The contribution of maternal environment and lamb genotype to growth of lambs from Merino, Poll Dorset × Merino and Border Leicester × Merino ewes

Suffolk-sired lambs from Merino, Border Leicester x Merino and Poll Dorset x Merino dams were either mothered to ewes of their own breed of dam or to ewes of one of the other breeds of dam, with the exception that lambs born from Border Leicester x Merino, and Poll Dorset x Merino dams were not fostered between Border Leicester x Merino and Poll Dorset x Merino breeds of dam. Liveweight and lucerne meal consumption of the lambs and milk yields of the dams were determined during the first 100 days of lactation. Lambs reared by Border Leicester x Merino dams were significantly heavier than those reared by Merino dams at 16 and 23 days of age. They maintained this advantage throughout lactation, though differences were not statistically significant. There were no significant differences in liveweight of lambs between Poll Dorset x Merino and Merino dams. Suffolk x (Border Leicester x Merino) lambs were significantly heavier than Suffolk x Merino lambs at birth and when 9 days of age. They maintained this advantage throughout lactation, though the differences were not significant. Suffolk x (Border Leicester x Merino) lambs were also significantly heavier at birth than Suffolk x (Poll Dorset x Merino) lambs. However, the difference decreased with age so that the liveweights of the two breeds were similar by 80 days of age. There were no significant differences due either to breed of lamb or to breed of dam in lucerne meal intake by lambs and ewe milk yield. We conclude that the lamb's genetic potential for growth and maternal environment were of approximately equal importance in determining the superior growth of lambs born and reared by first-cross Merino dams compared with those born and raised by Merino dams.