Survival of lambs affects the profitability of Merino enterprises, with mortality from birth to marking the most prominent factor leading to poor reproductive performance. Survival of lambs following parturition is dependent on the ability to access colostrum and milk, which can be altered by the provision of barley grain to promote lactogenesis and colostrum production when feed availability is suboptimal. The present study evaluated whether the survival of lambs could be improved by supplementing ewes grazing abundant quality pasture with barley grain. Naturally joined Merino ewes (n = 240, 65.5 kg, body condition score (CS) 3) bearing twin fetuses grazing spring pastures (1712 kg DM/ha green, 12.3 MJ ME/kgDM, and 18.5% crude protein at the commencement of the experiment) were allocated to a supplemented or a control diet, with two replicates of each. Ewes were supplemented with 550 g/ewe.day barley grain (12.6 MJ ME/kgDM, 10% crude protein) for 20 days before and 2 weeks following the commencement of lambing (supplemented), or were unsupplemented (control). Ewes gained 0.5 CS and 10.6 kg liveweight from pre-lambing to lamb marking age in both treatments, indicating that their energy intake was high. The proportion of lambs surviving from birth to marking was 0.79 for control and supplemented treatments. Lamb survival was affected by the interaction (P = 0.039) between treatment and sex, with control female lambs having a significantly higher survival than control male lambs. Supplemented lambs reared as singles (17.1 ± 0.95 kg) had significantly (P < 0.05) heavier marking weights than the control lambs reared as singles (14.8 ± 1.1 kg), supplemented lambs reared as twins (14.7 ± 0.71 kg) and control lambs reared as twins (15.5 ± 0.70 kg). Lamb survival was not increased by provision of barley grain in the final weeks before lambing and the first 2 weeks of lambing when ewes were in good CS and grazed ample high-quality pastures.