Effect of slope of lambing site on lambs slipping and lamb mortality

Two experiments were carried out to determine the effect of slope on lamb mortality. In Experiment 1, 166 Marshall Romney (MR), 170 conventional Romney (CR), and 59 MR X CR ewes were allocated to one of 17 lambing areas of 0.2-0.4 ha and uniform slope. Mean slopes ranged from 3 to 440 and each area was surrounded by electric netting fences. Ewes entered their respective lambing areas 2 days before the expected lambing date and remained there for 4-5 days. In Experiment 2, two 1 ha plots selected on the basis of conformity of slope (36-44°) and 100-120 m long were each divided into three equal lambing areas by fences down the slope. Barriers either 15 or 30 m apart were constructed of 33-cm-high woven polyethylene mesh across the slope on two of the three lam bing areas in both plots. Lamb mortality in Experiment 1 was not affected by slopes up to 300 but there was a large increase in lamb mortality with slopes of 36-44° (19.4% lamb mortality for less than 300 versus 50.1% lamb mortality for more than 300 ). In Experiment 2, 83-90% of lambs slipped off the birth site and 68-70% of ewes followed their lambs down the slope. The barriers stopped only 60% of the lambs encountering them. The other 40% passed under or over the barriers. Barriers increased separation of twin lambs (39% no barriers versus 65% barriers). The incidence of ewes rearing both twins when the co-twins were separated soon after birth by 0-1 m, 2-4 m ,or greater than 4 m was 15/16, 1/5, and 0/18, respectively. MR ewes had a lower lamb mortality than CR ewes (17 versus 43%). Although there were no differences in the incidence of lambs slipping off the birth site (83% MR versus 89% CR), the MR ewes had a lower incidence of abandonment of lambs (20% MR versus 41% CR).