Effect of consuming fungus-infected and fungus-free tall fescue and ergotamine tartrate on selected physiological variables of cattle in environmentally controlled conditions.

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)