May 31, 2001

Kentucky Foal Death Problem Unlikely Here

The cause of an unusual epidemic of deaths of fetuses and young foals on Kentucky horse farms has apparently been traced to tent caterpillars ingesting a toxin from wild cherry trees.

The foal deaths, referred to as Mare Reproductive Loss Syndrome, coincided with an outbreak of Eastern tent caterpillar in Kentucky. Tree hosts for these caterpillars include cherry trees, which are often present in pastures where horses are grazing. Leaves of cherry trees contain cyanide, and caterpillar larva tested in Kentucky have been strongly positive for cyanide. Ingestion of the larva by grazing mares has apparently led to cyanide poisoning and fetal or foal death.

According to Phil Glogoza, extension entomologist at North Dakota State University, the outbreak of tent caterpillars in eastern North Dakota and northwestern Minnesota this spring has been the forest tent caterpillar, a related but different species.

Is there a danger of a similar poisoning problem in this area? While horse owners in the area might be concerned, Glogoza says there is no natural toxin in the caterpillars. Without the presence of cyanide-containing plants, the poisoning situation would not exist, so the forest tent caterpillar is not likely to present a risk.

Extension veterinarian Charlie Stoltenow says the Kentucky situation, if it is being caused by the caterpillars ingesting cyanide from cherry leaves, is a very rare event that is no doubt very localized. He has had some calls from concerned horse owners in the area affected by the forest tent caterpillar outbreak but says the danger of any similar event in this area is very small.

Glogoza says the preferred tree hosts for the forest tent caterpillar include aspen, maple, oaks, linden, birch, cottonwood, basswood, ash and others. None of these are known to contain cyanide that could be passed on to horses or other livestock.

Caterpillar feeding for this season should continue until about mid-June, he says.

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Source: Phil Glogoza,(701) 231-7851, pglogoza@ndsuext.nodak.edu
and Charlie Stoltenow,(701) 231-7522, cstolten@ndsuext.nodak.edu
Editor: Gary Moran, (701) 231-7865, gmoran@ndsuext.nodak.edu