroughbred studs.

If you live in an area where there are processionary, eastern tent or white cedar moth caterpillars, you need to read these articles and educate yourself so you can reduce or at least minimize the risk to your mares and their unborn foals.