Using Mature Hay for Bedding: Potential for Tall Fescue Toxicity

Ergovaline levels over 200 ppb (parts per billion) in mature hay can cause fescue toxicity in pregnant mares.

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Due to the drought this past summer, straw is expected to be in short supply and more expensive than in recent years. A number of horse farm managers have chosen to harvest overmature pastures for bedding rather than pay a premium for straw.

On the surface, it makes sense to use this stemmy hay for bedding. But, be cautious when using it for bedding pregnant mares during their last trimester. It is not uncommon for horses to eat some of their bedding, especially if it is hay, and ergovaline levels over 200 ppb (parts per billion) can cause fescue toxicity in pregnant mares.

Surveys show Central Kentucky horse pastures often contain more than 25% tall fescue. Because tall fescue’s stem and seed head contain the highest levels of the toxin ergovaline, there is a good chance mature hay could contain toxic levels. In other areas of Kentucky and in surrounding states, tall fescue often makes up more than 50% of horse pastures.

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

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