Tall fescue is the most important cool-season pasture species in the transition zone of the southeastern U.S.A., occupying more than 10 million hectares. Forage quality indices such as crude protein, in uitro digestibility etc. Indicate that tall fescue should be capable of stimulating high animal performance. Nevertheless since its widespread introduction in the early 1950's, tall fescue has been associated with a myriad of animal production problems. Recently researchers have been able to associate poor animal performance with an endophytic fungus present in the plant tissue of tall fescue. The history and current situation in the U.S. with respect to the endophyte of tall fescue and its influence on economic animal production are discussed. Keywords: Tall fescue toxicity, endophyte, Summer Syndrome, ocremonium coenophialum.
