Heritabilities and Phenotypic, Genetic and Environmental Correlations for Weight, Grade and Condition of Angus Cows1

Abstract

Weights, grades and condition scores taken on 1,371 cows sired by 365 bulls in 13 purebred Angus herds in Virginia were used to obtain estimates of heritability and phenotypic, genetic and environmental correlations among these traits. Models I and II were used to estimate the components of variance and covariance needed for estimating heritability (h2) by the paternal half-sib method, and model III was used to estimate h2 by the dam-offspring regression method. In model I, cow condition score was included as a covariate; in model II, it was not. Heritability estimates for cow weight obtained from models I and II were .38 ± .11 and .29 ± .11, respectively. Corresponding values for grade were .49 ± .13 and .43 ± .13, and the estimate for condition from model II was .31 ± .11. Estimates from the dam-offspring regression analysis were lower, being .22 ± .14 for weight and .10 ± .06 for grade. When cow weight was not adjusted for condition (model II), both among sire and within sire variance components were increased, but the within sire component increased to a greater degree than the among sire component. The genetic and phenotypic correlation estimates among the three traits were positive and moderate in size. Environmental correlations were moderately high and positive from model II but were essentially zero in model I.