This study involved 250 lambs reared artificially with milk replacer and solid diet from 2 to 70 days and 316 lambs creep-fed solid diet and reared with their dams from birth to 70 days. Thereafter, all lambs were retained on solid diet to 140 days of age. Heritability estimates for weights of lambs reared artificially tended to be larger than the corresponding estimates for lambs reared with their dams (P > 0.05). Phenotypic variances of lambs reared with their dams were larger at birth and at 35 days, whereas lambs reared artificially had larger phenotypic variances at 70 and 140 days of age. Estimates of genetic correlation between half-sib family means of lambs reared artificially with corresponding half-sibs reared with their dams ranged from 0.15 to 0.91, suggesting the absence of sire × rearing system interaction. We conclude that greater genetic response to selection for lamb weights at various ages could be achieved from direct selection among lambs reared artificially compared to those reared with their dams. However, in the absence of artificial rearing, prospective breeding stock reared with their dams should be tested for postweaning performance to permit full expression of transmitted sire differences. Key words: Sheep, lamb rearing, heritability estimates, genetic correlation