Performance of cows and calves grazing endophyte infested fescue pasture

Angus X Hereford cows (Bos taurus L.) with spring born Simmental sired calves grazed year round for three years on eight ‘Kentucky 31' tall fescue (Festuca arundinacea Schreb.) pastures at the Highland Rim Experiment Station near Springfield, Tennessee. Individual pastures contained 0 to 86% plants infected with Acremonium coenophialum Morgan-Jones and Gams. The objective of the study was to evaluate effects of increasing endophyte infestation percentage on cow-calf performance. For statistical analysis, pasture infestation percentages were classified into three groups: Low (EL) (<5% infested), intermediate (EI) (40 to 65%), and high (EH) (>80%). Cows grazing EL pastures had higher pregnancy and calving rates (80 and 78%, respectively) than cows grazing El pastures (56 and 49%, respectively) and cows grazing EH pastures (56 and 49%, respectively). There were no year effects on cow reproductive efficiency, milk production, serum prolactin concentration, or calf weaning weight. Mean cow serum prolactin concentrations of EL, El, and EH cows were 133, 39, and 38 ng/ml, respectively. Average daily gains (ADG) of EL, El, and EH calves during spring (April-June), summer (July-October), and total grazing season (April-October) were 2.32, 1.94, 2.23; 2.08, 1.18, 1.87; 2.06, 1.56, 1.90 lb, respectively. Adjusted 240-d weight for calves grazing EL, El, and EH pastures were 625, 537, and 543 lb, respectively. Increased endophyte percentages between 37% and 86% did not decrease cow or calf performance or physiological characteristics, except calf serum prolaction concentrations, more than that observed at 37% infestation. Calf serum prolactin concentrations continue to decrease as infestation percentages increase within this range. Changes in infestation percentages of EL and EH pastures were similar (12 percentage units change) during the three years, but infestation percentage of 3 out of the 4 El pastures increased 27 to 33 percentage units during the 3-yr study.