Mid-pregnancy shearing can increase birthweight and survival to weaning of multiple-born lambs under commercial conditions

Abstract

In several field studies, mid-pregnancy shearing has increased lamb birthweight, which may be associated with an increase in lamb survival. However, animal numbers have been too low in these studies to accurately examine any effects on survival rates to weaning. This study was designed to investigate the effect of mid-pregnancy shearing on the birthweight of multiple-born lambs and their survival rates to weaning under commercial farming conditions at 2 different sites. At Riverside, 657 twin- and 47 triplet-bearing ewes were either shorn at mid-pregnancy (n = 347) or left unshorn (n = 357). Similarly, at Tuapaka, 532 twin-, and 60 triplet-bearing ewes were either shorn at mid-pregnancy (n = 291) or left unshorn (n = 301). Mid-pregnancy shearing significantly (P<0.05) increased the birthweights of lambs at each site (by 0.44 and 0.13 kg at Riverside and Tuapaka, respectively). Mid-pregnancy shearing significantly (P<0.05) increased lamb weaning weights (by 1.07 kg) and survival rates to weaning (by 5.5%) at Riverside, but not at Tuapaka. These findings show that mid-pregnancy shearing under commercial farming conditions can increase the birthweight of multiple-born lambs and, when the birthweight response is large enough to reduce the numbers of otherwise lightweight lambs, it is associated with an increase in survival rates to weaning.