Phenotypic and Genetic Correlations of Feed Efficiency Traits with Growth and Carcass Traits in Nellore Cattle Selected for Postweaning Weight

This study evaluated phenotypic (r(ph)) and genetic correlations (r(g)) between 8 feed efficiency traits and other traits of economic interest including weight at selection (WS), loin-eye area (LEA), backfat thickness (BF), and rump fat thickness (RF) in Nellore cattle. Feed efficiency traits were gain:feed, residual feed intake (RFI), residual feed intake adjusted for backfat thickness (RFI(b)) and for backfat and rump fat thickness (RFI(sf)), residual body weight gain (RG), residual intake and body weight gain (RIG), and residual intake and body weight gain using RFI(b) (RIG(b)) and RFI(sf) (RIG(sf)). The variance components were estimated by the restricted maximum likelihood method using a two-trait animal model. The heritability estimates (h(2)) were 0.14, 0.24, 0.20, 0.22, 0.19, 0.15, 0.11 and 0.11 for gain:feed, RFI, RFI(b), RFI(sf), RG, RIG, RIG(b) and RIG(sf), respectively. All r(ph) values between traits were close to zero, except for the correlation of feed efficiency traits with dry matter intake and average daily gain. High r(g) values were observed for the correlation of dry matter intake, average daily gain and metabolic weight with WS and hip height (>0.61) and low to medium values (0.15 to 0.48) with the carcass traits (LEA, BF, RF). Among the feed efficiency traits, RG showed the highest r(g) with WS and hip height (0.34 and 0.25) and the lowest r(g) with subcutaneous fat thickness (-0.17 to 0.18). The r(g) values of RFI, RFI(b) and RFI(sf) with WS (0.17, 0.23 and 0.22), BF (0.37, 0.33 and 0.33) and RF (0.30, 0.31 and 0.32) were unfavorable. The r(g) values of gain:feed, RIG, RIG(b) and RIG(sf) with WS were low and favorable (0.07 to 0.22), while medium and unfavorable (-0.22 to -0.45) correlations were observed with fat thickness. The inclusion of subcutaneous fat thickness in the models used to calculate RFI did not reduce the r(g) between these traits. Selecting animals for higher feed efficiency will result in little or no genetic change in growth and will decrease subcutaneous fat thickness in the carcass.