Selection of young animals in different time periods (based on sequentially increasing data and pedigree files) was investigated in a pig population with a high proportion of imported genetics. The model with genetic groups accounting for different genetic levels of native and imported animals was assumed to be the correct one for selecting the best animals. The objective of this study was to estimate the possible selection loss when the selection decision was based on the commonly used model not accounting for different genetic groups. The prediction of the selection efficiency and selection loss was based on the monetary total breeding value of the selected animals ? young boars after finishing the field test. Different selection intensities were applied (10%, 20% and 50% respectively).