Selection for Egg Mass in Different Social Environments 2. Estimation of Parameters in Selected Populations ,

Data on hen-housed egg mass, the criterion of selection, and associated egg production traits were obtained from pullets of four strains selected over four generations in intermingled- or separated-family flocks. Data from the foundation stock also were used. Least squares estimates of phenotypic means, components of variance and covariance, heritabilities, and correlations (genetic, environmental, and phenotypic) were computed. Parameter estimates were regressed on generation number. No apparent time trends were found. Evidence was inconclusive for random genetic drift between strains within selection systems. Egg mass is estimated to be a lowly heritable trait (weighted means from sire component analyses ranged from 0.05 ± .03 to 0.16 ± .04). Egg weight is moderately heritable (sire component estimates of 0.32 ± .06 to 0.45 ± .04). Low heritability estimates (mean ranges of .05 to .13) were found for age at sexual maturity, hen-day, and hen-housed rates of lay. Genetic correlation estimates were high and positive between egg mass and rates of lay (sire component estimates ranged from .82 to 1.0). Egg mass and egg weight were moderately correlated genetically (.31 to .73). Genetic correlation estimates were low between age at sexual maturity and egg weight with mean ranges for estimates of −.06 to .12. Moderately large and negative genetic correlation estimates were obtained between age at sexual maturity and rates of lay.