Feeding twin-bearing Merino ewes above the metabolisable energy requirements for maintenance during late gestation increases the duration of parturition of the first-born lamb

Context In Australia, approximately 53% of lamb deaths are caused by dystocia. One of the main welfare concerns in the sheep industry is under- and overfeeding ewes, which may be contributing to cases of dystocia. Aims This pilot study aimed to investigate how increasing energy intake affects the duration of parturition and predictors of lamb survival. Methods On Day 100 of gestation (dG), 20 twin-bearing and 10 singleton Merino ewes were selected and allocated to three treatment groups; (1) singleton ewes fed at 1.0× maintenance levels (n = 10); (2) twin-bearing ewes fed at 1.0× maintenance levels (n = 10) or (3) twin-bearing ewes fed at 1.25× maintenance (n = 10). Ewes were housed indoors in individual pens. Urine and blood were sampled from ewes on dG 130, 140, then daily from dG 145 through to parturition, and blood was sampled at the onset of parturition and 30 min post-partum. Urine was analysed for pH and blood was analysed for metabolic parameters, mineral concentration and acid–base balance. Predictors of lamb survival from birth to 24 h consisted of weight, rectal temperature, blood glucose and lactate, and body morphology. Key results Serum calcium in late gestation and blood base excess pre-parturition were higher in Singletons 1M compared with Twins 1M (P < 0.05). The Twins 1.25M group took longer to give birth to the first-born lamb (104.4 ± 21.1 min) compared with the Twins 1M group (44.1 ± 6.6 min; P = 0.015). There were no differences in the predictors of lamb survival measures between the twin-bearing groups (P > 0.05). Conclusions Ewes from the Twins 1.25M group took significantly longer to give birth to the first-born lamb. There were no other significant findings between the twin-bearing groups, including lamb liveweight, however, lambs born to ewes from the Twins 1.25 group were numerically heavier, which may explain the increase in parturition length. Implications Feeding ewes above maintenance did not provide any production benefits to metabolic health or any other physiological parameters. Producers should avoid overfeeding ewes during late gestation.