Abstract
Two parallel schemes of crosses were practised involving the Spanish maternal line called V-line (V) and Saudi Gabali (S) rabbits. The first scheme began by crossing Saudi Gabali bucks with V-line does to get the F1 cross (½S½V), then does of this F1 were backcrossed with bucks of V-line to get ¾V¼S, then the progenies of the backcross were inter se mated to get (¾V¼S)2, followed by two more generations of inter se mating of (¾V¼S)2 to get a new synthetic maternal line named Saudi 2. The second scheme began by crossing V-line bucks with Saudi does to get the F1 cross (½V½S), then does of this F1 cross were backcrossed with Saudi bucks to get ½S½V, then progeny of this backcross were inter se mated to get (¾S¼V)2, followed by two generations of inter se mating of (¾S¼V)2 to form a new synthetic paternal line named Saudi 3. A generalised least-square procedure was used to estimate differences between lines in direct and maternal additive effects, direct and maternal heterosis, and direct recombination losses. A total number of 2497 ejaculates of 642 bucks were evaluated for ejaculate volume (VE), pH of semen, sperm concentration (SC), percentage of motile spermatozoa (MS), percentage of spermatozoa with abnormal form (AS), percentage of dead spermatozoa (DS) and libido score (LS). The estimates of direct additive effect for DS (14.2%), SC (12.4%) and AS (12.0%) were moderate and favourable to Saudi rabbits. Maternal additive effects for VE (11.7%) were in favour of genes of V-line carried by the dams of bucks, while these estimates were in favour of Saudi genes for DS (18.6%), AS (13.2%), MS (10.8%) and SC (10.0%). Positive estimates of direct heterosis recorded for SC (13.5%), VE (10.6%) and MS (10.5%) and the negative estimates recorded for AS (−21.5%) and DS (−20.3%) were moderate and well disposed to semen parameters of crossbred bucks. Positive estimates of maternal heterosis for VE (24.0%), MS (21.8%), SC (10.3%) and LS (10.2%) of bucks, and the negative estimates for percentage of DS (−14.7%) and AS (−9.6%) were also significantly favourable. Estimates of direct recombination losses for the majority of semen traits were always not significant.