Analysis of reproductive performances during the formation of a synthetic rabbit strain

In 1995, a synthetic rabbit strain ('2666') was formed at INRA for commercial meat purposes by crossing the INRA '2066' strain and the 'V' strain from the Polytechnical University of Valencia (Spain). The development of some reproductive traits and body weight at palpation of the '2666' does was studied from the F1 (first generation cross) to the F4 generation in comparison with the 'V' does. This development was quantified in terms of Dickerson's crossbreeding parameters. The base strains did not differ significantly for any of the studied traits, either overall or in their direct and maternal genetic value. F1 does exhibited significant individual heterosis for body weight (5.5% of the parental average), pregnancy rate (13.3%), total born (18.3%), born alive (24.4%) and weaned (21.0%) per litter born. Concerning body weight, a significant crossbred superiority over the 'V' line was retained in the F2 but not thereafter. The rate of pregnancy showed no crossbred advantage from the F2 on. Concerning litter size traits, the benefit of crossbreeding was maintained until the F4, but at a lower magnitude than in the F1. Body weight and pregnancy rate exhibited maternal heterosis, while litter size did not. Direct epistatic losses were significant for body weight, tended towards significance for pregnancy rate, but did not affect litter size. Overall, the comparison between the synthetic strain and the founders was favourable to the synthetics.