Genetic and phenotypic variance and covariance components for feed intake,feed efficiency, and other postweaning traits in Angus cattle

Records on 1,180 young Angus bulls and heifers involved in performance test s were used to estimate genetic and phenotypic parameters for feed intake, feed efficiency, and other postweaning traits. The mean age was 268 d at th e start of the performance test, which comprised 21-d adjustment and 70-d t est periods. Traits studied included 200-d weight, 400-d weight, scrotal ci rcumference, ultrasonic measurements of rib and rump fat depths and longiss imus muscle area, ADG, metabolic weight, daily feed intake, feed conversion ratio, and residual feed intake. For all traits except the last five, addi tional data from the Angus Society of Australia pedigree and performance da tabase were included, which increased the number of animals to 27,229. Gene tic (co)variances were estimated by REML using animal models. Direct herita bility estimates for 200-d weight, 400-d weight, rib fat depth, ADG, feed c onversion, and residual feed intake were 0.17 +/- 0.03, 0.27 +/- 0.03, 0.35 +/- 0.04, 0.28 +/- 0.04, 0.29 +/- 0.04, and 0.39 +/- 0.03, respectively. F eed conversion ratio was genetically (r(g) = 0.66) and phenotypically (r(p) = 0.53) correlated with residual feed intake. Feed conversion ratio was co rrelated (r(g) = -0.62, r(p) = -0.74) with ADG, whereas residual feed intak e was not (r(g) = -0.04, r(p) = -0.06). Genetically, both residual feed int ake and feed conversion ratio were negatively correlated with direct effect s of 200-d weight (r(g) = -0.45 and -0.21) and 400-d weight (r(g) = -0.26 a nd -0.09). The correlations between the remaining traits and the feed effic iency traits were near zero, except between feed intake and feed conversion ratio (r(g) = 0.31, r(p) = 0.23), feed intake and residual feed intake (r( g) = 0.69, r(p) = 0.72), and rib fat depth and residual feed intake (r(g) = 0.17, rp = 0.14). These results indicate that genetic improvement in feed efficiency can be achieved through selection and, in general, correlated re sponses in growth and the other postweaning traits will be minimal.