Factors that influence mortality amongst lambs in the Elsenburg Dormer and SA Mutton Merino flocks.

Data related to 1 852 SA Mutton Merino and Dormer lambs born in the Elsenburg flocks, during the period 1978 – 1981 inclusive, were analysed by least squares procedures. The lambs were classified within years and breeds in an intensive group which was housed and constantly supervised during lambing, and an extensive group, where the lambing was supervised three times daily. Pre-weaning mortality amongst SA Mutton Merino lambs was significantly (P ≤0,05) higher than amongst Dormer lambs, primarily owing to significantly (P≤0,01) higher mortality which occurred during birth. Mortality during the period 1 to 3 days after birth was significantly (P≤ 0,05) decreased by intensive management. However, the contribution of this parameter to the reduction of the number of deaths to weaning was relatively small, resulting in a comparatively small benefit derived from intensive management. The pre-weaning mortality amongst SA Mutton Merino and Dormer lambs was nevertheless, significantly (P≤0,05) decreased from 23,3 and 20,6 to 20,4 and 14,6% respectively. Pre-weaning mortality amongst triplets in both breeds was double that amongst twins and singles. The highest rate of mortality tended to occur amongst the lighter lambs in both breeds, whereas the mortality rate amongst the heavier SA Mutton Merino lambs also tended to increase. Mortality amongst lambs born to SA Mutton Merino ewes of 7 years and older was significantly (P≤0,01) higher than in other ewe age groups.