Steer Performance and Association of Acremonium coenophialum Fungal Endophyte on Tall Fescue Pasture1

Abstract Poor animal performance on tall fescue (Festuca arundinacea Schreb.) pasture may be associated with toxic products produced by the fungal endophyte Acremonium coenophialum Morgan‐Jones and Gams (previously identified and referred to as Epichloe typhina (Fries) Tulasne). The object of this study was to determine steer performance on ‘Kentucky 31’ tall fescue pastures which were either heavily infested or relatively free of the fungal endophyte. Replicated 1.2 ha paddocks were located in west central Alabama on three soils, Sumter clay (fine silty, carbonatic, thermic Rendolic Eutrochrept), Houston clay (very fine montmorillonitic, thermic Typic Chromudert), and Eutaw clay (very fine, montmorillonitic, thermic Entic Pelluderts). They were fertilized annually with 224 kg N ha−1 and grazed with yearling steers. The grazing season during the 4‐year period averaged from 23 October to 24 December and 26 February to 16 June. Tall fescue, averaging 94% of plants fungus infested, produced 768 animal days ha−1 and produced 384 kg beef ha−1 with an average daily gain (ADG) of 0.50 kg. Tall fescue with less than 5% of plants infested produced 593 animal days ha−1 and produced 492 kg beef ha−1, with an ADG of 0.83 kg. Rectal temperatures were 0.8 °C higher and hair coats much rougher on steers which grazed fungus‐infected grass rather than grass free of the fungus. Results of the study furnish further evidence that the fungal endophyte, A. coenophialum, is associated with low performance of steers on tall fescue pasture. In the absence of the fungal endophyte, ADG of steers on tall fescue is high and similar to that on small grain pastures.