Abstract
In evaluating stress in farm animals, it would be useful to know whether there were consistent endocrine responses that could be followed. Adrenal cortisol secretion is quite variable, but β-endorphin secretion and adrenal progesterone production may be useful indicators of stress. Changes in plasma concentrations of cortisol, β-endorphin and progesterone were studied in spring-born, castrated male calves (steers) (6 mo of age ± 18 d, 516 ± 26 kg, n = 12) subjected to the stress of routine dehorning. Steers were isolated from their dams for 2 h before headgate restraint (control) or restraint and dehorning. They were bled 60 and 10 min prior to headgate restraint or restraint and dehorning. Blood samples were also collected immediately after headgate restraint or restraint and dehorning (time 0) and 5, 10, 30 and 60 min later. All blood samples were taken from a jugular catheter, and the blood sampling that was done out of the headgate involved minimal manual restraint. Plasma β-endorphin concentrations were similar in control steers and dehorned steers (P > 0.05) and decreased significantly following restraint or restraint and dehorning (P < 0.05). Plasma cortisol concentrations rose significantly 5 min after dehorning and were elevated for 60 min; but with restraint only, plasma cortisol concentrations rose to a peak 5 min after release from chute restraint and then declined (P < 0.05). Plasma cortisol concentrations were greater in dehorned steers than in control steers in the period from 10 min after dehorning or headgate restraint to 60 min after headgate restraint (P < 0.0043). Plasma progesterone concentrations rose to a peak 10 min after dehorning and then declined, but in control steers, a peak was seen at 5 min after release from restraint (P < 0.05). Plasma progesterone concentrations were greater in dehorned steers between 5 and 60 min after dehorning than in control steers (P < 0.05). From these data, we concluded that in prepubertal, castrated male calves, β-endorphin was not released in any significant quantities in response to the stress of dehorning. In steers, adrenal cortisol and progesterone were secreted in response to acute stress, and a ratio of the two may provide a useful assessment of stress; this requires further study. Key words: Cortisol, progesterone, β-endorphin, stress, calves
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