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Abstract
This study compared beef steer performance on pastures of ‘AU Triumph’ tall fescue (Festuca arundinacea Schreb.) which were free of the fungal endophyte Acremonium coenophialum Morgan-Jones and Gams (previously identified and referred to as Epichloe typhina (Fries) Tulasne) with that on ‘Kentucky 31’ fescue having three levels of endophyte infection. Replicated 1.2 ha paddocks were located in west central Alabama. They were fertilised annually with 224 kg N ha-1 and grazed with yearling steers. The grazing season during the 3-year period averaged from 30 September to 26 December and from 24 February to 27 May. Endophyte infection levels were 0% on AU Triumph and 1, 34, and 90% on Kentucky 31. In general, stocking rate increased with higher fungus infection levels. Average daily gain (ADG) of the steers was shown to decline in a linear fashion with increasing A. coenophialum infection. Steer gain per ha did not react consistently among years. The greatest differences for gain per ha occurred during the 1982–83 grazing season. There, the response was clearly a linear decline in gain per ha with increasing fungus infection levels. A similar, quadratic response was shown for the 1981–1982 grazing season. No consistent differences were shown for ADG on AU Triumph and essentially fungus-free Kentucky 31 (1% infected). Where differences in stocking rate occurred for these two treatments, AU Triumph usually had the higher stocking rate. Although significant differences were shown between AU Triumph and the essentially fungus- free Kentucky 31 only during the 1982–83 season, the 3-year average gain per ha of AU Triumph was 12% higher than on the essentially fungus-free Kentucky 31.