Contribution of social genetic effects in variance components estimation for body weight in Nigerian indigenous chickens raised in a tropical humid location.

Social interactions among chickens can have a great unfavourable effect on economic returns in a poultry farm. The purpose of this study was to use four models to examine the influence of social genetic influences on the variation in body weight of Nigerian indigenous chickens. Sex was treated as the fixed effect within the models. Direct additive genetic, social genetic, and family effects and covariance between direct and social genetic effects were used as random effects. Data were analysed using single-trait animal models which include or exclude social genetic effects. Model comparison revealed that inclusion of full-sib family effect in model 3 did not cause any change in residual and additive genetic variances relative to estimates obtained with model 2. In general, social genetic variance was lower than the estimate for additive genetic variance, but substantially added to the overall heritable variance. For direct hereditary, full-sib family, and residual effects, accounting for heritable social effect in model 4 had a marginal effect on the size of the variances measured. All the estimated residual, additive genetic, social genetic effect, and family variances increased in comparison with model 3. The relationship between direct and social additive effects was positive and not significantly different from 0 (P > 0.05), suggesting autonomy between the direct and social breeding values. In conclusion, the use of models that account for direct effect and social genetic effect of the individual on its group members would entail an optimal individual selection scheme to increase the body weight of chickens.