This study was carried out within a four years project that aims to develop a synthetic line between the Sinai Gabali breed (G) and the V-line (V). Data of 6278 young rabbits sired by 242 sires and dam reared by 540 dams coming from six different genetic groups of rabbits (represented by G and V purebreds and their crosses; F1, F2, F3 and M line) were used. The recorded traits were: body weight at weaning (BW4), 8 (BW8) and 12 (BW12) weeks of age, as well as daily gain during intervals of 4-8 (DG4-8) and 8-12 (DG8-12) weeks. Using mixed model methodology, estimable functions of genetic type effects were computed and based on them and the matrix of their variance-covariance errors, the crossbreeding parameters were estimated. It was discussed which parameters could be accurately estimated concluding that no matter six genetic groups were involved, only the difference between G and V for the direct additive effects (DG-V), the individual heterosis (HI) and the maternal heterosis (HM) should be considered. The results showed that the differences between G breed and V line were significant for almost all the studied traits, in favor of G breed. Means of F1 rabbits for most traits were significantly higher than the two purebreds. The trend for the average of F2, F3 and M line was to be intermediate between the purebreds and the F1, excepting BW4 and BW8. Positive values of DG-V, the majority of them significant, were obtained on all post-weaning growth traits, confirming the superiority of G over V for growth traits. Percentages of these estimates to the means of the two purebred parents were 5.2, 6.6, 5.3, 11.1 and 21.3% for BW4, BW8, BW12, DG4-8 and DG8-12, respectively, showing an increasing trend as the trait is recorded later. Estimates of HI were always positive and significant for several of the studied traits. Percentages of HI were 6.9, 3.6, 5.4, 9.7 and 6.1% for BW4, BW8, BW12 (significant), DG4-8 (significant) and DG8-12 (significant), respectively. Percentages of HM for the same traits are 7.9, 4.8, -0.0, -8.0 and 2.6%, significant for BW4 and DG4-8. The estimates of the direct additive effects; the values and sign of the average of HI and HM estimated in this experiment; and the complementarity between G (better in growth) and the V line (better in prolificacy) all of them are indicators of the interest of the cross between Gabali and V line and of their synthetic, the Moshtohor line.
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