Sélection sur la vitesse de croissance post-sevrage chez le lapin

Abstract

On a effectué une expérience de sélection massale sur la vitesse de croissance entre le sevrage (30 j) et 77 j dans une souche de lapin. La souche sélectionnée se composait de 12 mâles et 60 femelles pendant les 4 premières générations puis de 8 mâles et 40 femelles pendant les 4 suivantes. La souche témoin se composait aussi de 8 mâles et de 40 femelles. On a réalisé une intensité de sélection de 0,95. La vitesse de croissance postsevrage est améliorée de 6,9 g pour 8 générations, soit un progrès de 0,83 g par génération. L'héritabilité réalisée est égale à 0,23. Pour une augmentation d'un g de la vitesse de croissance post-sevrage, on observe une diminution de 0,10 du nombre de lapins vivants à la naissance par portée. Simultanément, le nombre de lapins vivants à 77 j produits par femelle mise à la reproduction a tendance à diminuer. Cette réduction de la fitness est due principalement à une diminution du nombre de femelles ayant fait au moins une portée avec un lapin vivant à 77 j. lapin -sélection -vitesse de croissance post-sevrage -taille de portée -fltness Summary -Selection experiment for post-weaning growth rate in rabbits. A selection experiment was made on the growth rate between weaning (30 days) and 77 days in a rabbit strain. There were 12 bucks and 60 does in the selected strain during the first 4 generations, then 8 bucks and l,0 does during the next 4 generations. There were 8 bucks and 40 does in the control strain. Selection intensity was 0.95. The response in post-weaning growth rate was 6.9 g after 8 generations, i.e. 0.83 g per generation. The realized heritability was 0.23. The increase in post-weaning growth rate was accompanied b an increase in 77-days body weight (58 g) and by a decrease in litter size at birth (-0.10! At the same time, the number of rabbits alive at 77 days per reproductive doe decreased. The main reason for the decrease of fitness was a decrease in the number of does with at least one rabbit alive at 77 days. rabbit -selection -post-weaning growth rate -litter size -fitness

Divergent selection on 63-day body weight in the rabbit: response on growth, carcass and muscle traits

“…Similarly, the estimated heritability value for ADG between 4 and 9 wk was very similar to the value reported by Piles et al [28], but was slightly higher than that reported in rabbits selected on 70-d mass weight (0.17, [18]) or for 4 to 10 wk ADG (0.23, [34]). The high positive genetic correlation between 63-d body weight and 4 to 9 wk ADG, was close to that reported between 70-d body weight and 3-4 to 10 wk ADG (r g = 0.91 to 0.98, [18,40]).…”

“…Successful selection in rabbits was previously shown for ADG [4,22,35] and body weight at market age [18,34]. However, a higher genetic progress for body weights and ADG was obtained in the present work, mainly because of the efficiency of selection on BLUP breeding values in comparison with selection on phenotypic values.…”

“…However, a higher genetic progress for body weights and ADG was obtained in the present work, mainly because of the efficiency of selection on BLUP breeding values in comparison with selection on phenotypic values. For instance, post-weaning ADG was currently increased by nearly 1 g/d per generation of selection on 63-d body weight, versus 0.83 g/d for Rochambeau et al [34] and 0.45 g/d for Piles and Blasco [26] per generation by direct selection on postweaning ADG breeding values. In agreement with previous studies on rabbits selected for ADG [8,22], the lowest feed conversion ratio was observed in the rapid-growing animals, since the genetic correlation between ADG and market weight was high (r g = 0.82 to 0.91, current study, [22]).…”

“…For many years, the aim of genetic selection in rabbit dam lines has been to increase the number of young born alive or still alive at weaning [34]. In sire lines, selection for high growth rate has been largely introduced, but genetic selection on growth rate can modify the whole pattern of growth, the feed efficiency, and the tissue composition, thus affecting carcass and meat quality traits.…”

Selection response of growth rate in rabbits for meat production

“…Then, when the relationship matrix is complete and the animal model is used, the trend in estimated breeding value may give a reasonable approximation to the genetic response for traits of moderate to high heritability. This has been checked by Mrode et al (1989a, b) (Mgheni and Christensen, 1985;Rochambeau et al, 1989) (Camacho, 1989) and there is also evidence that the genetic response in WG is associated with correlated response in SW (Estany et al, 1988b;Camacho, 1989;Rochambeau et al 1989). If that is the case, cross-fostering to equalize litter size would be worthwhile to reduce any maternal effect on SW.…”