INTERACTIONS OF SIRE AND FEED COMPOSITION ON THE REPRODUCTIVE PERFORMANCES OF BREEDING DOES

Reproductive performances of 225 cross-bred rabbit does 'Inra 1067', s hed by 15 bucks of the A2066 strain mated to A1077 does were studied o ver I year. These does were fed isoenergetic diets containing 14.9% (B ) or 21.6% (H) crude protein on dry matter basis. The diet did not inf luence litter size at birth or at weaning but individual weaning weigh t and hence litter weight were increased with diet H by 8.2 and 6.5% r espectively. The interaction between sire and feed was investigated at two levels: 1) the structure of genetic variability within each feedi ng and particularly the part of does sire component of variance (which product by 4 is the cross-bred heritability in the strain A2066); and 2) the genetic correlation due to paternal genes between the expressi ons of the same traits in the two feedings, considered as two differen t traits. For litter size (total born alive, weaned) and litter weight at weaning, the sire part of variance was near zero with diet B leadi ng to an heritability of 0.05 on average over these four traits, where as the latter parameter was 0.42 with diet ii. The individual weaning weight on the contrary, gave the same pattern of variability with both diets, with a similar heritability of about 0.14. The estimates of ge netic correlations between the expressions of the same trait in the tw o diets were quite unaccurate, varying between -0.1 and + 1, the true value being likely low, about 0.4, for numerical productivity related traits. According to the proteic level of the feed, the expression of reproductive traits might involve partly different sets of genes.