Tall Fescue Toxicity

Tall fescue (Festuca arundinacea Schreb.) has become the predominant cool-season pasture grass in the southeastern United States. Dry matter yields of tall fescue are excellent, and the chemical composition used to determine forage quality is equal to that of other cool-season pasture grasses. However, animal performance on tall fescue has not been consistently satisfactory. Fescue foot, fat necrosis, and poor performance are the three major animal problems associated with tall fescue pastures. Fescue foot occurs sporadically, affects a very small portion of the animals grazing tall fescue, and is probably caused by mycotoxins. Fat necrosis in cattle has been associated with tall fescue pastures receiving high levels of plant nutrients from chicken litter. Fat lesion will disappear when the animals are removed from the pastures. Poor animal performance usually occurs during late summer but does not occur every year or with equal severity. This condition affects a large portion of the cattle grazing tall fescue but is not an acute condition like fesuce foot or fat necrosis. The poor performance parallels the accumulation of alkaloids in tall fescue during the growing season. Perloline inhibits in vitro ruminal cellulose digestion, fatty acid production, and growth of rumen cellulolytic bacteria. It is hypothesized that the alkaloids inhibit rate of digestion in the rumen and subsequently, the rate of passage through the animal decreases, thereby decreasing energy and nutrient availability to the animal.