The study aimed at determining whether the combination of three selected genes can be used for
selection in small populations of pigs. The estrogen receptor (ESR1), follicle stimulating hormone
(FSHB) and porcine myogenin (MYOG) genes were selected to detect their combined effect. Although over the last decades considerable progress in pig production was achieved, reproduction in this species still remains unsatisfactory. The marker-assisted selection (MAS) is considered to bring progress in pig reproduction. If MAS is to be used efficiently, the complexity of reproduction process should be taken into consideration. The effects were studied of interaction between the mentioned three genes and selected production and reproduction traits of pigs. Interactions between the effects of particular gene markers are important because of possible negative effect(s) of a single-path selection as well as possible co-selection. No significant interaction between the effects of genes studied was found. It is concluded that in small populations co-selection is effective only when highly significant effects of selected auxiliary genes occur.