Abstract
The aim of this study was to improve milk production and fat yield through construction of selection subindices by maximising efficiency of heifer selection. Records of 3225 lactations of 812 cows were used to estimate genetic and phenotypic covariance between body weight at birth of dams and heifers (BW1, BW2) and yields of milk and fat (MY, EY) of dams. Cows were daughters of 185 sires and about 4 cows per sire. All fixed and sire random effects were evaluated in mixed model of Maximum Likelihood procedure. BW1, BW2, MY and EY were the 4 variable for construction 3-type selection subindices. BW1 and BW2 were presented in all subindices. Efficiency of MY and FY subindices varied from 26 to 149% and from 26 to 186%, respectively relatively to the 4-variate subindex. The highest MY and FY genetic gain (76.29 and 27.86 kg/generation) was achieved by MY 3-variate subindex and FY 3-variate subindex. Reduction in MY and FY genetic gains were 30% and 70% with absent of MY from MY 3-variate selection subindices and of EY from FY 3-variate selection subindices, respectively.