Estimation of residual energy intake for lactating cows using an animal model.

Residual energy intake is defined as the remaining energy from total net energy intake after accounting for all energy uses. Residual energy intake is proposed as a measure of feed efficiency because animal efficiency increases as the proportion of accountable energy intake increases or the residual energy intake decreases. Residual energy intake was estimated for each of 247 Holstein cows, daughters of 127 sires and 226 dams distributed in five herds across the US. Data consisted of daily milk production and net energy intake, biweekly measures of milk components, and BW measures taken at varied intervals throughout a lactation. Average daily net energy intake in a lactation was the dependent variable in a model that contained fixed effects of parity and herd-season subclass; covariates of lactation average daily SCM, metabolic BW, and weight change in a lactation; and random animal effect. From this model, residual energy intake was a sum of animal and residual effects. Partial energy requirements for SCM, maintenance, and weight change estimated for all cows were .54, .15, and 1.52 Mcal/kg, respectively. Heritability estimate for residual energy intake was .016; phenotypic standard deviation was 2.455. The proportion of the phenotypic standard deviation in net energy intake that was due to residual energy was 68%.