College of Agriculture
Veterinary Science	Mare Reproductive Loss Syndrome Index Page

May 17, 2002

Report from Jimmy Henning, Extension Forage Specialist
Department of Agronomy
University of Kentucky College of Agriculture

Many questions have been raised about whether it is safe to increase time on pasture for mares or mares and foals. Based on extensive pasture sampling, consultation with practicing veterinarians, last year’s history and current field observations, the following are considered the best facts and recommendations regarding pasture use at this time.

• No causal agent for MRLS has been identified, and therefore it is impossible to know the extent of its distribution in any given field.

• Pastures that have defoliated cherry or ornamental trees in, around or near them have been consistently implicated in observed cases of MRLS. Limiting time on a pasture (with cherry trees or caterpillar exposure) has not been enough to totally eliminate MRLS.

• However, longer pasture turnouts should be acceptable on fields with no history of caterpillar travel or migration, and/or that have had good caterpillar control. If a tree has been sprayed but is still defoliated, you should consider that area around that tree to be potentially toxic.

• Areas of a pasture that have been influenced by the eastern tent caterpillar, such as under defoliated trees, should be fenced off and not used for pregnant mares.

• No mycotoxin or other pasture parameter currently being monitored has shown to be consistently related to cases of MRLS (early or late loss) at this time. Pasture characteristics being monitored include fungal mycotoxins, soil microbial (fungal) counts, cyanide content of white clover, mineral content of the forage and alkaloid content of tall fescue.