Selection for increased resistance to Salmonella carrier-state.

Improving the fowl's natural ability to clear Salmonella from their body is important in reducing disease prevalence in poultry flocks, as recommended by a recent regulation of the European Commission. It may be efficient, as expected from estimation of heritability coefficients : 0.16 in chicks and 0.18 for global contamination of hens. The animal's age has to be considered since the genetic correlation between resistances at the two ages is negative. Selecting two series of divergent lines for increased or decreased resistance, after inoculation at one week of age (chick resistance) or at the peak of lay (adult resistance) confirmed the efficiency at least of selection for the adult resistance. In parallel, genes controlling variations to Salmonella resistance were researched and several QTLs identified in crosses between experimental lines and, for some of them, confirmed in commercial lines. Thanks to the derivation of a model of Salmonella propagation within a flock, it has been shown that a combination of vaccination and genetic selection can result in very low percentage of contamination.