Ms. Cockram et al., THE BEHAVIORAL, ENDOCRINE AND LEUKOCYTE RESPONSE OF EWES TO REPEATED REMOVAL OF LAMBS BEFORE THE AGE OF NATURAL WEANING, Applied animal behaviour science, 38(2), 1993, pp. 127-142
Changes in the blood leucocyte population in response to psychological
stressors could increase susceptibility to disease and be useful in t
he assessment of animal welfare. This paper examines the effect of rep
eated lamb removal on the blood leucocyte population of ewes and quant
ifies 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 grou
p 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 bac
k 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 con
tinuously for the 24-day experimental period. The removal of lambs pro
duced behavioural changes in the ewes. These included: orientation tow
ards the lamb, vocalization, raised head, erect ears, and decreased ly
ing 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 beta-endorphin res
ponse on Day 1 of lamb removal, but the mean responses were not statis
tically different from the control group. There was no obvious plasma
prolactin response to the treatment. On Day 10 of lamb removal, the bl
ood concentration of neutrophils in the treatment ewes had increased a
nd the proportion of CD2 lymphocytes and T19 lymphocytes had decreased
compared with that of control ewes. There were no significant differe
nces 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 remov
al. However, this stressor had no significant effect on the endocrine
and immune measurements studied.