A five-year crossbreeding project involving Spanish maternal line called V-line (V) and Saudi Gabali (S) rabbits was carried out to produce 14 genetic groups of V, S, ½V½S, ½S½V, ¾V¼S, ¾S¼V, (½V½S)2, (½S½V)2, (¾V¼S)2, (¾S¼V)2, ((¾V¼S)2)2, ((¾S¼V)2)2, Saudi 2 (synthetic maternal line), and Saudi 3 (synthetic paternal line). A total number of 2770 rabbits produced by 91 sires and 402 dams were used to evaluate carcass components, tissue composition and meat quality traits. A generalized least square procedure was used to estimate additive and heterotic effects (direct, maternal, and grand-maternal). The estimates of direct additive effects were significant and in favour of V line rabbits for the majority of traits studied; ranging from 3.8 to 9.0% for slaughter and edible carcass components, 3.4 to 10% for non-edible traits, -3.1 to 9.8 % for tissues compositions, and -14.9 to 2.5 % for meat quality traits. Maternal additive effects were significantly in favour of V line by 1.66% for meat ether extract (11.1% relative to the average of the V line and Gabali as purebreds). Grand-maternal additive effects were not significant in most traits studied except dry matter and ash contents in meat since the effect of the V line was higher than the effect of the Gabali by 0.5% and 1.39%, respectively (0.7% and 15.4% of the respective averages of the pure breeds). Heterosis estimated for non-edible traits were mostly positive and only significant for head weight (direct and grand-maternal heterosis), fur weight (grand-maternal heterosis), lung weight (maternal and grand-maternal heterosis) and viscera weight (maternal and grand-maternal heterosis); the estimates were small relative to the average of purebreds reaching 6.4% as maximum value. Estimates of direct, maternal and grand-maternal heterosis for meat weight were found to be consistent and positive (3.9, 4.5 and 5%, respectively) associated with significant direct heterosis for fat weight (12.2%), maternal heterosis for meat bone ratio (4.5%), and maternal and grand-maternal heterosis for dry matter in meat. The estimates of direct heterois for protein content in meat were significantly positive (1.4%), but the estimates for grand-maternal heterosis were significantly negative (-2.1%). For fat content in meat, the estimates of direct (-8.3%) and maternal heterosis (-11.9%) were significant, while for ash content the estimates for maternal (23.7%) and grand-maternal heterosis (30.1%) were significantly positive.
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