The incidence of dystocia in fine-wool Merino ewes

The mean incidence of dystocia in 1,510 fine-wool Merino ewes over a ten-year period was 4.1% of ewes lambing. In the 10 year period, 10% of all neonatal mortality was attributed to dystocia and in only 23% of dystocias was lamb presentation abnormal. The incidence of dystocia was not related to age of ewe. Significantly more ewes experienced dystocia at spring than winter (P less than 0.05) or summer (P less than 0.01) lambings. The mean birth weights of dystocic single and twin born lambs were 4.19 and 3.38 kg respectively. The corresponding birth weights of lambs that did not experience dystocia were 3.69 and 3.00 kg. More ewes experienced dystocia when stocked at 12 or 16 per ha than at 8 per ha (P less than 0.05). Fifty per cent of recorded dystocias occurred in ewes stocked at 16 per ha, 40 per cent at 12 per ha and 10 per cent at 8 per ha. Ewe body weight pre-lambing was not related to the incidence of dystocia but it would appear that weaker ewes are more likely to have a difficult birth than ewes that are stronger and in better condition.