Breeding for feed efficiency in German Holsteins: the new RZFeedEfficiency

Abstract

A Genomic evaluation has been developed for feed efficiency for German Holsteins and the first official release was in April 2024. As of the release date, more than 327,000 weekly phenotypes of dry matter intake (DMI), body weight (BW) and energy-corrected milk (ECM) were obtained from 14,774 cows from six countries through a collaboration in the resilient dairy genome project. Lactations 1, 2 and 3+ are considered genetically distinct traits. Variance components were estimated with a multi-trait repeatability model, where each of the first three parities was divided into four equal lactation stages. (Co)variance matrices for the random regression model were derived from this multi-trait estimation using the covariance function approach. These are used to obtain genomic estimated breeding values (GEBVs) for DMI, BW and ECM with a single-step random regression model in the routine genetic evaluation. Fixed effects are herd-test-week, inbreeding depression (as a covariate), and calving age by lactation week as a fixed curve (2nd-order Legendre polynomials). The permanent environmental and additive genetic animal effects are fitted as random effects in the model. The averages of heritability estimates for parities 1 to 3, respectively, were 0.19, 0.17, 0.16 for DMI, 0.30, 0.22, 0.20 for ECM and 0.48, 0.45 and 0.50 for BW. The average genetic correlation between parities was 0.79 for DMI, 0.71 for ECM and 0.89 for BW. GEBV for body weight change (BWC) were derived from BW. GEBV correlations of DMI with ECM and BWC were 0.15 and 0.74, respectively. The GEBV correlation between ECM and BWC was -0.07. GEBV for feed saved (FS; expressed in kg DMI), which represents feed efficiency, is then computed from the traits’ GEBV as 0.4×ECM + 4.5×BWC - DMI. GEBV correlations of FS with the milk production index RZM and other main indices in the total merit index are close to zero. The genetic standard deviation of FS is 247 kg per 305 days in milk, which is roughly 3.5% of total DMI per 305 d. Starting in April 2024, the new GEBV for feed efficiency, RZFeedEfficiency, will be published routinely, expressed on a scale with a mean of 100 and a genetic standard deviation of 12.