Among all genes evaluated in the mastitis-affected dairy cows, the highest possible level of mRNA was identified for SELL in Holstein (2.58 ± 0.15) and Brown Swiss (1.85 ± 0.11) dairy cows; whereas, the lowest level was for CAT (0.36 ± 0.03) and ABCG2 (0.52 ± 0.07) in Holstein and Brown Swiss, respectively. The gene discussed is CAT; the disease is mastitis.