Abstract. The objective of this study was to estimate the effect of acylCoA-diacylglycerol-acyltransferase 1 (DGAT1), leptin and thyroglobulin (TG) loci on the milk fat, milk protein and milk yield in Holstein Friesian, Jersey and Hungarian Simmental cows. Leptin and DGAT1 genotypes were determined by qPCR assay, while TG genotypes were identified using the polymerase chain reaction-restriction fragment length polymorphism technique (PCR-RFLP). DGAT1 GC/GC cows had the highest 305-day milk yield values. Difference between AA/AA and GC/GC genotypes was significant (P<0.05). Leptin CC animals produced significantly higher 305-day milk protein percent values (P<0.05) than other genotypes in Hungarian Simmental breed. At TG locus TT cows showed the highest 305-day milk fat percent values, although differences between genotypes proved to be significant (P<0.05) only in Jersey breed.