Heritabilities and Genetic Correlations from a Selection Experiment in Broiler Breeders using Restricted Maximum Likelihood.

Derivative-Free Restricted Maximum Likelihood (DFREML) procedure was used with a reduced animal model to estimate variance components for body weights at 7 and 30 weeks of age, age at first egg and egg weight at 34 weeks of age in broiler chicken. The mixed linear model took account of year, sex and house as fixed effects. The same type of analyses were carried out on sums of measurements of different combinations of the four traits for the purpose of obtaining covariance components between pairs of traits. Data were from a selection program on 5 1ines of White Plymouth Rock chicken and 4 1ines of White Cornish chicken at the National Livestock Improvement Center, Hyogo Station. Heritability estimates for body weights at 7 weeks and 30 weeks of age were between 0.10 and 0.34 for all lines. Heritability estimates for egg weight were between 0.46 and 0.68 while those for age at first egg ranged from 0.18 to 0.63. Heritability estimates for body weight traits were low compared to other values cited in the literature, while those for age at first egg and egg weight were comparable to other literature estimates. Estimates of genetic correlations between body weight at 7 weeks of age and body weight at 30 weeks of age, egg weight, and age at first egg were 0.21 to 0.71, -0.10 to 0.38, and-0.15 to 0.75, respectively. Body weight at 30 weeks had genetic correlation estimates of 0.14 to O.34 and-0.19 to 0.89 with egg weight and age at first egg, respectively, while the genetic correlation between egg weight and age at first egg was estimated at-0.21 to 0.26.The low to moderate heritabilities obtained for the weight traits indicate that the use of predicted breeding values obtained by animal model-BLUP for selection will be more effective for the achievement of rapid genetic gains.