Revised:  05/22/2008

Memo for June 14, 2006













New Jersey Department of Agriculture, Division of Animal Health



To: Veterinarians

From: Nancy E. Halpern, D.V.M., State Veterinarian

Date: June 14, 2006

Re: MRLS in New Jersey; Pathology Results Consistent with MRLS



     A horse farm in Northern New Jersey experienced high abortion rates in mares that were in fields with large populations of tent caterpillars. Recent pathology results, received the week of June 5th, 2006 on aborted foals from the farm sent to University of Kentucky’s Gluck Equine Research Center, were consistent with Mare Reproductive Loss Syndrome (MRLS).


     MRLS was first recognized in 2001 as an outbreak of fetal deaths, foals born weak, and late-term abortions in Kentucky. A strong association exists between the presence of unusually large numbers of eastern tent caterpillars and MRLS. Pregnant mares experimentally fed the caterpillars typically abort within days.


     MRLS was again confirmed in Florida during March and April of 2006. Several mares aborted after exposure to eastern tent caterpillar.

Experts say there is no question that the eastern tent caterpillar causes this abortion syndrome. The only question is - what is it about the caterpillar that causes the problem? It may be the plant(s) the caterpillar eats, the caterpillar’s own biochemical interactions, or its setae (hairs). There are 15 varieties of tent caterpillars, and the eastern tent caterpillar (maybe the western tent caterpillar) is the only one that causes the syndrome.


     Control of the syndrome involves preventing exposure of pregnant mares to the caterpillars. Exposure to dead caterpillars and possibly their excreta/feces may be a threat to the pregnant mares.


     Control of the tent caterpillars is best accomplished in early spring, by identifying and removing egg masses from trees, although other controls do exist.


     Please contact Donna Folk of Rutgers Cooperative Extension at (908) 475-6503 for further information concerning tent caterpillar control. Contact your veterinarian if your horses exhibit any unusual signs of infertility, abortion or weak foal births. Although MRLS is not a required reportable disease, the Division of Animal Health requests your cooperation in reporting any unusual incidents of the signs described above to (609) 292-3965.






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