This project was developed to provide prime lamb producers with information necessary to manage and optimise Merino genetics in their prime lamb production systems. Divergent Merino genetics and nutrition were contrasted and the interaction between environment and genotype was examined. Prime lamb producers can use Merino ram EBVs with confidence to improve liveweight and carcass weight in their terminal cross lambs. Merino EBVs can be used to compare the genetic potential of Merino weaners that have undergone different post weaning growth paths. Merino ewes that grow rapidly from weaning to 300 days of age have increased reproductive potential compared to those that follow traditional “merino-weaner” growth paths and should be used in prime lamb production systems to increase the number of prime lambs produced.