EN
Genotype and environment interactions, measured by the genetic correlation between the traits of boars offspring performance estimated in test stations, take place at breeding farms or in commercial herds and may be responsible for lower genetic unprovement of commercial herds. The conditions of efficient selection for lean meat growth rate of modern pig types with regard to genotype x environment interaction were discussed. The interaction between genotype and feeding regime during fattening of genetically differentiated crossbreds strongly affects the fattening traits, carcass value and economic results. The phenomenon of different halothane genes expression, depending on slaughter weight, supports the necessity ol intensification of the research work on phenotypic expression of single major genes under different extemal conditions.