Abstract :
Eight hundred one-day-old female chickens from two White Plymouth Rock lines (line L and line ?) and their reciprocal crosses obtained from 40 male and 480 females were used to form four genetic groups (LxL, KxK, LxK and KxL). The aim of this study was to investigate the differences among obtained genotypes, the direct and maternal additive effects and the heterosis with regard to the following traits: body weight from 2 to 10 weeks of age and at 18, 26 and 30 weeks of age, age at sexual maturity, egg production per hen-day until 46 weeks of age, average egg weight (between 32 and 46 weeks of age), liveability during the production period, egg fertility, hatchability of set and fertile eggs. The additive genetic model of Dickerson using crossbreeding program was used to determine the crossbreeding effects. The results demonstrated a statistically significant effect of the genotype on body weight during the different age periods (p < 0.001), age at sexual maturity (p < 0.001), egg production (p < 0.01) and livability (p < 0.05). On the basis of analysis of direct additive effects, it could be concluded that line L was superior for obtaining combinations with more intensive growth rate. Although the lack of direct additive effect with respect to the other traits studied, there was a positive tendency favouring line K. Maternal additive effects had a substantial effect on body weight in most studied periods and livability, favouring line L. The heterosis was important for body weights at different periods of life (3.76-22.33 %), age at sexual maturity (-8.32 %) and egg production (8.25 %) with positive effects on these traits. The results pointed at a mutual complementary effect between both lines as a result of crossbreeding.
