Crossbreeding effects (additives maternal, additive direct direct heterosis) on performance of economic traits in rabbits in hot climate countries were evaluated. Crossbreeding experiments carried in Egypt reflected desirable additive maternal breed effect in New Zealand White (NZW) rabbits compared to other breeds. For postweaning growth traits, dams of NZW breed may not be the best dam breed. NZW breed is well recognized as a suitable dam breed resource with outstanding maternal abilities based on its high fecundity and milk production. Also, heavy vs medium weight sire breed comparisons revealed significant advantage for growth traits in favour of heavy breeds (Flemish Giant, FG.) The FG used in USA aas Fancy breed may be less efficient. in its overall productivity as purebred than the NZW (as
commercial purebred) due to less favorable maternal abilities (e.g. higher preweaning kit morta.l Ciotnys)e quently, the more appropriate role of the FG seems to be that of a terminal sire breed. In Egypt , superiority of NZW bucks during preweaning period indicates that this breed could be used as an effective terminal .buck breed in a crossbreeding stratification system. In Europe and USA, FG has potential
advantages asa terminal-sire breed for improving postweaning growth carcass performance. The other breeds noted for outstanding dress-lean cutability traits in crossing systems include Champagne D’Argent Californian (CAL) rabbits.
In Egypt, direct genetic effects in NZW-sired litters were more
pronounced at birth and during the 2 1f diarysst of suckling period than at weaning, while Baladi-sired litters recorded the highest direct genetic effect at weaning, the differences between the Baladi and NZW were not significant. The FG-sired rabbits had the heaviest carcass weights but not the best carcass and lean yield values. In Europe and USA,, direct genetic effects on pre- and post-weaning litter and growth traits were .mostlyi n favour of CAL litters vs litters sired by NZW. Moreover, direct genetic effect of FG on these traits were positive high when compared with litters of NZW and CAL paternity. For carcass traits, slight differences in paternity between NZW,C AL and FG were observed.
In Egypt, rabbits mothered by exotic breeds (NZW and CAL in particular) surpassed.in their maternity those rabbits mothered breeds. Breed superiority of NZW maternity compared with FCGA Lf o ra nd preweaning litter traits has been demonstrated in Europe and USA. For postweaning growth and carcass performance, breedmaternity was in of CAL and FG dams. Based on reviewed results, maternal-breed effects appear to be less important than paternal-breed effects in influencing most growth and carcass traits.
its.
In Egypt, crossbreedingbetween different breeds of rabbits Egyptian conditions was associated with the presence of heterotic on litter traits and growth performance. Also, native NZW crossbred rabbits had heavier carcass and leaner cut weights than did native NZW purebreds. Consequently, both producers and processors could potentially benefit economically through commercial production of this
simple cross. In Mexico and Europe, heterosis from including American breeds (e.g. NZW, CA..L etc.) in crossbreeding experiments was equal or superior to those estimates of heterosis from French breeds (e.g. Bouscat). In Brazil, the crossbreeding experiments on NZW, CAL, Chinchilla and Bouscat Giant breeds revealed that crossbreds including
CAL had the highest postweaning growth rate. In Europe, heterosis obtained from crosses including Giant breeds was superior to that of medium-sized breeds (NZW C AaLn)d . Generally, crossbreeding is associated with little improvement in carcass performance. |
