Long-term selection responses in economic traits of three purebred layer lines

1. Using phenotypic and pedigree data, genetic parameters were estimated for 12 357 Rhode Island Red-I (RIRI), 13 674 Barred Rock-I (BARI) and 8 481 Colombian Rock (COL) pure line hens. The study focused on age at first egg (AFE), body weight at first egg (BWFE), total egg number by 36 weeks (EN) and average egg weight at 36 weeks (EW).2. The heritability estimates for RIRI, BARI and COL lines were 0.41 ± 0.030, 0.47 ± 0.025 and 0.40 ± 0.025 for AFE, 0.33 ± 0.025, 0.49 ± 0.025 and 0.58 ± 0.030 for BWFE, 0.44 ± 0.025, 0.33 ± 0.025 and 0.44 ± 0.025 for EN and 0.41 ± 0.021, 0.40 ± 0.025 and 0.32 ± 0.025 for EW, respectively.3. The genetic correlations ranged from -0.81 ± 0.013 to 0.86 ± 0.034, while phenotypic correlations ranged from -0.64 ± 0.025 to 0.80 ± 0.013 for the emphasised traits. The strongest genetic and phenotypic correlations were observed between AFE and BWFE in the COL line.4. The selection programme aimed to reduce AFE, optimise BWFE and improve EN and EW, with varying degrees of response observed across breeds. Genetic trends showed significant decreases in AFE and BWFE and positive gains in EN and EW across all breeds. Phenotypic trends were generally consistent with genetic trends for AFE and BWFE, while greater divergence was observed for EN and EW, especially in the COL breed.5. The results suggested that successful layer breeding requires balancing genetic selection with environmental management and implementing breed-specific strategies.