The three genotypes of growing rabbits; NMER, Giant Flander, and Egy-line were used to estimate heritability (h²), the common litter effect (c²) and error (e²) in relation to phenotypic variance. In total, 1230 rabbits were produced from four litters in four seasons. Estimates of h² were moderate for all ages studied (5, 8, 14, and 20 weeks). NMER had the highest h² for body weight except at 5 weeks and had a higher h2 for daily weight gain (5-20). NMER had the lowest h2 for feed conversion in the periods 5-8 and 8-14. Estimates of c2 of body weight and daily gain ranged from moderate at 8 and at 8- 14 weeks of age in Egy-Line to high at 20 and at 14- 20 weeks of age in Giant Flander. Egy-Line has been shown to be superior to NMER in body weight at older ages (14 and 20 weeks); it is also greater than Giant Flander and NMER in daily weight gain. Better feed conversion values were observed in Egy-Line. The heaviest weaning weight of rabbits was recorded in autumn for the three genotypes. Body weights increased with the parity order until the third parity. Feed conversion in the second parity was preferred at early ages (5 and 8 weeks), but the best value in the third parity was at older ages. Differences in body weight between Egy-Line and its parents were significantly negative at early ages but significantly positive at older ages. Egy-Line outperformed its parents positively and significantly (P<0.01) in daily weight gain and daily feed consumption. Egy-Line excelled at improving feed conversion. It is concluded that the new synthetic line (Egy-Line) has proven its superiority and good performance genetically over its parents in all the studied traits.