Genetic relationships among milk yield, growth, feed intake and efficiency in laboratory mice.

Abstract

Fifty-seven paternal half-sib families (including 533 lactating female progeny) were formed over three replicates in order to estimate heritabilities and genetic and phenotypic correlations among milk production, feed intake, body weight gain and the efficiency of feed utilization. Milk production was estimated daily from 6 to 21 days of lactation by isolating the litters (size 8) for 6 hr. daily and weighing the entire litter before and after a 1.5-hr. nursing period. A nested model was used to estimate components of variance and covariance to estimate the heritabilities and genetic correlations. The heritability values for gain in weight ranged from 0.12±.10 to 0.22±.12; for feed intake from 0.14±.11 to 0.34±.13; for feed efficiency from 0.11±.10 to 0.24±.12; and for body weight from 0.05±.09 to 0.33±.13. The heritability estimates for milk yield was 0.17±.11, and for 12-day litter weight it was 0.24±.12. The genetic correlations among the preweaning traits, i.e., gain from 5 to 21 days and 12- and 21-day body weight with milk yield were 1.47±.56, 0.74±.80 and 0.92±.35, respectively. Genetic correlations between milk yield and postweaning body weight and early postweaning gain were also large and positive. Calculated relative efficiencies of correlated responses indicated that either 21- or 42-day body weight would serve as suitable genetic indicators of milk yield in mice. Genetic correlations between milk yield and feed intake and feed efficiency measurements were all considerably lower than those for the body weight traits. Postweaning feed efficiency and feed intake were both positively correlated genetically with early postweaning gain. However, feed efficiency and feed intake were negatively correlated. Phenotypic correlations between milk yield and all other traits measured were small. Therefore, it is unlikely that any one of these traits would serve as a suitable phenotypic predictor of lactational milk yield in the mature animal.