Tall fescue (Festuca arundinacea) is a cool-season grass widely used as pasture and hay for livestock in the southeastern USA. Fescue toxicosis, a condition that alters beef cattle grazing behavior and reduces growth and reproductive performance in ruminant livestock, has been associated with consumption of ergot alkaloids produced in wild-type endophyte-infected (EI) tall fescue. Most tall fescue in improved USA grasslands is EI, and the economic losses from fescue toxicosis are estimated to exceed $600 million annually in the USA beef industry alone. Endophyte-free (EF) tall fescue is an alternative to EI tall fescue that provides good animal performance, however, endophyte-based plant persistence advantages are sacrificed. Nil ergot alkaloid producing endophyte-infected (AR542, AR502) tall fescue has potential for capitalizing on both good animal performance and enhanced plant persistence. A 3-yr grazing trial conducted with lambs in central Georgia indicated that fescue toxicosis is alleviated by incorporating AR542 and AR502 endophytes into tall fescue pastures. A similar study was conducted for 2-yr with stocker cattle in central Georgia and northwest Georgia. In both the lamb and stocker cattle trials, animal average daily gain was higher in livestock grazing AR542, AR502, and EF pastures over animals grazing EI pastures. Depressed serum prolactin levels and elevated rectal temperatures, indicative of fescue toxicosis, were observed in animals grazing EI tall fescue but not in animals grazing AR542, AR502, and EF tall fescue. A third experiment examined steer grazing behavior on AR542, EF, and EI tall fescue pastures. Steers grazing AR542 and EF tall fescue spent more time grazing, took more bites, and had higher forage intake than steers grazing EI tall fescue. This helps explain differences in average daily gain. Additionally, steers grazing EI pastures spent more time standing and used more water than cattle on AR542 and EF pastures, possibly in an attempt to cope with heat stress associated with fescue toxicosis. Steer grazing behavior on AR542 and EF pastures favored superior growth performance over cattle grazing EI tall fescue. Nil ergot alkaloid producing endophyte technology provides cattle growth advantages on tall fescue pastures.