Genomic evaluation for feed efficiency in Canadian Holsteins

Genomic evaluation was developed for feed efficiency for Canadian Holsteins, with the first official release in April 2021. The model defines all traits in two periods of first lactation: 5-60  and 61-305 days in milk. Traits are: a) Metabolic Body Weight (MBW), calculated as (body weight) 0.75 ; b) Energy Corrected Milk (ECM), calculated as 0.25*Milk + 12.2*Fat + 7.7*Protein; and c) Dry Matter Intake (DMI). All traits are weekly averages expressed in kg/day (ECM and DMI) or kg 0.75 (MBW). Single-step method is used to fit the multiple-trait linear animal model for 6 traits (ECM, MBW, and DMI, in two DIM intervals) with genotypic information, using the MiX99 software. GEBV of DMI are re-parameterized using linear regressions of DMI on ECM and MBW, giving a measure of feed efficiency (RFI) genetically independent of ECM and MBW.  Genetic parameters were estimated using 99,713 weekly records on 4,952 cows. Heritability of RFI was 0.10 and 0.05 for early and later periods in first lactation, respectively, and were smaller than estimates for DMI (0.29 and 0.27). By definition, RFI and the energy sink traits were genetically uncorrelated. Correlations between DMI and RFI were 0.50 and 0.37 for first and second DIM intervals, respectively. Finally, RFI in 5-60 DIM was genetically less correlated with RFI in 61-305 DIM compared to DMI between these two DIM intervals (0.63 vs. 0.88). Estimated breeding values (GEBV) for RFI are reversed in sign and proofs are expressed as RBV (mean = 100 and SD = 5, for base bulls). Proofs for RFI in 61 – 305 DIM, labeled as Feed Efficiency (FE), are considered a principal selection criterion for feed efficiency in Canadian Holsteins. Average reliability of FE for young genomic bulls was 0.41.