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 different ten reduced indices 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, during 1st and 2nd generations of LBW and HBW lines of Norfa strain, there was a negative relationship between the relative efficiency of one or two trait(s) reduced index and the original value of the reduced trait(s) in IG, whereas omitting one or two traits had the highest values in IG caused the less efficient one or two traits reduced index. Furthermore, the trait which had the highest value in original index (IG) also had the highest value in all one trait reduced indices. Concerning to expected and actual genetic gains in the 2nd generation of LBW line there was a good agreement between the expected and actual genetic gain for EN42wk, BWM and EWM by applying most of the reduced indices. On the other hand, there were clear discrepancies between the actual and expected genetic changes for ASM, EWM, and EN42wk in HBW during 2nd generation.