Changes in the cortisol responses of lambs to tail docking, castration and ACTH injection during the first seven days after birth

Cortisol responses of Dorset and Scottish Blackface lambs were investigated at six ages between birth and seven days. There were four treatments: control handling and blood sampling (n = 52), tail docking (T) (n = 57), castration plus tail docking (CT) (n = 54), and intravenous adrenocorticotrophin (ACTH) injection (n = 60). Most lambs exhibited transient rises in plasma cortisol concentrations after treatment and the results in individuals were expressed as the area under the cortisol curve (integrated response). Postnatal changes in the integrated responses of control, T and CT lambs differed significantly between the two breeds; in Dorsets they increased markedly between four hours and one day and then decreased, whereas in Scottish Blackface lambs there were no significant changes. The cortisol responses of ACTH lambs decreased markedly between four hours and seven days in both breeds. The results shed light on postnatal changes in the activity of the hypothalamic-pituitary-adrenal axis and suggest for both breeds that the average increments in ACTH secretion caused by noxious stimuli increased markedly during the first one to three days after birth. Whether this reflected parallel increases in the levels of distress experienced by the lambs remains to be clarified.