Nordic Genetic Evaluation of Feed Efficiency – Updated Model for Saved Feed in Nordic Dairy Cattle Breeds.

Abstract

Since 2019, the Nordic Cattle Genetic Evaluation (NAV) has published breeding values for Saved Feed for Holstein (HOL), Jersey (JER), and Red Dairy Cattle (RDC). This trait is integrated into the Nordic Total Merit (NTM) index. Previously, the genetic evaluation of energy use for maintenance was based on body weight and indicator traits such as stature, body depth, and body width. Metabolic efficiency was genetically evaluated by using a two-step model, where the first step is a pre-correction of phenotypes that introduced challenges. This study developed a one-step genomic model for Saved Feed to both address these challenges and improve the use of research and Cattle Feed InTake (CFIT) data. The dataset comprised 741,491 weekly records from 4,541 JER, 5,377 RDC, and 8,030 HOL cows. SNP genotypes from NAV were used to create breed-specific single-step genomic evaluations. We fitted two-trait random regression models for each of the traits of dry matter intake (DMI), energy-corrected milk (ECM), and body weight (BW) where we treated the first and later lactations as separate traits. The breeding values for BW change (ΔBW) were derived from the BW model. Across lactation (2–44 weeks in milk), the heritabilities ranged from moderate to moderately high for DMI and ECM (0.22–0.50 & 0.47- 0.52) and were moderately high for BW (0.46–0.61). The genetic correlations were strong across parities (≥0.82). These genetic parameters estimated with pedigree based BLUP, were used in three single-step GBLUP models, where lactation-wise breeding values for Saved Feed were calculated within each breed as:

GEBV_{Saved Feed} = 0.40 × GEBV_ECM + 4.0 × GEBV_ΔBW – GEBV_DMI

One index unit of Saved Feed corresponds to 18.3 kg of dry matter saved per 305-day lactation, or 183 kg for 10 index units. Among for candidate bulls born in year 2022, the breeding values for Saved Feed had moderate index correlations with the NTM (0.20–0.30), weak to moderate index correlations with yield trait (0.07–0.26), and low index correlations with female fertility, udder health, and general health (–0.14 to 0.12). For HOL and RDC, the index correlations between Saved Feed and frame size were moderately negative (–0.19 to –0.29), while for JER, this correlation was close to zero. In conclusion, NTM has been updated with the new NAV one-step Saved Feed index which should promote genetic progress for feed efficiency in the Nordic Dairy Cattle breeds.