Genetic Evaluation for Maintenance – Towards Genomic Breeding Values for Saved Feed in Nordic Dairy Cattle
Nordic Cattle Genetic Evaluation NAV (Denmark, Finland, Sweden) is developing an index for Saved Feed, which comprises maintenance and metabolic efficiency. In the launching phase, the index contains maintenance, which is based on breeding values for metabolic body weight (MBW). Therefore, we developed breed-specific genetic evaluations for MBW in Holstein (HOL), Nordic Red Dairy Cattle (RDC) and Jersey (JER). Included data reaches back to the year 1990 and comprise 0.8 million cows with body weight (BW) observations, complemented with first parity conformation observations from 2.9 million cows. BW observations are either based on heart girth measurements (90%) or scale and are used to model MBW in first, second and third parity. Differences in accuracy of measurements and in the number of BW observations per cow are dealt by weighting MBW observations in the statistical models. The applied multiple-trait animal models include six traits: first, second and third parity MBW, and first parity stature, chest width and body depth. Estimated genetic correlations among MBW traits were high (>0.96) and genetic correlations between MBW and conformation traits ranged from 0.65 to 0.68, from 0.53 to 0.58 and from 0.48 to 0.51 for stature, chest width and body depth, respectively. Heritability for combined MBW across the first three parities in HOL and RDC was 0.65 and in JER 0.58. Estimated breeding values for MBW increased on average by 0.8 SDg over the last 25 years in the HOL breed, whereas in the RDC and JER breeds the increase was only 0.4 SDg. We also developed genomic predictions for MBW for which validation reliabilities for genomic breeding values for candidate bulls were 0.59, 0.74 and 0.65 for HOL, RDC and Jersey respectively. The developed index for MBW is negatively correlated with frame, almost uncorrelated with milk production traits, and positively correlated with claw health, calving traits and longevity.
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