Genetic parameters for growth traits in Suffolk and Polypay sheep

Genetic parameters for growth traits in Suffolk and Polypay sheep were estimated using U.S. National Sheep Improvement Program data. Records on 12,814 Suffolks from 65 flocks and 9,028 Polypays from 39 flocks were used. Heritability (h(2)) estimates for weaning weights (WW) at 30, 60, 90, and 120 d in Suffolks were 0.16, 0.14, 0.21, and 0.55, respectively; h(2) for WW at 30, 60, and 90 d in Polypay were 0.07, 0.08, and 0.07. For postweaning gain (PWG), h(2) for models with and without maternal effects were 0.14 and 0.21, respectively, in Suffolk and 0.13 and 0.22, respectively, in Polypay. Maternal effects (additive + permanent environmental) accounted for 16 to 23% of variation in WW through 90 d of age but for 6% or less of the variation in 120-d WW and PWG. Correlations between WW at different ages were uniformly high. Postweaning gain had significant additive genetic correlations with WW at 30 d (1.00) and 60 d (0.69) in Suffolks but was not significantly correlated with 60 d WW in Polypay (0.41). Residual correlations between WW and PWG were small and not significant. Evidence for a modest antagonistic relationship between additive direct and maternal effects on WW was observed in both breeds. (C) 1998 Elsevier Science B.V.