Abstract :
The objective of this study was to investigate genetic merit of return over feed (ROF), which is a herd profit index defined by
CanWest Dairy Herd Improvement as a difference between milk income and feed cost. A multiple-trait (MT) model and random
regression model (RRM) were used. The traits analyzed in MT were rearing cost and ROF of the first three lactations. In RRM, a
cumulative ROF was fitted as function of age and rearing cost was treated as a correlated trait. Variance components were
estimated within a Bayesian framework by Gibbs sampling using a subsample of data. Breeding values were then estimated for
3 041 078 animals using records of 1 951 893 cows. Estimates of heritability for rearing cost from MT and RRM were 0.23 and
0.22, respectively. ROF per lactation and cumulative ROF were negatively correlated with rearing cost. Estimates of heritability
of ROF through the first, second and third lactation from MT were 0.27, 0.10 and 0.08, respectively. Estimates of heritability
of ROF from RRM increased with age and ranged from 0.08 through 0.31. Estimated breeding values (EBVs) for ROF from MT
and RRM were moderately correlated with official EBV for production traits and the Canadian selection index (Lifetime Profit
Index). Herd life EBV had 20.07 and 0.19 correlations with EBVs for ROF from MT and RRM, respectively. From both MT and
RRM, small favorable correlations were reported between EBVs for ROF and for bone quality and angularity, whereas low
unfavorable correlations were reported with EBV for udder depth, front end and chest width. Majority of correlations between
EBVs for ROF and for reproduction traits were near 0, with the exception of EBV for gestation length, calf size and calving
ease, where small favorable correlations were reported. The ROF is a good indicator of cow profitability despite the
fact that it is a simplified profit index that does not account for animal-specific health and reproductive cost. However, because
ROF does not account for differences in heritabilities between components of profit, ROF is not recommended to be used for
direct selection for profit
