When tall fescue first arrived in the United States during the 1940s, it was considered a wonder grass. It was easy to establish, it yielded a good amount of forage, it was tolerant of a wide range of management regimens, and it could handle a variety of climatic conditions as well as sustain heavy foot traffic. Farmers and ranchers embraced the new grass with great enthusiasm and, in a relatively short span of time, some 35 million acres of land in the United States was planted with tall fescue.


Then, the honeymoon ended. Horse breeders noticed that they were having foaling problems with some mares which were grazing tall fescue grass or being fed tall fescue hay. Cattle producers had problems, too. The cattle grazing on the grass during the late summer months were unthrifty, and there was a drop in milk production from dairy cows.

Agriculture turned to research to find out why these things were happening. In the late 1970s, it was discovered that much of the tall fescue contained a fungal endophyte that can have highly deleterious effects on animals consuming it. The scientific name for this fungal endophyte is Acremonium coenophialum.

Its effect on pregnant mares can be particularly severe. Mares grazing on infected tall fescue pasture or fed infected tall fescue hay might have prolonged gestation or a tendency to abort, can develop an abnormally thick and/or tough placenta, can retain the placenta after giving birth, often have difficulty in the birthing process (dystocia), and might have no milk (agalactia) for the foal once it is born–if, indeed, the foal is born alive and remains alive after birth.

There were some positives early on in the battle against fescue toxicosis. First, it was discovered that if mares were removed from infected tall fescue several months before foaling, the endophyte’s harmful effects dissipated for the most part.

Next, scientists developed a fescue gras