Multi-trait estimation of genetic parameters for body weight in a commercial broiler chicken population

Data from 54 selection rounds (SRs) for growth rate in a commercial broiler chicken line were used for analysis to estimate genetic parameters for body weight (BW) in males and females at three different ages (t-7, t-4 and t days). First BW was recorded at t days of age for 39 SRs, however, as selection continued the birds start to grow faster and attain desired body weight earlier, therefore, the weighing age was changed and BW was recorded at t − 4 and t − 7 days of age for 7 and 8 SRs, respectively. Multivariate animal model was used to estimate genetic parameters for BW in males and females with REML analysis using DMU software package. In males, heritability estimates of BW were found to be 0.37, 0.33 and 0.29 at t − 7, t − 4 and t days of age, respectively, while, in females, heritability estimates of BW at t− 7, t − 4 and t days of age were found to be 0.40, 0.38 and 0.38, respectively. The genetic correlations of BW between males and females at t − 7, t − 4 and t days of age were found to be 0.94, 0.89 and 0.89, respectively, which is significantly different from unity. Also the genetic correlations of BW between ages were significantly different from unity. The heritability and genetic correlation estimates in this study suggest that BW in males and females should be considered as two different traits. Moreover, BW in the three ages should be considered as three different traits.