Genetic analysis of service cock effects on reproductive traits of Betong chickens (KU line) using threshold models
Keywords:Binary trait,, Model comparison, Variance components
The importance of service cock effects was determined on the reproductive traits of Betong chickens (KU line). The traits, namely fertility, early embryonic viability, middle embryonic viability, hatchability of fertile eggs and hatchability of eggs set, were all classified as binary data and were analyzed using a repeatability threshold model. Variance components were estimated using
a Bayesian method with Gibbs sampling. Six repeatability threshold models were fitted and the best model for each trait was chosen based on the deviance information criterion. All models consisted of direct additive genetic and animal permanent environmental effects, and different combinations of service cock genetic, service cock permanent environmental and direct additive-service cock genetic covariance effects. For all traits, the best model was the model with all combinations.
The estimates of direct heritability were in the range 0.032–0.084 with the estimates of service cock heritability in the range 0.039–0.067, estimates of proportion of animal permanent environmental variance to phenotypic variance in the range 0.092–0.244 and estimates of proportion of service
cock permanent environmental variance to phenotypic variance in the range 0.035–0.111. The estimates
of direct additive-service cock genetic correlation were positive in all cases. The low heritabilities indicated that improving environmental conditions would have a large impact on phenotypic reproductive performance in this population of Betong chicken.