EFFECTS OF ENDOPHYTE-INFECTED TALL FESCUE ON ANIMAL PERFORMANCE

Cattle grazing tall fescue (Festuca arundinacea Schreb.) infected (E+) with the fungal endophyte Acremonium coenophialum (Morgan-Jones and Gams) or fed diets containing E+ hay and seed exhibit signs of toxicosis. These signs are intensified by a hot environment and include hyperthermia, poor appetite, rough hair coat, reduced pins, lowered conception rates, suppressed milk production and hypoprolactinemia. As a result of the hyperthermia, cattle seek shade and stand in water. Grazing times for cattle on E+ fescue change to the cooler evening and night hours compared with grazing times on endophyte-free (E-) fescue. Cattle switched from E- to E+ fescue exhibit changes in grazing times and decreased forage intake within days, whereas cattle switched from E+ to E- continue to exhibit signs of toxicosis for several weeks. In most fescue grazing studies where several levels of infestation were present, steer average daily gains (ADG) decreased linearly by approximately 0.045 kg for each 10% increase in E + level. The decrease in ADG due to E+ was numerically greater for British-bred (Bos taurus) steers than for Brahman-cross (Bos indicus) steers although statistical significance has not been consistent. Differences in ADG are associated more with decreased intake than other factors such as decreased digestibility, although in hay and seed feeding trials the decreased pin was greater than could be accounted for by the decreased energy consumption. Steers that graze E+ fescue prior to entering a feedlot for finishing probably will exhibit compensatory gains unless they enter the feedlot during a period of heat stress. Lactating beef cows grazing E+ pastures often will be in negative energy balance, have reduced pregnancy rates and have decreased milk production compared with those grazing E-. Calf weaning weights also will be reduced. For replacement heifers continually consuming fescue pasture or hay varying from 0 to 99% infested, milk production decreased 0.15 kg, pregnancy rate decreased 3.5% and ADG decreased 0.04 kg for each 10% increase in infestation level. Pregnant mares grazing E+ fescue have a prolonged gestation of approximately 1 month, fail to exhibit normal signs of approaching parturition, have a high incidence of dystocia, retained and thickened placentas, weak or stillborn foals, and aplactia, and decreased pregnancy rates. Energy supplementation of mares grazing E+ fescue has not been effective in ameliorating these reproductive problems. Removal of mares from E + fescue 1 month prior to anticipated parturition results in normal parturition and mammary development. Removal of mares 10 days post-term results in signs of impending parturition within 48 h. Fescue toxicosis signs have been observed in all species studied, and all have had some measure of animal performance adversely affected.