EN
Disease resistance of the animals may be improved using both, the conventional (marker assisted selection) and genetic engineering methods. Marker-assisted selection (MAS) can use genetic markers as indices of resistance to diseases. The markers may be devided into exterior traits (e.g. udder and teat conformation – mastitis), determined by serological tests (erythrocyte antigens - leukaemia., MHC antigens - mastitis, leukaemia and tuberculosis in cattle, nematode infection in sheep, Marek's disease in poultry) and molecular analysis of DNA (loci encoding intestinal receptor for K88 and F18 Eschericha coli, MHC genes - mastitis and leukaemia in cattle). Conventional methods should be preferable in improvement of existing resistance mechanisms while the genetic engineering methods (e.g. transgenesis) can be used to introduce into livestock genomes the genes controlling resistance to diseases.