Effect of long-term selection on primary trait (5 week body weight) in synthetic coloured broiler male line- Direct and correlated responses

Abstract

Synthetic coloured broiler male line (PB-1) has been under continuous mass selection for 5week body weight for 15 generations with a target to increase the 6 week body weight of the terminal commercial cross ( Krishibro ) to 1.6Kg. Parent stock is being maintained up to 40 week of age during which some of the important economic traits are being recorded. These traits include body weights at 20 and 40 weeks of age, Age at sexual maturity (ASM), egg weights at 32 and 40 weeks of age and egg production to 40 weeks of age. Direct responses for primary trait( 5 week body weight) were calculated as a regression of generation mean on generation number(Phenotypic response) and regression of control deviated mean on generation number(Genetic response) were obtained. Similarly correlated phenotypic and genetic responses were calculated in secondary traits. Direct response of 5WK bodyweight was -5.01±3.31g on phenotypic scale and 15.54±6.84g on genetic scale. Correlated response for 20WK body weight was -28.32±10.08g on phenotypic scale 1.05±10.43g on genetic scale. For 40WK body weight this was -26.24±11.88g on phenotypic scale and -1.97±9.70g on genetic scale. For 5WK shank length response was -0.48±0.19mm on phenotypic scale and -0.15±0.25 on genetic scale. Phenotypic response in breast angle was -0.70±0.26 degrees and genetic response was 0.07±0.31 degrees. Phenotypic response in 32WK egg weight was -0.066±0.04g and genetic response was 0.005±0.08g.For 40WK egg weight response was -0.035±0.07g on phenotypic scale and 0.03±0.121g on genetic scale. Phenotypic response in ASM was 0.81±0.44days and genetic response was -0.41±0.48days.For 40WK egg production response was -0.43±0.23eggs on phenotypic scale and 0.20±0.18eggs on genetic scale. Phenotypic responses were mostly negative for primary and correlated traits except the ASM. Majority of genetic responses were positive for these traits indicating the improvement of the primary trait over the generations.