Critical Thresholds of Antioxidant and Immune Function Parameters for Se deficiency Prediction in Dairy Cows

The aim of this study was to determine the plasma selenium (Se) levels of lactating cows and to evaluate its association with antioxidant ability and immune function. In a descriptive study, 20 healthy Holstein cows with normal Se level (C) and 30 Holstein cows with subclinical Se deficiency (T) were randomly selected between 14 and 21 days postpartum from a dairy farm, according to a cutoff point of 70 mg/L Se in plasma. Analysis of biochemical parameters of antioxidant and immune function were performed on all the cows, and the risk prediction thresholds for subclinical Se deficiency were determined by area under receiver operating characteristic curve. Cows in the T group had significantly lower plasma Se concentrations compared with cows in the C group (52.16 ± 8.81 vs. 80.37 ± 8.46 μg/L, P = 0.02). There was a marked decrease in plasma glutathione peroxidase (GSH-Px) activity in the T group that correlated positively with the plasma Se level (R = 0.65, P = 0.00), and a significant increase of plasma methane dicarboxylic aldehyde (MDA), total nitric oxide synthase, and lipid peroxidation that correlated negatively with plasma Se levels (R = -0.47, P = 0.01; R = -0.33, P = 0.04; R = -0.40, P = 0.03). Furthermore, there were significantly lower plasma tumor necrosis factor-α and immunoglobulin G levels in the T group that correlated positively with plasma Se levels (R = 0.41, P = 0.01 and R = 0.45, P = 0.01), and a markedly lower plasma interleukin-6 level that correlated negatively with plasma Se levels (R = -0.38, P = 0.02). In addition, if plasma GSH-Px activity was less than 42.37 U/ml, the risk of Se deficiency was significantly increased in lactating cows. These results suggest that low plasma Se levels may reduce the antioxidant ability and immune function, and the risk of low plasma Se level may be predicted effectively by plasma GSH-Px activity in lactating cows.