Neutrophils are the most pivotal part of the first line of immune defense against invading pathogens in high yielding dairy cows. Their quality and quantity in the body is important. Several pathogens invoke diverse mechanisms to evade the immune defense and facilitate their invasion. The impairment of cellular immunity of dairy cows is one of the fundamental reasons why early lactation-related infections occur. An increased susceptibility of dairy cows to infections has been attributed to a low status of selenium (Se). Selenium, a versatile and essential micronutrient that not only acts as an antioxidant but also participates in redox reactions, is believed to enhance neutrophil functions. This study was, therefore, aimed to determine whether supplemental dietary organic Se (Sel-Plex®) affects on neutrophil function and quality immediately after calving. We fed Holstein cows supplemental Sel-Plex® during the peri-partum period; at 30 d before anticipated calving, the cows were fed diets that provided no Se supplementation (n = 5) or 0.5 mg/kg DM/d (n = 5) of supplemental Sel-Plex®. Treatments continued until approximately 30 d after parturition. The flow cytometry technique was used to measure phagocytosis, respiratory burst, apoptosis and necrosis of neutrophils. Neutrophil phagocytosis did not significantly differ between the two groups. However, organic Se significantly increased the respiratory burst of neutrophils when compared to the control group. Neutrophil apoptosis was decreased remarkably when cows were fed organic Se, but the rate of necrosis only tended to be lower in the treated group. In conclusion, the improved neutrophil functional capacity in peri-partum dairy cows with supplemental dietary Sel-Plex® could lead to a better protection of early lactating dairy cows from infections. These effects could consequently improve the immune and health status of their respective calves as well. Though still remains inconclusive, the application of Sel-Plex® would be further examined in dairy cows for prevention and treatment of especially clinical mastitis.

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