BODY-WEIGHT AT BIRTH OF DAMS AND THEIR DAUGHTERS AS A BASE OF HEIFERSSELECTION UNDER HUNGARIAN CONDITIONS .1. MILK AND FAT YIELD IMPROVEMENT

The aim of this study was to improve milk production and fat yield thr ough 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 birt h of dams and heifers (BW1, BW2) and yields of milk and fat (MY, EY) o f dams. Cows were daughters of 185 sires and about 4 cows per sire. Al l fixed and sire random effects were evaluated in mixed model of Maxim um Likelihood procedure. BW1, BW2, MY and EY were the 4 variable for c onstruction 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 sub index. The highest MY and FY genetic gain (76.29 and 27.86 kg/generati on) was achieved by MY 3-variate subindex and FY 3-variate subindex. R eduction 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 se lection subindices, respectively.