Residual feed consumption in laying hens. 1. Quantification of phenotypic variation and repeatabilities.

A large fraction (on average, 25%) of the variance of daily feed consumption among individual laying hens appears unaccounted for by a model with metabolic body weight, daily egg mass production, and body weight gain as independent variables. This unexplained term is referred to as "residual feed consumption" (RFC), defined operationally as the difference between the observed feed consumption of a hen and its consumption as predicted from the model. The study described here deals with the quantification of the phenotypic variation of RFC of hens of a White Leghorn population during a 44-wk laying period (20 to 64 wk of age) in 11 time segments of 4 wk each, fed either a commercial or a low-energy diet (11.7 and 10.0 MJ ME/kg, respectively, where 1 MJ = .239 Mcal). The RFC showed a standard deviation of 4 to 8 g/day. The repeatability of RFC was estimated as .52 to .58. For each time segment between 32 and 56 wk of age, phenotypic correlations between RFC and RFC accumulated over the whole laying period were estimated to be around .8. It was concluded that RFC shows a considerable amount of systematic and permanent variation, and that experimental RFC measurements can be limited to the period between 32 and 56 wk. It was also shown that variation in RFC was caused mainly by differences among hens in maintenance requirements per unit (kilogram.75) of metabolic body weight.(ABSTRACT TRUNCATED AT 250 WORDS)