Phenotypic and genetic relationships for feed intake, feed efficiency, body composition and cow milk yield measured postweaning and in mature beef cows

Context. Providing feed is the largest cost in beef production. Genetic variation exists in feed efficiency traits in young cattle but the genetic associations with feed efficiency traits in cows are poorly understood, but if strong and favourable, they might be used to improve feed efficiency of cows. Aim. To examine the phenotypic and genetic relationships among feed intake, feed efficiency, body composition and cow milk yield measured in young cattle and in cows. Methods. Data on 1783 young Angus, Hereford, Polled Hereford and Shorthorn bulls and heifers, and for 751 of the females as cows, were used to calculate the phenotypic and genetic relationships among feed efficiency traits, body composition and cow milk yield measured postweaning and in mature cows. The young cattle were tested for feed intake and feed efficiency at approximately 9 months of age and the females, after two calvings, were tested again as non-pregnant, non-lactating cows at approximately 4 years of age. Key results. At the postweaning test, the heritability estimates for feed intake, average daily gain, test weight, residual feed intake (RFI), feed conversion ratio, rump fat depth and eye-muscle area were 0.47, 0.32, 0.46, 0.42, 0.28, 0.47 and 0.20 respectively. Corresponding heritability estimates in the cow test were 0.27, 0.35, 0.74, 0.22, 0.30, 0.47 and 0.12. Heritability estimates for 400-day weight, cow 4-year weight and cow milk yield were 0.47, 0.62 and 0.15 respectively. Genetic correlations between traits measured postweaning and the same traits measured in the cow were moderate to high, and for the feed efficiency trait, RFI, was very high (0.95), close to unity. Conclusions. Inclusion of postweaning RFI as a selection criterion in beef cattle breeding can be expected to lead to improvement in cow feed efficiency. Implications. Most breeding decisions in beef cattle are based on traits measured early in life and for replacement heifers are made with an aim to improve their productivity and profitability as cows. The strong and favourable associations measured between postweaning RFI and cow RFI mean that feed efficiency measured in young cattle can be used as a selection trait to improve cow feed efficiency.