Progressive weaning alters behaviour and biomarkers of stress in weaned lambs subjected to social isolation

The mother-young contact during suckling influences the development of the offspring and their stress-coping abilities. Progressive weaning reduces the stress response in lambs as the separation time increases gradually until permanent maternal deprivation. The aim of this study was to determine if repeated maternal deprivation in suckling lambs alters their behavioural, physiological and immunological responses to social isolation after weaning. Twenty-four Saint Croix single born-lambs remained with their mothers for their first 29 days of age. Thereafter, 12 lambs were temporarily separated from their mothers every day for 4 weeks, during 4 h/d the first week, increasing 4 h weekly until they were separated 16 h/day (progressive weaning group: PW). During the progressive separation, PW lambs were moved to an enclosed pen, where they did not have visual or olfactive communication with their mothers. The other 12 lambs remained in permanent contact with their mothers until the definitive separation of both groups at 61 days old (abrupt weaning group: AW). At day 90 of age, all lambs were individually isolated for 10 min in a novel place, alternating one lamb from each group. Lambs’ behaviour was video recorded during the test. Cortisol concentration and haematological measurements were determined before and after the test. The PW lambs crossed more lines (P = 0.007), attempted to escape more times (P = 0.009), displayed more freezing behaviour (P = 0.01) and tended to vocalise more than AW lambs (P = 0.054). The AW lambs tended to sniff more times (P = 0.09) than the PW lambs. Cortisol concentration and the percentage of monocytes were lower in PW than in AW lambs (P ≤ 0.04). In conclusion, lambs repeatedly deprived of their mother displayed a more intensive behavioural response to social isolation one month after the definitive separation from their mothers. Progressive weaning reduced the cortisol concentration and the percentage of monocytes. These results call attention to the importance of further studies being undertaken in reference to the short and long-term effects of different procedures applied in order to better improve mother and the lamb welfare before artificial weaning.