MRLS Monitoring Update

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 considered 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 June 6, all sentinel farms have had 8 or 9 cycles of sampling completed. There have been EFL cases noted in sporadic and low numbers on monitor farms within the last two weeks.

Sample results are summarized below:

Fungal mycotoxins: Small amounts of zearalenone, T2 and DON have been found by ELISA techniques in some samples. Some compounds have been detected that appear to be mycotoxins using ELISA techniques but that are not confirmed by thin layer chromatography (TLC) followups. These compounds appear to be correlated to the occurrence of MRLS symptoms. Research into the nature of these compounds and their role, if any, in MRLS is ongoing.

Alkaloids associated with tall fescue: 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 in white clover and forage mineral content (including nitrate) are within normal ranges.

Soil microbial counts: Counts for yeasts and molds are variable but within ranges that have been seen across the season. Counts are not correlated with onset of MRLS symptoms. Fungi from genera have been found that are known to produce mycotoxins. However, mycotoxin values in forage are below detectable limits or very low for most samples.

Comments on Pasture Turnout

We are approaching a point in 2002 where, for several reasons, keeping mares up is impractical and possibly endangering the health of mares and foals. The UK Pasture Monitoring Oversight Committee met on June 4 to discuss this issue with the aim of assessing MRLS risk and refining pasture recommendations for horse farm managers.

Based on pasture monitoring observations and information from the farm managers and veterinary practitioners on the Oversight Committee, the risk of MRLS due to more general pasture turnout is low and declining, but currently not zero.

At this time in 2001, general pasture turnout had already occurred based on University of Kentucky College of Agriculture recommendations. However in 2002, caterpillar emergence and travel were spread over a longer period of time compared to 2001. This longer migration period may be contributing to the continuing occurrence of sporadic cases of early fetal loss.

Information so far derived from the research and monitoring program does not provide a guarantee of pasture safety, especially on fields where there have been MRLS cases or where caterpillars were known to be present (independent of host tree or shrub). Some fields that have caused problems in 2002 have the ability to induce MRLS symptoms even after the caterpillars are gone. It is impossible to know if these late MRLS cases received the insult earlier and are now showing symptoms or if some agent is still active on those pastures. There is currently no way to predict the MRLS toxicity of a pasture based on a known assay.

The farm managers on the Oversight Committee did indicate that they were going to more full time turnouts but in general were avoiding those fields with a history of MRLS.

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