Combined Vitamin E and selenium supplementation enhances antioxidant status, reduces disease incidence, and improves economic returns in transition dairy cows.

Background and Aim: Dairy cows in the transition period are highly vulnerable to oxidative stress and immune suppression, which increases the risk of metabolic and infectious diseases. Vitamin E (VE) and selenium (Se) are essential antioxidants known to mitigate these challenges, but their combined effects remain underexplored in transition cows. This study aimed to evaluate the effects of VE and Se supplementation-individually and in combination-on oxidative stress biomarkers, immune function, disease incidence, reproductive performance, and economic outcomes in transition dairy cows. Materials and Methods: Forty Holstein cows with similar baseline characteristics were randomly assigned to four groups (n = 10 each): Control (basal diet), VE (3,000 IU/head injected on days 7 and 14 postpartum), Se (1.5 mg/kg body weight orally from calving), and VE + Se (both interventions). Blood samples were collected on calving day and at 7, 14, and 21 days postpartum. Parameters assessed included non-esterified fatty acid (NEFA), β-hydroxybutyrate (BHB), aspartate aminotransferase (AST), blood urea nitrogen, total antioxidant capacity (T-AOC), superoxide dismutase (SOD), glutathione peroxidase (GSH-Px), malondialdehyde (MDA), interleukin (IL)-1β, IL-6, haptoglobin (HP), milk yield, disease incidence, and economic performance. Receiver operating characteristic (ROC) curves assessed VE and Se's predictive value for disease. Results: Combined VE + Se supplementation significantly increased plasma VE and Se levels and improved antioxidant capacity (↑T-AOC, SOD, GSH-Px; ↓MDA) and immune markers (↓IL-1β, IL-6, HP). NEFA and BHB were reduced without affecting AST. The VE + Se group showed significantly lower incidences of mastitis, metritis, and ketosis (p < 0.05). ROC analysis demonstrated high predictive value of plasma VE and Se for disease risk (area under the curve up to 0.973). Economic analysis showed the highest net profit (¥111.91/day) in the VE + Se group. Conclusion: Combined VE and Se supplementation during the transition period enhances antioxidant and immune function, reduces metabolic disease incidence, and improves productivity and profitability in dairy cows. These findings support integrated micronutrient strategies for periparturient health management. Larger-scale and long-term studies are recommended to confirm these outcomes and explore underlying mechanisms.