Tall fescue soon gained a reputation for livestock health problems, resulting in poor animal performance (Pratt and Haynes, 1950). Since then, it has been found that three syndromes are associated with tall fescue toxicosis (Stuedemann and Hoveland, 1988). In the upper South, cattle (Bos taurus spp.) signs include elevated respiration rate and gangrene resulting in loss of hooves, tails, and ears. This syndrome, known as fescue foot, was first described by Cunningham (1949) in New Zealand and occurred more frequently during winter. Second, where high rates of N fertilizer are applied to tall fescue pastures, hard fat accumulates along the bovine intestinal tract, resulting in upset digestion and difficult births (Bush et al., 1979; Stuedemann et al., 1975); this syndrome has been called fat necrosis. The third syndrome has general signs of failure to shed the winter haircoat, high respiration rates, intolerance to heat, poor animal gains, reduced milk production, depressed feed intake, and low conception rates (Hoveland et al., 1983; Stuedemann and Hoveland, 1988). These signs are most severe in warm weather and are collectively referred to as summer syndrome. The problems are serious, with cattle losses widespread throughout the tall fescue area. Beef cattle losses in the United States have been estimated at well over $600 million annually from reduced calf births and lower weaning weights (Hoveland, 1993). In addition, pregnant mares (Equus caballus) that graze endophyte infected (E+) tall fescue during the last weeks before parturition suffer from agalactia and may deliver dead foals or foals that die soon after birth. Losses from such incidents have not been calculated, but they can be severe in the case of valuable animals.

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