Variance components for residual feed intake in dairy cows

Residual feed intake (defined as energy intake minus predicted energy requirements based on lactational performance, metabolic live weight and live weight change) was investigated in 377 lactations on 204 Holstein Friesian dairy cows, fed complete mixed diets ad libitum. Restricted maximum likelihood (REML), and an individual animal model with a random additive, and a random permanent environmental, effect were used to estimate the values of the genetic parameters of several traits. When energy requirement for each cow was estimated from phenotypic regressions then the h² for residual feed intake was estimated to be from 0.30 to 0.38, depending on the way of calculating the energy requirements. Estimates for the genetic correlation between residual feed intake and several other traits showed that this relatively high h² came from high genetic correlations of residual feed intake with live weight change and condition score. When energy requirements were estimated using coefficients based on partial genetic regressions of energy intake on milk energy yield, metabolic live weight and live weight change then the heritability of residual feed intake was only 0.05. The difference between the estimates of heritability for 'genetic' residual feed intake and phenotypic residual feed intake was a consequence of (i) the antagonistic genetic and environmental correlations between live weight change and energy intake and (ii) a strong bias downwards in the estimation of the h² for genetic residual feed intake. It was concluded that there probably is some additive genetic variance for the residual feed intake in Holstein cows. Consequently, measurement of feed intake does provide genetic information additional to that when only production, live weight and live weight change are measured.