The spring rains have helped pastures with fescue grass turn green. But during foaling season, these lush fescue pastures can create problems for pregnant mares.

Here, David Anderson, DVM, MS, Dipl. ACVS, head of Large Animal Clinical Sciences at University of Tennessee (UT) College of Veterinary Medicine, and Carla Sommardahl, DVM, PhD, Dipl. ACVIM, clinical associate professor and section head of Large Animal Medicine at UT talk about fescue grass toxicity and management options.

Tall fescue is a grass which grows on over 35 million acres of land in the United States. As many as 700,000 horses graze fescue pastures or are fed fescue hay each year. Many of these pastures contain fescue that is infected with an endophytic fungus that is toxic to horses. When the horse ingests the grass or hay made from these pastures, it is steadily ingesting alkaloids produced by the fungus.

Owners might not realize is that there are some significant health risks associated with broodmares and young horses eating endophyte fungus-infected (EI) tall fescue pasture or hay. Both the mare and the foal can be affected by these toxic alkaloids produced by the fungus. Some health problems associated with fescue toxicity include:

  • Prolonged gestation in mares;
  • Dystocia (foaling difficulty);
  • Decreased to no colostrums or milk production; and
  • Decreased growth rates in weanlings and yearlings in some studies, if forage is not supplemented with grain.

Some of these problems can be minimized with careful management of horses and pastures. Follow these management tips from the American Association of Equine Pract