During the progression of mastitis, the bacterial infection caused the generation of an accentuated reactive oxygen species (ROS) and impairment of antioxidant molecules confirmed in our results by higher malondialdehyde (MDA) levels (p < 0.001), along with a reduction of total antioxidant capacity (TAC) (p < 0.05, p < 0.001) and catalase (p < 0.01, p < 0.001) in mastitic and subclinical mastitic cows compared to the control non-infected one (Figure 3). Here, CAT is linked to bacterial infectious disease.