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Physiological Responses of Cattle Consuming Tall Fescue to Environmental Temperature and Supplemental Phenothiazine¹

University of Kentucky, Lexington 40546-0215

Abstract

The influence of supplemental phenothiazine (P) on growth and physiological criteria was studied in parasite-controlled calves consuming endophyte (Acremonium coenophialum)-infected tall fescue (TF). In Exp. 1, nine Angus heifer calves (312 kg) were supplemented with 227 g corn-mineral (CM) mix twice daily and allowed ad libitum access to either high-endophyte (HE) G1-307 (>90% infected) or low-endophyte (LE) Kenhy (<1% infected) tall fescue hay, or HE G1-307 plus 2 g/d P in the daily supplement. Calves were kept in temperature-controlled rooms for 12 d at 21°C followed by 7 d at 34°C. In Exp. 2, 48 Angus steer calves (312 kg) were assigned to treatment groups consisting of calves grazing HE Kentucky-31 (57% infected) or LE Johnstone (<1% infected) TF, and supplemented daily with either .91 kg of a control CM mix or .91 kg of the CM mix containing 2 g P. The 112-d experiment was initiated on May 4 with BW and rectal temperature (RT) measurements and blood collected at 28-d intervals. In both experiments, calves receiving HE TF had lower (P < .01) serum prolactin concentrations (PRL) at elevated ambient temperature and lower (P < .01) serum alkaline phosphatase activities (AP) but higher (P < .01) RT than calves consuming LE TF regardless of ambient temperature. In Exp. 1, PRL and AP were not affected (P > .15) by P. In Exp. 2, daily gain through 112 d was lower (P < .01) for calves grazing HE than for those grazing LE TF (.66 vs .91 kg/d) but was not affected (P > .15) by P. No interaction of P and endophyte level was detected. Calves fed P in Exp. 2 had higher AP (P < .01) and PRL (P < .12) than control calves. These data indicate that P may reduce HE-associated depression of PRL and AP in cattle grazing TF; however, the magnitude of these reductions may depend partially on ambient temperature, with less effect at an elevated temperature.

¹ This paper (No. 88-5-86) is published with the approval of the Director of the Kentucky Agric. Exp. Sta.

² Dept. of Anim. Sci.

³ ICI Americas, Inc., Chem. Div., Wilmington, DE.