Environmental Heat Exposure on Cattle Plasma Catecholamine and Glucocorticoids

Abstract

Nonlactating Holstein cows were exposed for varying times to environmental heat to determine changes in plasma epinephrine, norepinephrine, and glucocorticoids (principally hydrocortisone). Short heat exposures of 40 to 43 C caused average increases of 45 and 4270 in epinephrine and norepinephrine at 1 hour. Maximal increases (at 4.5 hours) of 127 and 847o were observed for epinephrine and norepinephrine. Glucocorticoids increased 3870 at I hour and declined to the control at 4.5 hours. More moderate 3-day exposure to 35 C increased epinephrine 70% at 6 hours and norepinephrine 3570 at 2 hours, which persisted throughout the 72-hour exposure. Glucocorticoids increased 62g by the second hour of exposure, reached a peak of 12070 at 4 hours, then declined gradually to values not different from normal at 48 hours and remained at this level for duration of exposure.