Including fat thickness as a covariate in the regression model used to calculate residual feed intake (RFI) could help preserve carcass quality traits, such as marbling, flavour and juiciness, by accounting for variation in fat deposition. This study aimed to: (1) investigate the benefits of adjusting RFI for rump fat thickness (RFT); (2) estimate variance components and genetic correlations between RFI-calculated with (RFIF) and without (RFIW) adjustment for RFT-and growth, reproduction and carcass traits using genomic information in beef cattle; and (3) compute accuracy, bias and dispersion of RFIF and RFIW genomic breeding values predicted using single-step GBLUP (ssGBLUP). We hypothesised that adjusting for RFT would account for a small proportion of RFI variability, and that genetic parameter estimates would support more balanced selection decisions. Phenotypic records were collected from 9094 Nellore animals (3253 females and 5952 males) over 14 feed efficiency tests conducted from 2011 to 2024. The pedigree included 17,407 animals, of which 5812 were genotyped. Linear and threshold animal models were applied for continuous and categorical traits, respectively. Heritability estimates were low for RFIW (0.17) and RFIF (0.16), with a strong genetic correlation between them (0.98), and a weak genetic correlation between RFIW and RFT (0.15). Spearman correlations between RFIF and RFIW breeding values were high: 0.98 in females and 0.95 in males. Genetic correlations of RFIW and RFIF with growth, reproduction and carcass traits ranged from -0.33 to 0.35. Prediction accuracy was similar for RFIF (0.43) and RFIW (0.44), whereas bias (0.00 for RFIw and 0.00 for RFIF) and dispersion (0.05 for RFIw and 0.03 for RFIF) showed minor differences. Although RFIF captured slightly more genetic variability, the impact was minimal and no differences were observed between RFIF and RFIW. The genetic correlations between RFI and traits related to growth, reproduction and carcass were close to zero to moderate, indicating that selection for RFI is unlikely to negatively impact these other traits. However, it is essential to consider the full set of traits in the selection process to avoid potential drawbacks to the overall genetic progress of the herd.
Temp et al. (Mon,) studied this question.