Genetic associations between feed efficiency traits and breeding goal traits in Nordic Holsteins

Genetic selection is a viable tool for improving feed efficiency due to its cumulative nature. However, it has not been investigated how selection for feed efficiency affects other breeding goal traits. This work investigated associations between the feed efficiency-related traits BW (representing energy requirement for body maintenance), genetic residual feed intake (gRFI; representing deviations from expected feed intake calculated from milk yield, maintenance, and changes in BW), genetic Feed Saved (gFS; representing deviations from expected feed intake calculated from milk yield, and changes in BW), and all breeding goal traits in the Nordic Total Merit (NTM) index. Phenotypic data were collected from 5,104 cows across 8 commercial herds using the Cattle Feed InTake system, and GEBVs for feed efficiency were estimated using the single-step genomic BLUP methodology. Genetic correlations were approximated using Pearson correlation between GEBVs for different traits. The genetic correlations were weakly negative between BW and NTM (-0.15 to -0.18) or longevity (-0.13 to -0.15), and it was not associated with the yield index. The genetic correlations were generally moderate between BW and conformation traits such as stature and chest width but not with dairy form. The genetic correlations for gRFI in different lactation stages were weakly to moderately correlated with the yield index (-0.23 to 0.21) and weakly correlated with functional traits (-0.10 to 0.10; e.g., mastitis, female fertility). Furthermore, gRFI in early lactation of multiparous cows was weakly and unfavorably correlated with longevity (-0.14). The genetic correlations between gFS and yield, functional traits, and longevity were low (-0.13 to 0.16). However, the moderate negative genetic correlation between gFS and frame (-0.37 to -0.28) indicated that more efficient cows have a smaller frame. In conclusion, our results indicated that feed efficiency traits such as gRFI and gFS can be integrated into breeding goals with limited adverse effects on yield, functional traits, and longevity. Selection for lower BW may enhance longevity without compromising yield.