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.

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Two experiments were conducted to determine the physiological responses of consuming a fungus-free (FF) or fungus-infected (INF) tall fescue diet (Exp. 1) or the FF diet plus ergotamine tartrate at 30 ppm (FF/ET, Exp. 2) in a thermoneutral (21 degrees C) or heat-stressed environment (32 degrees C, dry bulb; 10 degrees C dew point). Treatment periods lasted 28 d after a 10-d adaptation period. Experiment 1 was replicated three times, and Exp. 2 was replicated twice, with eight Holstein steers in each replicate (mean BW = 185 kg). Feed intake (FI), rectal temperature (RT), and respiration rate (RR) were recorded daily, and heart rate (HR) and infrared temperatures at the ear canal (ECT), ear tip (ETT), pastern (PT), coronary band (CBT), and tail tip (TTT) were recorded weekly. Consumption of INF and FF/ET compared with FF diets decreased (P less than .10) FI, HR, ECT, PT, CBT, and TTT and elevated (P less than .10) RT and RR by 2.8, 2.77 kg/d; 17, 23 beats/min; .8, 1.1 degrees C; .9, 1.1 degrees C; .8, .9 degrees C; 1.1, 2.6 degrees C; .3, .5 degrees C; and 8, 8 breaths/min; respectively. Ear-tip temperature was reduced (P less than .10) 1.6 degrees C by consumption of INF but not by consumption of FF/ET. Reduction of peripheral temperatures is indicative of reduced blood flow to peripheral areas as a result of vasoconstriction.(ABSTRACT TRUNCATED AT 250 WORDS)

Previous research has implicated an endophytic fungus as being associated with fescue toxicity (summer syndrome) in cattle grazing Kentucky 31 tall fescue (Festuca arundinacea Schreb.) pastures. Hay and seed were harvested from Kentucky 31 pastures known to be either fungus-free or heavily infested with an endophytic fungus identified as Acremonium coenophialum Morgan-Jones and Gams. Four diets containing either 60% fungus-free seed, 60% fungus-infested seed, 85% fungus-free hay or 85% fungus-infested hay were group-fed to three steers each (avg wt 239 kg) in a 53-d feeding trial. Presence of the fungus reduced (P less than .05) daily gains (kg/d) in steers fed either the seed diets (.96 vs .20) or the hay diets (.66 vs .28). Feed intake was depressed 36% for the seed diets and 8% for the hay diets when the fungus was present. Rectal temperatures were elevated .6 C (P less than .05) for both groups receiving diets containing the fungus, but respiration rate was elevated only in the fungus-infested seed group. In vitro dry matter disappearance was not decreased by presence of the fungus. Steers receiving fungus from either seed or hay were nervous and highly excitable, which resulted in large variations in plasma epinephrine and norepinephrine concentrations. The results of this experiment further implicate an endophytic fungus as being associated with fescue toxicity.