Genetic Parameter Estimates of Purebreds and Crossbreds for 35-day Body Weight in Broilers Using Terminal Crossbred Model

Records on 35-day body weight from two purebred broiler lines A (n=15,010), B (n=14,111), and their crosses C (n=7600) were used to estimate genetic parameters using within-line and terminal-cross models. The models that were fitted included the fixed environmental effect (such as contemporary group and sex, day of hatching), random additive and random parental dominance effects. The model for purebreds included only one additive effect, whereas the model for crossbreds included two additive effects (additive effect for sire in A on his C offspring and additive effect for dam in B on her C offspring). Heritability estimates for 35-day body weight were 0.24, 0.226 and 0.24 with within-line models for lines A, B, and C, respectively, and 0.25, 0.23, and 0.25 with the crossbred model, respectively. The ratio estimates of dominance to phenotypic variance were 0.19, 0.32, and 0.11 with within-line models for lines A, B, and C, respectively, and 0.18, 0.33, and 0.11 with the crossbred model, respectively. The genetic correlations between purebreds and crossbreds for 35-day body weight were 0.65 (A-C) and 0.56 (B-C). Mean reliabilities of predicted purebred breeding values were 0.52 and 0.41 with within-line models for lines A and B, respectively, and 0.58 and 0.46 with the terminal-cross model, respectively. Mean reliabilities of predicted crossbred breeding values were 0.64 and 0.42 with within-line models for lines A and B, respectively, and 0.69 and 0.44 with the terminal-cross model, respectively. Mean reliabilities of predicted breeding values using the crossbred model were increased in comparison with within-line model.