Comparison of fi ve animal models and one sire model for weight at birth of creole chickens.

The objectives of this study were to compare five animal models and one sire model and to estimate genetic parameters for body weight at birth from a Creole chicken population in Yucatan, Mexico. Information on body weights was obtained from 758 chickens, progeny of 35 roosters and 140 Creole hens bought from 15 rural communities in Yucatan. Chicks were weighed individually at birth and identified using numbered metallic wing-bands. Roosters and hens were fed with a commercial diet containing 16.5% of crude protein. Data were analyzed by restricted maximum likelihood procedures using five animal models and one sire model. Animal model 1 considered the animal as the only random effect. Models 2 and 3 included, in addition to the additive direct effect of the animal, the common environmental or additive maternal effects, respectively. Model 4 fitted both, the additive maternal and common environmental effects. Model 5 was the same as model 4, except that the covariance between the direct and maternal additive effects was included. The sire model included the rooster and hen within the rooster effects. Animal models 2, 4 and 5 were the best models. Estimates of direct heritability decreased when the maternal additive or common environmental effects were fitted to the model. Estimates of additive direct, maternal and environmental heritabilities from model 5 were: 0.20, 0.18 and 0.35, respectively. The correlation between direct and maternal additive genetic effects was -0.60. This result indicates that the choice of the best animal model should consider the genetic and environmental effects that the reproductive scheme in the population allows, in order to have more precise heritability estimates. [ABSTRACT FROM AUTHOR]