Calves' responses to repeated social regrouping and relocation

Because of welfare concerns and increased labor efficiency, calves are incr easingly housed in groups. To reduce variability in live weight within grou ps, farmers frequently regroup calves according to growth rate. We assessed the consequences of repeated regrouping and relocation on the welfare of 3 2 male Holstein calves housed in pairs. Animals of half of the pairs (regro uped calves) were placed in a new pen with a new partner once a week for 14 wk. Animals of the other half of the pairs (control calves) stayed in the same pen with the same partner. Behavior was observed for the 3 h following four mixings and for 24 h after all relocations were finished. The functio ning of the hypothalamic-pituitary-adrenal axis and of the sympathetic nerv ous system were assessed. Calves were weighed once a week, their health was assessed daily, and abomasa were inspected when the calves were slaughtere d. Calves reacted to the first mixing by interacting with the new partner a nd increasing their general activity (sniffing the partner in regrouped cal ves vs controls: 5.5 vs 2.9, P < 0.01; percentage time stepping: 3.2 vs 1.3 , P < 0.001). This effect disappeared by the ninth mixing. After all reloca tions were completed, regrouped calves were more active at the end of the d ay and less active at night (P < 0.05). Cortisol responses to exogenous ACT H were higher in regrouped calves (integrated response: 6,688 vs 5,508 ng.m in/mL, P < 0.01). Basal cortisol levels, ACTH responses to corticotropin-re leasing hormone, activities of catecholamine-synthesizing enzymes (tyrosine hydroxylase and phenylethanolamine N-methyl transferase), and the incidenc e of health problems and growth rates did not differ between the two groups . Regrouped calves had fewer abomasal ulcers. Apart from the increased sens itivity of the adrenal cortex of regrouped calves to ACTH and the modificat ion in the daily rhythm of activity, there was no clear evidence that repea ted regrouping and relocation stresses calves. Aggression between calves wa s rare, and calves seemed to habituate to repeated mixing.