Abstract
Data were collected from two consequence generations of light (LBW) and heavy (HBW) body weight lines of Norfa strain. Every completely recorders of 573 and 499 pullets' progeny were used during 1st and 2nd generations, respectively. Four different traits (age at sexual maturity, ASM, body weight at maturity, BWM , egg weight at maturity, EWM , and egg number till 42 wk, EN42wk) were used to construct the general index and four different sub-indices (IS, ASM , IS, BWM , IS, EWM and IS, EN42wk) in each of LBW and HBW lines. The results showed that ASM had low heritability values during the two generations of LBW and HBW lines. On the other hand heritability values of BWM , EWM and EWM ranged from medium to high. The relative economic values of these traits were 6.48 for + 100 g in BWM , 2.25 for + 1 g in EWM , and 1.00 for + 1 egg in EN42wk and zero for zero days of sexual maturity. Generally, it was shown that the main trait of the sub-index had the highest value comparing to the other traits in the same sub-index during 1st and 2nd generations of LBW and HBW lines. The expected genetic change of the main trait of the sub-index was higher than that expected for the same trait in the original index during 2nd generation of LBW and HBW lines. The comparison between the expected and actual genetic gains in LBW during 2nd generation showed that there was a general agreement between the expected and actual genetic gains. On the other hand there were clear discrepancies between the actual and expected genetic changes for ASM, BWM , EWM , and EN42wk in HBW during 2nd generation.