Remove mares from affected pastures to help prevent mare reproductive loss syndrome (MRLS).
The exact pathogenesis of MRLS is unknown, but exposure to/ingestion of “hirsute” or hairy eastern tent caterpillars appears to be a risk factor. Early and late-term abortions have been reproduced by oral administration of whole eastern tent caterpillars (Malacosoma americanum) or their exoskeletons.
Eastern tent caterpillars were associated with a large outbreak in Kentucky in 2001-2 where over 3000 pregnant mares aborted. Other episodes have been seen in Florida (2005) and Australia (2007) with exposure to other animals of hirsute caterpillars.
The most current theory – damage to the oral mucosa or intestinal lining by the setae (spines) of the caterpillars introduces bacteria that causes bacteremia and subsequent infection of the fetus and/or placenta.
Early embryonic loss, abortion, stillbirths, weak foals, and infected foals are seen. Swollen umbilical cords are also often seen in aborted fetuses.
Feeding hay and removal of wild cherry trees, a major food source for the caterpillars, is also beneficial in reducing the incidence of MRLS abortion.
