In this context, PCR-DNA sequencing for fragments of SELL (809-bp), ABCG2 (756-bp), SLC11A1 (450-bp), FEZL (813-bp), SOD1 (334-bp), CAT (268-bp), GPX1 (534-bp), and AhpC/TSA (480-bp) genes revealed nucleotide sequence variations in the form of SNPs between mastitis tolerant and affected Holstein and Brown Swiss dairy cows. The gene discussed is CAT; the disease is mastitis.