Lactation performance, growth, and carcass composition of sheep

Abstract Milk production of Romney, Corriedale, Dorset, Romney × Dorset, and Dorset × Romney ewes was measured in relation to lamb growth in experiments carried out over 3 years (1972–74). Single‐ and twin‐suckled Dorset ewes produced 26–63% and 35–88% more milk (125–132 kg and 133–220 kg respectively) than single‐ and twin‐suckled Romneys during the initial 9 weeks of lactation. Over the same lactation period, milk production in twin‐suckled Corriedale ewes was intermediate (117 kg) between Dorsets and Romneys rearing twins during the 1972 season. Crossbred ewes suckling single lambs showed lev('ls of heterosis for milk production ranging from 6% to 15%. Ewe breed differences in lamb growth performance were less evident than those for milk yields, although by weaning (12 weeks old) twin lambs reared by Dorset ewes were up to 20% heavier (31.6 kg) than twin lambs reared by Romneys (26.3 kg). The correlation between lamb live weight and milk yield over 9 weeks of lactation ranged from 0.53 to 0.70 and 0.17 to 0.51 for single‐ and twin‐suckled lambs respectively. The milk components of protein and solids‐not‐fat were significantly correlated with lamb live weights. Ewe live weights were generally greatest for Dorsets, with the exception of the 1972 experiment; crossbred ewes showed 4% to 7% heterosis.