Short- and long-term effects of weaning on adrenocortical and functional response of lambs

Background: Weaning period is considered a crucial event in the management of ewes and lambs, resulting in a number of signifi cant challenges. Although multiple stresses signifi cantly affected adaptative capability of ewes in terms of changes in physiological mechanisms insuffi cient knowledges are available to understand the adrenocortical and functional responses of lambs to adapt to weaning stress. The main objective of the present study was to evaluate the effect of weaning associated with maternal separation on circulating cortisol concentrations, respiratory rate and rectal temperature changes after the fi rst 24 h weaning period and 2 weeks later in cross-bred lambs. Materials, Methods & Results: Thirty-four cross-bred lambs were assigned randomly to two treatments: 17 (unstressed control group) were housed in standard farming conditions with their mothers and 17 lambs (treated group) were submitted to weaning and separation from maternal care. Both groups were studied and sampled 2 weeks before (weaning) in baseline conditions (T0), 24 h (T1) and 2 weeks (T2) after (weaning). In treated group lambs showed decreases of cortisol concentrations 24 h after (P < 0.001) and 2 weeks after (P < 0.05) weaning, compared to baseline values. Weaning effects were shown for cortisol changes (P < 0.0001) in treated lambs. The comparison between control and treated lambs showed lower cortisol concentration both 24 h after weaning (P < 0.001) and 2 weeks later (P < 0.05) in treated than control subjects. Treated lambs showed decreases of respiratory rate 24 h after (P < 0.01) and 2 weeks after (P < 0.05), compared to baseline values, with a signifi cant weaning effects for RR changes (P < 0.001). No signifi cant changes were observed for RT at different times in treated lambs. Negative and signifi cant correlations were observed between RR and RT (r= -0.674; P < 0.05) for all measurement periods in control group. Discussion: Results obtained showed that the ability of the adrenocortical gland to modulate cortisol concentrations was different in control and treated groups. In fact, this ability remained unmodifi ed in unstressed animals, but signifi cantly decreased in weaned lambs. We conclude that the presence of maternal care did not appear to infl uence cortisol concentrations, as confi rmed by no signifi cant cortisol changes observed at T0, T1 and T2 in unstressed control lambs. The general higher no signifi cant RT values of control group than treated group would be in agreement with results observed in suckling lambs, with increased heat production, and could explain the existence of negative correlation between RR and RT only in control group. The decreases of cortisol concentrations after weaning were the evident effect of persistent stress suffered by lambs both early and late phases of weaning. These results showed that short- and long-term perturbations of the postweaning has measurable effects on adrenocortical and functional response of weaned lambs. These fi ndings suggest that circulating cortisol concentrations and RR values of lambs play an important role in providing additional information for comparative evaluation of weaning effects and related coping responses in small ruminants. Data obtained indicate that both the short- and long-term effects of weaning and maternal separation may be perceived as stressful and aversive stimuli.