This insect is now leading suspect in cause of Mare Reproductive Loss Syndrome.

This insect is now leading suspect in cause of Mare Reproductive Loss Syndrome.

Researchers Shift Attention to Eastern Tent Caterpillar

Discussions of results obtained to date by several scientists and consultants working on the investigation into the cause of Mare Reproductive Loss Syndrome (MRLS) have caused the investigation to shift to a more thorough examination of the potential role of the Eastern Tent Caterpillar (ETC) in MRLS.

Although several potential causal agents have not been totally eliminated, mycotoxin test results obtained to date, have been mostly negative. Results from sampling of hay baled prior to May 5th analyzed to date have also tested negative for mycotoxins.

Investigations into the role of ergot alkaloids in MRLS are also yielding results that do not fit the profile of the causal agent, including symptoms from the field, and pasture/ hay composition and testing.

However, the roles of mycotoxins and ergot alkaloids have not been totally ruled out at this point in the scientific investigation and either may still play a contributing role to the cause of MRLS.

The Eastern Tent Caterpillar is a pest native to North America, populations of which fluctuate from year to year. ETCs prefer wild cherry trees as their primary host, but also nest on apple, crabapple, and other trees. The ETCs overwinter as an egg within an egg mass of 150 to 400 eggs. The caterpillars hatch about the time buds begin to open on trees. It takes approximately 4 to 6 weeks for the caterpillars to reach mature size. In years of massive infestations of ETCs, they can nearly defoliate trees, then are forced to move to find additional food sources prior to being full grown. Once full grown, the caterpillars pupate, emerging as a moth about three weeks later. For more detailed information about ETCs go to the web site:

Visual correlations on several farms that have experienced MRLS show the presence of wild cherry trees in or near fields where affected mares were grazing, but we still do not know if there is a one-to-one correlation between the presence of wild cherry trees and incidences of MRLS. Since ETC's primary host tree is the wild cherry, a very in-depth look is now underway to determine if and how ETCs or wild cherry trees have roles in the cause of MRLS.

Heavy infestations of ETC were reported last year (2000) as well as this year. As of today, ETC moths have been sighted in the area, so their pupate stage began approximately the end of April/ first of May. In review of past UK publications of Kentucky Cooperative Plant Pest News and Kentucky Pest News, the last heavy infestations of ETCs occurred in Central Kentucky during 1979, 1980 and to a lesser extent in 1981. In those reports, host trees (wild cherry) were nearly defoliated and caterpillars were moving by April 27th in 1979 and by May 9th in 1980. Information for 1981 is not as complete, but large numbers ETC egg masses were observed on trees and were beginning to hatch by April 7, 1981. Early fetal loss in mares had occurred in the area with an undefined causal agent in both the 1980 and 1981 foaling seasons. Review yesterday's briefing for the similarities in weather conditions of the three years, 2001, 1980, and 1981.

As previously reported, examinations of caterpillars and their excrement have initially tested negative for cyanide, but revealed high levels of the mycotoxin, zearalenone. (Briefing dated May 17, 2001). Also reported in the same briefing, we believe the critical insult that gave rise to MRLS occurred between April 17 and 23, based upon detailed studies of mare breeding records. As reported in yesterday's briefing, Central Kentucky experienced a very cold March, followed by a very warm April, with frost/ freeze occurring on April 17 and 18. We also believe that ETCs were moving during this time period as they had defoliated trees and were not yet full grown.

We strongly emphasize that the cause for Mare Reproductive Loss Syndrome has not yet been determined and many options are still under consideration and investigation as to its cause.

The Kentucky Thoroughbred Association will also broadcast fax this brief to horse farm owners or managers on a request basis. To be added to that list, please contact Vickie Garcia at 1-800-552-3781 or locally at 381-1414.

The scientific investigating team, with the Kentucky Association of Equine Practitioners and the Kentucky Thoroughbred Farm Managers Club will hold an information sharing session on Thursday, May 24th similar to the session held previously on May 10th. The information sharing session will begin at 5:00 pm at the Keeneland Sales Pavilion. The entire session will be web-cast live from the web-site: