Lamb mortality, birthweight, and nutrition in late pregnancy

Abstract

Abstract Mortality data on 5163 Romney × Suffolk lambs were collected at Winchmore Irrigation Research Station from 1976 to 1981. Mortality from birth to tailing (25 days) for single, twin, and triplet births was 14.1, 14.7, and 33.0% with mean birth weights of 5.2, 4.1, and 3.3 kg respectively. Ninety-four percent of all deaths occurred within 72 h of birth. Dystocia accounted for 50.4% of all single deaths and starvation/exposure for 45.0% of all multiple deaths. The proportion of ewes assisted at lambing increased with birthweight above 4.5 kg to reach almost 19 and 8% for single and twin births respectively. If lambs that were assisted at birth, but survived to weaning, are regarded as potential deaths, the overall potential mortality of single and twin lambs was 27.9 and 20.2% respectively. Ewe liveweight gain during the last 6 weeks of pregnancy was associated with increased birthweights of single and twin lambs (P < 0.05). A liveweight change of approximately 10 kg in ewes was required to alter birthweight by 0.5 kg in both single and twin lambs. Single lamb mortality was not significantly affected by live-weight gain or ewe liveweight at lambing on either a between-mob or a within-mob basis. This suggests that with single bearing ewes it may be more economical to save feed for lactation when feed requirements of ewes are high, rather than to offer it in late pregnancy. However, when multiple bearing ewes were offered additional feed in late pregnancy to increase liveweight, lamb mortality was reduced, suggesting merit in improved pre-lamb feeding for these ewes.