Influence of the rabbit's sire genetic origin and the season of birth on the litter performance in the organic production system. Preliminary results

In Italy, the organic rabbit production (ORP) must follow the guidelines for organic livestock system (EC regulation 1804/1999). The present study compared the performance of litters derived from two sire genetic origins (SGO), Vienna Blue (B) and Burgundy Fawn (F), along the 4 seasons of birth (SB), in the ORP system. Sixty-one litters from B and 60 from F SGO were used. The pups were born from January to November. Born per delivery (n), born alive per delivery (n), individual weight of born alive (g), weaning age (d), litter size at weaning (n), individual weight at weaning (g), litter weight at weaning (g), pre-weaning mortality (%) and preweaning growth (g/d) were studied. ANOVA tested the SGO, the SB and their interaction as fixed effects. The performance of the litters derived from the two considered SGO’s was very good for litter size at birth (8.4) and at weaning (7.4), for the weight of born alive (63.3 g) and, especially, for the pre-weaning mortality (15.4%). The SGO didn’t influence the litter performance. The SB effect was much more considerable, and determined a greater number of born per delivery in winter than in the other 3 seasons (9.5 vs. 8.6, 7.8 and 7.5; P<0.05), lighter newborn pups in winter and heavier in autumn (58.1 vs. 69.1 g; P<0.05), higher individual weaning weight in summer than in spring (1137 vs. 970 g; P<0.01), but the weaning litter weight was found to be higher in winter, if compared to spring and summer seasons (8522 vs. 7215 and 7011 g; P<0.05), because of the significantly higher weaning litter size of pups born in winter than in summer (8.4 vs. 6.5; P<0.01). The best growth performance was observed in summer and the worse in spring (23.4 vs. 17.7 g/d; P<0.001), with intermediate performance in winter and autumn (20.6 and 19.5 g/d). The pre-weaning mortality was unaffected by the SB. The increased environmental temperature during the pre-weaning life of litters born in spring significantly compromised their growth. In conclusion, the pups of the 2 SGO showed good pre-weaning performance and seemed to be suitable to the ORP system.