Effects of dietary antioxidants on glucose and insulin responses to glucose tolerance test in transition dairy cows.

Oxidative stress occurs during the transition period and causes insulin resistance, which may be reduced by the use of antioxidants in this period. Twenty-four multiparous Holstein dairy cows, at 8 wk before parturition, were divided into 4 equal groups, namely control (Ctrl), vitamin E (VE), selenium (Se), and vitamin E plus selenium (VE + Se) groups. On a daily basis, VE and Se cows received dietary 1.5 IU vitamin E/kg BW and 0.3 mg/kg DM selenium, respectively, from 8 wk before to 3 wk after parturition. Vitamin E plus selenium group received doses similar to VE and Se groups. Insulin sensitivity was evaluated through intravenous glucose tolerance test (ivGTT) at weekly intervals from 3 wk before to 3 wk after parturition. Serum concentrations of total antioxidant status (TAS), malondialdehyde (MDA), superoxide dismutase (SOD), glutathione peroxidase (GPx), nonesterified fatty acid (NEFA), and beta-hydroxybutyric acid (BHBA) were assayed weekly before the commencement of ivGTT. Based on the results of ivGTT, the lowest and the highest degrees of insulin sensitivity were detected in Ctrl and VE + Se groups, respectively. The highest and the lowest concentrations of NEFA and BHBA were observed in Ctrl and VE + Se groups, respectively. Total antioxidant status, SOD, and GPx values were significantly lower in Ctrl cows and significantly higher in VE + Se-received cows compared with other groups. However, MDA values in Ctrl and VE + Se cows were significantly higher and lower than the other groups, respectively. Collectively, our results show that dietary administration of vitamin E and selenium ameliorates oxidative stress and lipid mobilization and increases insulin sensitivity in transition cows.