Selenium (Se), an essential micronutrient, is believed to enhance neutrophil functions. This study aimed to compare the effects of supplemented organic (Sel-Plex
R ) and inorganic (sodium selenite) Se on neutrophil functions in high-producing dairy cows, during the periparturient period. Twenty-five Holstein cows were randomly allocated to five dietary treatments as follows: control diet (basal diet without Se supplementation), IN 0.3 (basal diet supplemented with inorganic Se at 0.3 mg/kg dry matter (DM)), IN 0.5 (inorganic Se at 0.5 mg/kg DM), OR 0.3 (organic Se at 0.3 mg/kg DM) and OR 0.5 (organic Se at 0.5 mg/kg DM). Some evaluated parameters included neutrophil functions and plasma Se concentrations in cows and plasma Se concentrations in calves. Neutrophil phagocytosis did not significantly differ among the five groups. However, organic Se supplementation significantly increased ( P,0.01) the respiratory burst of neutrophils when compared to cows fed IN 0.3 and the control diet. In comparison to inorganic Se, neutrophil apoptosis was decreased ( P,0.01) when cows were fed organic Se or the control diets. These effects of organic Se on respiratory burst activities and apoptosis of neutrophils were in a dose-dependent manner. Calf plasma Se concentrations were higher ( P,0.05) when cows were fed OR 0.5 and IN 0.5.

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