Recent news from Florida has reported a few isolated cases of Mare Reproductive Loss Syndrome (MRLS) and a recent article from University of Kentucky in TheHorse.Com http://www.thehorse.com/ViewArticle.aspx?ID=11833 has reported increased populations of Eastern Tent Caterpillars. These insect pests have been found to be the direct cause of MRLS and catastrophic loss of mare pregnancies.

It should be pointed out that there has been no widespread epidemic of MRLS this year, as was last seen in Kentucky in 2001, but only that the populations of the insect culprit appear to be rising in some parts of the country, including Kentucky. Research following the 2001 MRLS outbreak which claimed 30% of the entire Kentucky foal crop, strongly supported the hypothesis that accidental ingestion of large amounts of the spiny hairs of the Eastern Tent Caterpillar by grazing broodmares caused conditions that resulted in lethal infections of the placenta and foal in the pregnant broodmare.

While Illinois broodmare owners should not be unduly alarmed, since there are no reports of any local MRLS losses this year, it would be prudent to keep mares away from the "tents" of caterpillars that may be located near grazing areas, and to isolate mares away from any observed migration of caterpillars into grazing areas. The Eastern Tent Caterpillar Moth may lay eggs on several types of trees, but seems to prefer wild cherry, which is commonly found as volunteer vegetation along the edges of pasture where birds have deposited the seeds after consuming the wild cherries. The recent article from University of Kentucky also suggests that the rising population of the Eastern Tent Caterpillars and moths could continue to increase to the point of being dangerous in coming years, so horse owners should be aware of that possibility.

Source: Kevin H. Kline, PhD, University of Illinois, Department of Animal Sciences