UK College of Agriculture: Mare Reproductive Loss Syndrome Briefing 5/17/01

From the UK College of Agriculture
The following information is provided with respect to progress of the investigation into the Mare Reproductive Loss Syndrome.

The coordinating group has been studying details of mare breeding records for 2001. This identified more precisely the time of the critical insult giving rise to the syndrome, between April 17 and 23. Based on information provided, late abortions, the birth of weak foals, and early fetal losses appear to be linked to the same causal event. The investigating group is extremely appreciative of farms that have provided early fetal loss information and will be requesting further data to assist in our research investigation. Information on early fetal losses and daily figures on submissions to the Livestock Disease Diagnostic Center (LDDC) indicate the incidence has fallen over the last seven days.

Studies undertaken at the LDDC on equine samples over the previous three weeks have found no evidence whatsoever of an infectious or contagious disease.

Examination of fetal and foal samples strongly support that the presence of bacteria is secondary to a primary insult. Pathological findings from early fetal losses are inconclusive. Gross and histopathological lesions from late fetal losses are consistent with ergot toxicity but are not characteristic.

Detailed inspection of pastures grazed by affected mares has been undertaken by agronomists from the College of Agriculture, University of Kentucky. The investigations have so far revealed no clearly identifiable source of the syndrome.

The list of possible candidates including mycotoxins, fungal endophytes, phyto-estrogens and other compounds in pasture are under intensive investigation. Fusarium mycotoxins remain a candidate with many pasture samples proving positive for zearalenone, an estrogenic mycotoxin that has been shown to cause reproductive, cardiac, and eye problems in horses and other species. With the notable exception of Moldy Corn Poisoning (equine leukoencephalomalacia), little is known with respect to the toxicological effects of mycotoxins in horses.

A considerable difficulty encountered during the early stages of the investigation was that reliable and rapid assays to identify a variety of suspect agents were not available. The coordinating group has established panels of rapid and sensitive assays for zearalenone and three other mycotoxins as well as for ergot alkaloids in pasture and urine, which will provide a much faster turnaround for sample analysis.

Daily pasture samples are being taken on selected farms to identify and monitor the levels of several highly suspect environmental toxins. Pasture samples taken and stored prior to May 5 are considered critical to the investigation. Samples of hay baled before May 5 are highly desirable for analysis and should be submitted to Dr. Tom Tobin's laboratory at the Department of Veterinary Science, Gluck Equine Research Center. Hay samples are best "core sampled" with which your county agent can assist. In the absence of a corer, take a flake from the middle of the bale and submit for analysis. Alternatively, call Dr. Steve Jackson at 859/873-9218.

Over 100 pasture samples have been taken, of which 70% are being processed, and all of which will be subject to further analysis. In addition, urine samples from affected mares as well as blood samples have been taken and are being analyzed.

Examination of tent caterpillars has revealed high levels of zearalenone. The significance of this finding is not clear. Caterpillars and their excrement have tested negative for cyanide.

This syndrome is unparalleled in its intensity and severity. The horse industry of Kentucky together with private equine consultants, state and federal agencies and the scientific community, locally, nationally and internationally, has come together in a tremendous unified effort to solve this problem.

Further information will be provided as it becomes available. Information is posted on the UK web site at