Plasma cortisol and total progestin levels in Holstein steers during acute exposure to high environmental temperature (42 C) conditions.

Plasma cortisol concentration as estimated by CPB radioassay increased significantly in cattle during 4 hr of acute thermal exposure while plasma progestins did not. Changes in plasma cortisol were gradual with the onset of heat exposure and correlated significantly with rectal and environmental temperatures although the correlation was greater with rectal temperature. However, the rise and decline in plasma cortisol levels following, respectively, the onset and cessation of thermal exposure preceded changes in body temperature. Adrenocortical function in steers and the possible significance of plasma cortisol secretion during acute thermal stress are discussed. (