Adrenal responses of Angus x Hereford cattle to the stress of weaning.

To test adrenal responsiveness of beef cattle to stress, plasma norepinephrine, epinephrine, and cortisol responses of Angus x Hereford cattle to weaning were measured in blood samples taken from 1) eight cows and their 4- to 6-mo-old calves before and after separation and, the following day, before and after being reunited and 2) an equal number of control animals. After separation and before they were reunited, dams were returned to their original pen and calves to an adjacent pen. Experimental trials were conducted every 2 wk and included two cow/calf pairs per trial. Norepinephrine concentrations tended to increase in calves after separation, were increased (+82 pg/mL, P < .01) on the 2nd d before animals were reunited, and decreased (-88 pg/mL, P < .01) after animals were reunited. Epinephrine concentrations tended to increase in calves after separation, were increased in calves (+128 pg/mL, P < .001) and dams (+104 pg/mL, P < .001) on the 2nd d before animals were reunited, and decreased after calves (-162 pg/mL, P < .001) and dams (-101 pg/ml, P < .001) were reunited. There were no significant effects of time on catecholamine concentrations for control animals. Cortisol concentrations for treated and control animals tended to increase in sequential samples each day; however, the increases were small (approximately 1 ng/mL) and concentrations remained low (> 5 ng/mL). In conclusion, peripheral catecholamine concentrations in beef calves and epinephrine concentrations in dams increased in response to stress associated with weaning and separation.(ABSTRACT TRUNCATED AT 250 WORDS)