Abstract
Two strains comprising 4336 and 4843 pullets, respectively, of five generations (1991-95) under selection for part-period egg production up to 280 days of age were analysed for heritability estimates, viz., age at sexual maturity (ASM), egg number to 280 days of age (Egg 280 days), average egg weight (EWTAV), body weight at 40 weeks of age (BWT40), rate of lay (Rate), and egg mass. The estimates of heritability pooled over generations from sire, dam, and sire plus dam components of variance, respectively, were 0.15 ± 0.05, 0.2 ± 0.07, and 0.18 ± 0.04 for ASM; 0.13 ± 0.05, 0.16 ± 0.07, and 0.15 ± 0.03 for Egg 280 days; 0.24 ± 0.06, 0.2 ± 0.07, and 0.24 ± 0.04 for EWTAV; and 0.07 ± 0.04, 0.18 ± 0.07, and 0.16 ± 0.03 for BWT40 for Strain 1. The corresponding estimates for Strain 2 were 0.15 ± 0.04, 0.23 ± 0.07, and 0.20 ± 0.03 for ASM; 0.23 ± 0.04, 0.18 ± 0.08, and 0.16 ± 0.03 for Egg 280 days; 0.34 ± 0.05, 0.25 ± 0.06, and 0.29 ± 0.04 for EWTAV; and 0.27 ± 0.04, 0.25 ± 0.07, and 0.21 ± 0.03 for BWT40. The heritability estimates for dam component were in most cases, higher than those from sire component for the traits, which showed the existence of dominance deviations and (or) maternal effects. The estimates obtained showed considerable variation over generations. The low magnitude of heritability estimates for production traits indicate that there may be low genetic variation in these flocks resulting from continuous selection over years, and (or) high environmental influences on the expression of these traits.
