Effects of husbandry on immune function in farmed red deer and their implications for stress
In experiment 1, groups of wild (W) and farmed (F) weaned calves were maintained at either high (H) or low housing (L) density. W calves had lower antibody titres and lower lymphocyte responses to antigen than F calves (P<0.05). At the start of the study, W and H calves exhibited a greater plasma cortisol response to ACTH than F and L calves, respectively (P<0.05), but thereafter there were no significant differences. Wild calves were less active than F calves (P<0.01) and WH calves were the most aggressive (P<0.1). In experiment 2, individual wild yearlings were grouped with farmed yearlings. Groups were remixed every week, for 4 weeks. The incidence of agnostic behaviour was greater in mixed deer than in the control deer, maintained in the same groups throughout the study (P<0.001). At the end of the study, mixed yearlings had greater plasma cortisol responses to ACTH than control deer (P<0.05). Lymphocyte response to antigen was lower in mixed than controls (P<0.05), but there were no differences in antibody response. In experiment 3, groups of weaned calves were subjected to either aversive (AV) or non-aversive (NAV) handling treatments. Lymphocyte responses to antigen tended to be lower in AV than NAV calves (P<0.05). After three weeks, AV had greater plasma cortisol responses to ACTH than NAV calves (P<0.05), but treatment had no measurable effect on fearfulness. In experiment 4, weaned calves were housed either individually (ISO) or in groups (GP). ISO were less active (P<0.001) than GP calves. Antibody and lymphocyte responses to antigen were greater (P<0.05) in ISO than GP calves. Overall, stressors associated with group-housing consistently lowered lymphocyte response to antigen, but antibody responses were less consistent. Differences in immune responses corresponded to changes in behaviour, but not productivity or cortisol response. It is concluded that social stress had a greater impact on immune function than social isolation and aversive handling.