Heritability estimates of performance traits in purebred and crossbred egg type chicken*

The data on performance traits of the pullets of two purebred strains (H & C) and their reciprocal crosses raised in multiple hatches over six generations (1994–2000) of crossbred selection program were analyzed. Heritability of body weights at 20 and 40 weeks of age, age at first egg, egg number to 40 weeks of age, and egg weight during 39–40 weeks of age were estimated using sire component of variance. Pooled estimates of heritability over six generations for body weight at 20 and 40 weeks age was medium for purebreds (0.256±0.078, 0.228±0.071) and high for crossbreds (0.452±0.122, 0.690±0.122). Heritability estimates for age at first egg were 0.232±0.085 and 0.433±0.090 in purebreds and crossbreds, respectively. The corresponding figures for egg number were 0.201±0.092 and 0.259±0.108 and for egg weight were 0.211±0.042 and 0.452±0.119, respectively. The standard errors of heritability estimates were small suggesting that a reasonably high degree of reliance can be placed on these estimates. Large standard errors in crossbreds might be due to smaller population size in comparison to the purebred strains. Heritability of all the traits was higher for the crosses than the purebreds suggesting the buffering qualities of the heterozygous genotypes in relation to the changing environment. Moreover, the additive genetic variation observed among crossbred progenies may contain both the additive genetic variation present in the purebred lines plus the purebred's non-additive genetic variation.