Mass selection for 70-day body weight in rabbits.

Abstract

Five generations of phenotypic mass selection for increased 70-d body weight (market age, MW) were conducted in an experimental population of rabbits. Market-age weight was recorded for 1,616 rabbits from 336 litters (sired by 121 bucks and reared by 321 does). Additional growth and carcass traits measured in control (C) and select (S) lines were 28-d weaning weight (WW), 28- to 70-d average daily gain (ADG), carcass yield percentage (CY), loin primal cut percentage (LP), and lean-to-bone ratio in the loin primal cut (LBR). Average inbreeding coefficients in litters by the fifth generation were 10.3 and 11.2% for C and S lines, respectively. After five generations the difference in weighted cumulative selection differential between lines for MW was 1,015 g. Using an animal model with REML and regression procedures, observed and realized estimated heritabilities for MW were .12 and .11, respectively. Estimates of heritability by REML were .04, .17, .37, .25, and .35 for WW, ADG, CY, LP, and LBR, respectively. Bivariate REML estimates of direct genetic, common litter, and residual correlations between MW and a second growth trait (WW or ADG) were all positive and moderate to high in magnitude (range of .56 to .98). At generation five, mean direct breeding values of S and C line rabbits for MW were 133.2 and 12.0 g. Genetic trends were 29.1 and 29.4 g per generation for MW, estimated according to regressions of estimated mean breeding value (obtained from mixed-model analyses) or of observed S minus C line mean differences on generation number, respectively. Correlated response for WW, ADG and LBR was consistently favorable, whereas results for other carcass traits studied were inconclusive. Selection was effective for increasing MW performance.

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]). Indeed, a moderate correlated response (r g = 0.50 to 0.64) for weaning weight in rabbits selected on market body weight has been reported previously [18,22]).…”

“…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]). Indeed, a moderate correlated response (r g = 0.50 to 0.64) for weaning weight in rabbits selected on market body weight has been reported previously [18,22]). Interestingly, the common (litter) effect was markedly larger than the direct additive effect for weaning weight, in accordance with Lukefahr et al [18].…”

“…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.…”

“…Indeed, a moderate correlated response (r g = 0.50 to 0.64) for weaning weight in rabbits selected on market body weight has been reported previously [18,22]). Interestingly, the common (litter) effect was markedly larger than the direct additive effect for weaning weight, in accordance with Lukefahr et al [18]. In contrast to this latter study, we obtained similar estimates for the litter effect and direct effect on 63-d body weight and on ADG.…”

“…growth vs. reproductive traits). Selection experiments have been recently conducted on increased average daily gain (ADG) [6,22,35] or phenotypic mass at 70 d of age [18,32], and genetic parameters associated with growth have been estimated. Few within breed studies have also examined the effects of selection for an increased growth rate on carcass fatness, but lower [27] or higher contents [31] in dissectible fat weights have been demonstrated in the selected animals.…”