Endophytes–fungi that benefit some grasses such as fescue by acting as a natural insect deterrent–have proven harmful to grazing animals, such as cattle and horses.

Endophyte-infected tall fescue, for example, has long been associated with reproductive problems and abortion in mares. But new research indicates it could also cause some forms of equine lameness.

A group of researchers from Kansas State University (KSU) recently set out to evaluate the effects of endophyte-infected fescue–a common forage found in horse pastures throughout the United States–on horse digital circulation and forelimb lameness.

"If one has fescue pasture, it is highly probable that it is endophyte-infected; most fescue pastures are (infected)," relayed Teresa Douthit, PhD, assistant equine nutrition professor at KSU and lead researcher of the study.

The team employed 12 unshod horses divided into two groups during the 90-day study. Researchers acclimated one group to a diet high in endophyte-infected fescue seeds and hay (Group E+) until reaching endophyte levels reported to elicit toxicity in cattle (but likely containing levels lower than most fescue pastures in the central United States). Horses in the other group consumed a low-endophyte (E-) diet.

Every 30 day, horses underwent a clinical lameness evaluation, and the team evaluated digital circulation via ultrasound and thermographic imaging.

Study results showed that the endophyte-infected fescue did seem to have an effect on horses, but not in the way researchers thought it might. While the team did not observe a trend towards reduced circulation in E+ hor