Mare Reproduction Loss

Mare Reproductive Loss Syndrome in Alachua County

Three confirmed cases of Mare Reproductive Loss Syndrome (MRLS) have been reported in Alachua County. The diagnosis was made by Dr. John Roberts, pathologist at the University Of Florida College Of Veterinary Medicine. Dr. Roberts worked in Kentucky during the outbreak of MRLS in 2001-2002.

MRLS is caused by the consumption of the Eastern Tent Caterpillars (Malacosoma amercanum). After 2-10 days of consuming the caterpillars, mare may abort or foals may be born weak. The Eastern Tent caterpillars can be found in many deciduous trees but seem to prefer wild cherry, apple and crabapple. Adult moths lay eggs in webs in the trees and the eggs hatch in temperate weather of spring. The larvae feed in the trees as they develop then drop off. The caterpillars crawl around, consuming grass, and other vegetation as they grow. This is the phase of development that they pose a danger to horses which may inadvertently consume them. An individual caterpillar only crawls and feeds for about two days before climbing a tree or post and pupating. There may be several weeks when caterpillars can be found active. March seems to be the month for Alachua County.

Dana Zimmel, IFAS Extension Equine Veterinarian strongly recommends that all abortions and foal deaths occurring during caterpillar activity receive a post- mortum evaluation.

Mare owners should inspect their pastures for cherry trees and caterpillars. If possible, remove horses from pastures where you find active caterpillars until they are gone

Source: Dr. Saundra TenBroeck, Extension Horse Specialist, UF

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