Horse breeders in parts of the country frequented by endophyte-infected tall fescue are likely aware of the problems the forage–more specifically the fungus inside the forage–can cause in broodmares. But this toxin’s effects on the other half of the breeding puzzle–stallions–remain widely unknown.

Richard Fayrer-Hosken, BVSc, PhD, Dipl. ACT, ECAR, MRCVS, professor of theriogenology at the University of Georgia College of Veterinary Medicine and author of a preliminary study on the topic, spoke Oct. 11 at the Gluck Equine Research Center Veterinary Science Seminar, in Lexington, Ky., where he explained that the effects of ergot alkaloids in colts and stallions do not appear as negative as those in broodmares.

Tall fescue covers an estimated 35 million acres in the United States, including pastures, high-traffic foot paths, golf courses, and backyards. A majority is endophyte-infected (EI). An endophyte is a fungus that lives symbiotically within the host plant and is not visible to the eye. The endophyte produces toxic alkaloids that, when eaten, cause different disorders including tall fescue toxicosis.

In broodmares, Fayrer-Hosken explained, EI tall fescue can cause numerous problems including increased early embryonic mortality, agalactia (poor milk let-down), placental edema (fluid swelling), retained placenta, increased abortion rate, increased gestational length, and increased rate of newborn mortality