Effect of Milk Source on Welfare and Weight Gain of Lambs
The possibility of lessening the adverse welfare impact of artificial rearing was assessed in thirty Comisana lambs under conditions of ad libitum feeding. The lambs were assigned to a control dam-suckled group (DS) or to one of two test groups, each consisting of 10 animals. 18–24h after parturition, test lambs were separated from their dams: during the first post-separation week 10 subjects (EM) were offered ewe milk and the other 10 (MX) a 50:50 mix of ewe milk and a milk substitute. An artificial feeding system, to which the test lambs had free access, was filled with milk twice daily. After the first week, a transition from EM or MX to 100 per cent (reconstituted) milk substitute was carried out over 3 days in both test groups, gradually reducing the proportion of ewe's milk. In vivo cell-mediated immune response of lambs to phytohemagglutinin percutaneous injection were evaluated at 5, 15 and 25 days of age. At 10 and 20 days of age, all lambs were subjected to 15min isolation tests, during which latency to move, duration of movement and number of bleats were recorded. Blood samples were collected immediately before the test and 15 and 60min after, in order to assess the effect of differential rearing on the cortisol response of animals at different ages. In addition, the weight gain of lambs was recorded during the first 35 days of age at weekly intervals. Latency to move and duration of movement were not significantly affected by the experimental treatment, whereas the number of bleats was higher (P < 0.001) in dam-suckled lambs compared to test lambs at both 10 and 20 days of age. Neither immune response nor cortisol levels were affected by milk source. Although weight gain increased with increasing amounts of ewe's milk in the diet, the overall differences between the three groups were small and not significant. These findings suggest that the provision of ewe milk or a mix of ewe milk and a milk substitute during the first post-separation week can be a suitable strategy to sustain the welfare and production performance in the artificially reared lamb.
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