Actavia 0 Matějíček, A. Matějíčková, J. Němcová, E. Jandurová, O.M. Štípková, M. Bouška, J. Frelich, J. 2007 2007-4-30 83-87 The objective of this study was to estimate the joint effects of CSN3 and LGB genotypes on breeding values of milk production parameters. CSN3 (kappa-casein) and LGB (beta-lactoglobulin) genotypes of 120 Czech Fleckvieh sires were detected using the PCR-RFLP method. Breeding values of sires were obtained from the Official Database of Progeny Testing. Ten genotype combinations were detected. Genotypes ABAB (25.0%), ABAA (13.3%) and ABBB (13.3%) were the most frequent. Significant effects of genotype combinations on breeding values for fat and protein content were found. The highest breeding values for milk (+621 kg) and protein (+15.8 kg) yields were associated with genotype combination ABAA, while the highest breeding values for content parameters (+0.15% for protein content and +0.55% for fat content) were associated with genotype combination BBAB. 4 52