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Covariance components and genetic parameters of weekly live body weight from hatching to six weeks of age and age of sexual maturation were estimated in a laying type Japanese quail line. The univariate and bivariate animal model analysis included hatching group and sex as fixed effects. Each trait was analysed with animal as random effect to fit the additive direct effect. Additional random effects incorporated in the models were changed according to the trait examined. The best model for a trait was chosen based on a likelihood ratio test, comparing the models with and without maternal additive genetic and maternal permanent environmental effects. Heritability estimates of live-weight at hatch and one to six weeks of age with their standard errors were 0.220.088, 0.390.099, 0.310.086, 0.380.056, 0.460.055, 0.500.059, and 0.560.062, respectively. Direct heritability value of age of sexual maturation was moderate (0.240.055). The variances due to permanent environmental effect of dam after one week of age and maternal genetic effect after two weeks of age were not important sources of variation. The correlations between direct and maternal genetic effects were negative and ranged from high to moderate values (-0.21 to -0.83). Among the weekly live weights, genetic correlations were generally high between not only successive but also early and late weightings. It suggests that selection for final weight may be based on early weight records. Genetic correlations between age of sexual maturation and live weights were low, favourable but had high standard errors. These results indicate that selection for high weight will potentially result in lower age of sexual maturation only with accurate determination of breeding values. |
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