Mature Hay Bedding has Potential for Tall Fescue Toxicity

With budgets tight, a number of horse farm managers have reduced costs by using a hay harvest of overmature grass pastures for bedding.

On the surface it makes sense to bed stalls with this stemmy hay. But be cautious when using it for pregnant mares in their last trimesters. Some horses eat their bedding, especially if it is hay, and ergovaline (an alkaloid produced by a fungus that lives inside the plant) levels above 200 ppb (parts per billion) in the hay can cause fescue toxicity in pregnant mares. UK's surveys show that Central Kentucky horse pastures often contain more than 25% tall fescue, and since the stem and seedhead of tall fescue contain the highest levels of the toxin ergovaline, there is a good chance mature hay contains toxic levels. In other areas of Kentucky and in surrounding states, tall fescue often makes up more than 50% of horse pastures.

If overmature grass hay is used as bedding for pregnant mares, first have it tested for ergovaline concentration at the University of Kentucky Veterinary Diagnostic Laboratory (VDL, formerly the Livestock Disease Diagnostic Center) in Lexington. Work with a veterinarian or county agent to submit samples. Samples should be taken from the bales with a hay probe, just as you would take samples to test for hay quality. Make sure the sample submitted is comprised of cores from five to 10 separate bales from each hay cutting. In most counties the county agent or a farm service store can loan a hay probe for sampling. The cost of the ergovaline test is $50 per sample. For more information, contact Cindy Gaskill, DVM, PhD, a clinical veterinary toxicologist at VDL, at 859/257-7912.

If you reside in Central Kentucky, a representative from the University of Kentucky Pasture Evaluation Program can come to your farm, sample your hay, submit it to the VDL, and send you the results with an interpretation. For more information on the Pasture Evaluation Program, visit and click on "Testing Hay for Ergovaline."

Ray Smith, PhD, an associate professor and forage extension specialist at the University of Kentucky, provided this information.

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