Effects of repeated changes in group composition on immune response, behaviour, adrenal activity and liveweight gain in farmed red deer yearlings

The validity of antibody and lymphocyte response as measures of social stress in farmed red deer hinds was assessed by comparison with other indices of stress. Ten 'wild' red deer (mixed, M), born to wild hinds post-capture, were each housed in separate groups of five farmed deer. After 2 weeks the groups were completely re-mixed. Mixing was repeated at weekly intervals for 4 successive weeks. As a control, ten 'wild' deer (C) were maintained in the same two groups of five throughout the study. All wild deer were immunised with keyhole limpet haemocyanin (KLH) 1 week prior to remixing (week 2). Mixed deer were subjected to more aggression than C deer (P < 0.001). At week 6, plasma cortisol concentrations after ACTH injection increased more in M than C deer (P < 0.05). Lymphocyte responses to KLH were significantly lower in M than C deer (P < 0.05), but there were no differences in antibody response to KLH. It is concluded that the repeated mixing of groups was a significant social stressor and that lymphocyte response to an antigen may be a more sensitive immunological measure of social stress in red deer than antibody response.