Alterations in Thiol–Disulfide Homeostasis and Oxidative Stress Markers in Cows with Clinical and Subclinical Mastitis

Objective: This study aimed to evaluate alterations in oxidative stress markers and thiol–disulfide homeostasis in cows with clinical and subclinical mastitis. Materials and Methods: A total of 40 cows were included and divided into five groups: clinical mastitis (n = 8), subclinical mastitis (+1, +2, +3; n = 8 for each group), and a healthy control group (n = 8). Blood samples were analyzed for glutathione (GSH), malondialdehyde (MDA), total thiol (TT), native thiol (NT), disulfide levels, and the ratios of disulfide/TT, disulfide/NT, and NT/TT. Results: Compared with the control group, cows with clinical and subclinical mastitis showed significantly lower GSH, TT, and NT levels (P < 0.001), whereas MDA, disulfide concentrations, and disulfide-based ratios were markedly increased, particularly in the clinical mastitis group (P < 0.001). Progressive alterations in oxidative stress markers were observed with increasing severity of subclinical mastitis (P < 0.05). Correlation analyses revealed strong and significant associations between thiol–disulfide homeostasis parameters and oxidative stress markers (P < 0.001). Conclusion: In conclusion, thiol–disulfide homeostasis may serve as a complementary oxidative stress–based biomarker system for the evaluation of both clinical and subclinical mastitis.