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

Abstract. Data on 17,588 pulletes of two strains selected for egg number and egg weight along with a control line were examined over seven generations. Significant desirable realized genetic gains/generation were observed for egg number 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 desirable responses were also observed for egg mass (175 and 151g), rate of lay (1.0 and 1.37%), egg production efficiency (0.08 and 0.07) and efficiency 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 any significance in affecting the performance and heritabilities. The additive genetic and phenotypic variances and heritabilities remained stable over generations. Realized heritabilities varied between 0 18 and 0.29 for egg number and between 0.44 and 0.66 for egg weight and indicated the effectiveness of the criterion of selection.