Direct and correlated responses to selection in two flocks of White Leghorn

Data on 17,588 pulletes of two strains selected for egg number and egg weig ht along with a control line were examined over seven generations. Signific ant desirable realized genetic gains/generation were observed for egg numbe r to 40 weeks (2.18 and 2.23 eggs) and egg weight (0.81 and 0.45g) in both the strains. Significant correlated responses were also observed in age at first egg (-1 .54 and -1.17 d); 20 and 40 week body weights (8.8 to 19.0). Significant de sirable responses were also observed for egg mass (175 and 151g), rate of l ay (1.0 and 1.37%), egg production efficiency (0.08 and 0.07) and efficienc y index (1.09 and 1.03 g/d/kg). Natural selection did not seem to play any role. Inbreeding of 0.28 to 0.45% per generation did not appear to be of an y significance in affecting the performance and heritabilities. The additiv e genetic and phenotypic variances and heritabilities remained stable over generations. Realized heritabilities varied between 0.18 and 0.29 for egg n umber and between 0.44 and 0.66 for egg weight and indicated the effectiven ess of the criterion of selection.