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May 23, 2002

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

Twelve horse farms and one hay farm have been monitored for several pasture and soil variables to study their relation, if any to MRLS. In addition, blood and urine samples have been collected from selected farms.

To date, 7 cycles of sampling have been completed across all farms. In addition, UK personnel have interviewed and sampled farms that have experienced MRLS symptoms based on a referral basis. Further, with the aid of the Kentucky Association of Equine Practitioners, additional information is being collected as a followup on suspected cases of MRLS.

Some monitoring farms have experienced MRLS symptoms, but no individual pasture or soil microbiological characteristics have correlated consistently to MRLS symptoms.

Follow up visits have consistently found most MRLS symptoms to be related to exposure to eastern tent caterpillars. There are some farms where cases of MRLS do not seem proportional to exposure to caterpillars or distance to ETC host trees. However, some of these visits have been made after ETC migration was mostly complete, so absolute exposure to ETC could not be documented.

Mycotoxins: Low values of dioxynivalenol (DON), T-2 and zearalenone have been found in some pasture samples. However, there are no clear correlations to occurrences of MRLS.

Alkaloids associated with tall fescue: Levels of ergovaline greater than 0.6 ppb have been detected in tall fescue from some fields. As with mycotoxins, these pastures sometimes but are not consistently related to MRLS. There are fields with similar ergovaline values but with no MRLS or fescue symptoms.

Cyanide and forage minerals: Levels of cyanide in white clover are highly variable and are not correlated to MRLS. Levels of calcium and potassium and other measured minerals do not differ greatly among farms and as such are also not correlated to MRLS symptoms. Potassium values are higher in late April and early May sampling periods compared to early March. Nitrate values are within normal ranges for forage crops.

Soil yeast and mold counts: Counts of yeasts and molds continue to be similar to earlier sampling periods. Fungal genera have been found that can produce myctoxins, but mycotoxins have been found only in limited fields and then in low quantities.

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