Mare Reproductive Loss Syndrome Monitoring Update

Result of Recently Completed Field Study

Ninety-one pregnant Thoroughbred mares on 8 farms in central Kentucky were studied by regular ultrasound examination to monitor the possible effects of exposure to MRLS during 2001. The study was a collaborative project between veterinarians of Hagyard-Davidson-McGee Associates and the University of Kentucky. It involved a comparison between 58 mares exposed to MRLS and 33 not exposed, bred during February and through March 15, 2001.

The results from the study population indicated that MRLS had no effect on the incidence of fetal loss, fetal abnormality and placental and foal weight at birth.

Report from Jimmy Henning, Extension Forage Specialist
Department of Agronomy
University of Kentucky College of Agriculture

Twelve horse farms and one hay farm are being monitored for several soil, pasture and environmental parameters thought to be related to the MRLS outbreak of 2001. Forage samples are analyzed for fungal mycotoxins, alkaloids associated with tall fescue, cyanide and minerals. Soil samples are checked for populations of yeasts and molds.

As of April 25, all sentinel farms have had 4 cycles of sampling completed. Monitoring teams have begun sampling at twice normal speed due to the cooler temperatures and the time of year (coinciding with the onset of MRLS in 2001). To date, no MRLS symptoms have been noted on sentinel farms.

Weather conditions during the week of April 22 have had some similarities to 2001. Horse farms have been alerted to keep early and late pregnant mares up until noon following frost or near-frost conditions as a precaution. In addition, farms are reminded that mowing these pastures after the frost conditions should be a consideration.

Sample results are summarized below:

Fungal mycotoxins: 174 samples have been submitted with 174 results returned. All data are below detectable limits or very low. Small amounts of zearalenone (<500 ppb) have been found by ELISA techniques in 3 samples. Levels of zearalenone below 500 ppb in the absence of measurable levels of other toxins has not been documented to have any ill effects.

Alkaloids associated with tall fescue: 279 samples submitted, 206 results returned. Loline and ergot-type alkaloid values are rising. In all but a few cases, alkaloid levels are low and are not a concern. In a few fields, levels of ergovaline in tall fescue are high enough (>600 ppb) to warrant concern if this tall fescue formed the primary diet for mares in the last 60 days of gestation.

Cyanide associated with white clover: 115 submitted, 76 returned. Levels vary by field and are within ranges reported for white clover. Present values are higher than early spring.

Forage mineral content (including nitrate): 113 submitted, 67 returned. All samples are within normal ranges.

Soil microbial counts: 180 samples submitted, 174 returned. Counts for yeasts and molds are variable but within a normally expected range. Total populations are similar to values reported earlier. Fungi from the Aspergillus, Fusarium and Penicillium genera have been found in quantity on a few samples. Strains from these genera have been known to produce toxins. However, all mycotoxin values in forage are below detectable limits or very low.

Report from Livestock Disease Diagnostic Center
University of Kentucky College of Agriculture

From December 30, 2001 to April 20, 2002, 493 equine abortions had been submitted to the Livestock Disease Diagnostic Center (LDDC) for examination. During this same time period in 2001, 466 equine abortions had been submitted for examination.  During this same time period from 1996-2000 an annual mean of 476.6 equine abortions had been submitted for examination.


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