Mixed model methodology for the estimation of genetic response to selection in litter size of rabbits

Abstract Mixed model methodology was applied to estimate genetic trend of three rabbit strains (A, V and B) since there was no control line available. Strains A and V were selected on litter size at weaning by a selection index combining records on the doe, her mother, full sibs and half sibs. Strain B was selected on individual growth rate between 28 and 77 days. All strains were reared under the same conditions. Predictors of genetic values of litter size were obtained by using a repeatability model which included year-season of parity and reproductive state of the female (primiparous; lactating; non primiparous non lactating) as fixed effects. Variance components used to predict genetic value were estimated by using a large amount of data before selection. All relatives were considered when computing the relationship matrix. Genetic trend was estimated by regression of generation average of genetic predictors on generation number. Genetic trends were 0.05 ± 0.01 and 0.03 ± 0.02 weaned rabbits per generation for Strains A (7 generations) and B (6 generations) respectively. Genetic gain in Strain V was 0.16 weaned rabbits after 1 generation of selection.