Could Endophyte-Infected Fescue Cause Lameness in Horses?

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+ horses as hypothesized, they did notice some soundness issues--specifically hoof sensitivity--in horses of that group.

"The most unexpected observation was just how lame some of the horses on the E+ diet became," Douthit explained. "I expected that we might see some circulatory changes, but I definitely did not expect full-blown lameness in those horses."

Because decreased digital circulation was not observed and the study population was relatively small, the researchers were reluctant to conclude that diet was directly responsible for the lameness appearing in E+ horses. However, they did report that the "lameness was obvious enough and of large enough magnitude that it might be prudent for owners to limit the exposure of their horses to endophyte-infected fescue."

The study, "The impact of endophyte-infected fescue consumption on digital circulation and lameness in the distal thoracic limb of the horse," was published in September in the Journal of Animal Science. The abstract is available online.

Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.