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