Inheritance of economic traits in two strains of Rhode Island chickens under selection

Two strains comprising 4336 and 4843 pullets, respectively, of five generat ions (1991-95) under selection for part-period egg production up to 280 day s of age were analysed for heritability estimates, viz., age at sexual matu rity (ASM), egg number to 280 days of age (Egg 280 days), average egg weigh t (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 fo r BWT40 for Strain I. 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 +/- 0.0 3 for BWT40. The heritability estimates for dam component were in most case s, higher than those from sire component for the traits, which showed the e xistence of dominance deviations and (or) maternal effects. The estimates o btained showed considerable variation over generations. The low magnitude o f heritability estimates for production traits indicate that there may be l ow genetic variation in these flocks resulting from continuous selection ov er years, and (or) high environmental influences on the expression of these traits.