(Co)variance components for milk yield, body condition score (BCS), body weight (BW), BCS change and BW change over different herd-year mean milk yields (HMY) and nutritional environments (concentrate feeding level, grazing severity and silage quality) were estimated using a random regression model. The data analysed included records from 7478 multiparous upgraded Holstein–Friesian dairy cows. There were G×E interactions for BCS across all environments and for BW change across different concentrate levels and silage quality environments. There was a three-fold increase in the genetic standard deviation (S.D.) for BCS change to day 60 of lactation (CS60-5) and a doubling of the genetic S.D. for BCS at day 5 (CS5) as silage quality improved. The genetic variance for CS60-5 increased as concentrate level increased and as grazing severity became tighter. There was significant re-ranking of animals for milk yield, CS5 and CS60-5 over the different HMY environments; genetic correlations fell to -0.60 between extreme HMY environments for CS60-5 and were as low as 0.41 for CS5 across different HMY environments.
- covariance functions
- genetic evaluation