Phenotypic and genetic trends of performance traits of egg type chickens

Data on production traits over five generation of White Leghorn flock undergoing selection for egg number upto 40 weeks of age were analysed. The genetic and phenotypic parameters of 20 week body weight, age at first egg, egg weight and egg number upto 40 and 50 weeks of age were estimated from sire component of variances and covariances after accounting for the significant fixed effect of hatch in each generation. Phenotypic trend was highly significant (P<0.01) but negative for 20 week body weight while significant (P<0.05) positive trend was observed for egg number upto both ages. Non-significant negative phenotypic trends were observed for age at first egg and egg weight. Genetic trend as regression of heritability on generation number were statistically non-significant for all the traits under study. Estimate of genetic correlation among production traits were of poor precision as they were associated with high standard errors.