The behavioural, endocrine and leucocyte response of ewes to repeated removal of lambs before the age of natural weaning

Abstract

Changes in the blood leucocyte population in response to psychological stressors could increase susceptibility to disease and be useful in the assessment of animal welfare. This paper examines the effect of repeated lamb removal on the blood leucocyte population of ewes and quantifies the behavioural and endocrine responses to the stressor. Twelve ewes which had given birth to twins, were placed in separate pens with their lambs. After 13 days, the lambs (14–19 days old) from one group of six ewes (treatment group) were removed from the pens and placed in a pen 11 m from the nearest ewe. After 3 h the lambs were moved back to their dam. The lambs then remained with their dam for 3 h before being removed for a second period of 3 h. This procedure was repeated for 23 days. A control group of six ewes remained with their lambs continuously for the 24-day experimental period. The removal of lambs produced behavioural changes in the ewes. These included: orientation towards the lamb, vocalization, raised head, erect ears, and decreased lying and sleeping behaviours. Although these changes were present over the 24-day experimental period, there were signs of habituation after 3 days of the treatment. The endocrine responses to lamb removal were less marked. Some ewes showed a plasma cortisol and β-endorphin response on Day 1 of lamb removal, but the mean responses were not statistically different from the control group. There was no obvious plasma prolactin response to the treatment. On Day 10 of lamb removal, the blood concentration of neutrophils in the treatment ewes had increased and the proportion of CD2 lymphocytes and T19 lymphocytes had decreased compared with that of control ewes. There were no significant differences between the treatment and control ewes in either the delayed type hypersensitivity skin responses to Dinitroflurobenzene or the humoral antibody responses to ovalbumin. These results indicate that ewes can show behavioural responses to a stressor, such as repeated lamb removal. However, this stressor had no significant effect on the endocrine and immune measurements studied.