Effect of gradual transition from maternal to reconstituted milk on behavioural,endocrine and immune responses of lambs

The possibility of reducing the stress associated with artificial rearing through a gradual transition from maternal to reconstituted milk was assessed in thirty Comisana lambs. Animals were assigned to a control dam-suckled group (Suckled) and two test groups. Eighteen to twenty-four hours after parturition, test lambs were separated from their dams: 10 subjects were offered a commercial milk substitute (Sub), whereas the other ten (Mix) were subjected to a gradual transition from maternal to reconstituted milk over ten days. Test-lambs had free access to milk 3 h a day. In vivo cell-mediated immune response of lambs to phytohemagglutinin percutaneous injection was evaluated at 5, 15 and 25 days of age. At 10 and 20 days of age, all lambs were subjected to 15 min isolation tests, during which latency time to move, duration of movement and number of bleats were recorded. Blood samples were collected immediately before the test, 15 and 60 min after in order to assess the effect of differential rearing on cortisol response of animals at different ages. In addition, weight gains of all lambs and milk intakes of test lambs were recorded during the first 35 days of age at weekly intervals. Sub showed a lower immune response (P<0.01) and, at 10 days of age, increased levels of plasma cortisol (P<0.001) as well as a reduced duration of movement (P<0.001) and a longer latency time to move (P<0.001) compared to Suckled and Mix. There were no significant differences between Suckled and Mix for both immune, cortisol and behavioural responses. Mix lambs consumed more milk (P<0.006) and had higher weight gains (P<0.001) compared to Sub lambs. However, Mix lambs gained less weight on average (P<0.05) than Suckled lambs. Our results suggest that a gradual transition from maternal to reconstituted milk is effective in stimulating milk consumption and minimising the detrimental effects of artificial rearing on behavioural, endocrine and immune responses of lambs.