May 17, 2002
Report from Jimmy Henning, Extension
Department of Agronomy
University of Kentucky College of Agriculture
Pasture Update and Recommendations
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
It should be clearly understood that following these recommendations cannot
guarantee that subsequent cases of MRLS will not occur, but should greatly
reduce the risk.
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.
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