Effect of different levels of selenium yeast on the antioxidant status, nutrient digestibility, selenium balances and nitrogen metabolism of Tibetan sheep in the Qinghai-Tibetan Plateau

Qinghai-Tibetan Plateau is a main area of selenium deficiency in the world, and local grazing livestock are affected by selenium deficiency. We conducted a metabolism trial of Tibetan sheep included adding selenium yeast at 0, 0.2, 0.4 and 0.8 mg Se/kg dry matter (DM) to the native pasture of Maqu county, Qinghai-Tibetan Plateau in 2017, to evaluated the impact of different levels of selenium addition on the selenium balance, nitrogen metabolism, nutrient digestibility and antioxidant status of native forage in Tibetan sheep. Our results showed that selenium balance, absorption and retention of Tibetan sheep were linearly affected by different selenium levels. However, the percentage of selenium retention is the highest when the selenium addition level is 0.4 mg/kg DM. The relationships between selenium addition levels and malondialdehyde (MDA), superoxide dismutase (SOD) and total antioxidant capacity (T-AOC) were quadratic. Based on the prediction equations, the most suitable selenium addition levels for MDA, SOD and T-AOC were 0.39, 0.36 and 0.47 mg/kg DM, respectively. Dietary supplementation of selenium could increase dry matter intake (DMI) and improve food conversion ratio (FCR), and the relationships between selenium addition level and DMI and FCR are both quadratic. Selenium addition could also increase apparent digestibility of NDF, ADF and EE with quadratic effects (P < 0.05). Based on the nutrient digestibility data and the prediction equations, we could get the most suitable selenium addition level is between 0.45 to 0.52 mg/kg DM. Furthermore, selenium supplementation could increase the intake and absorption of nitrogen with quadratic effects and the best predicted levels of selenium addition were 0.52 and 0.54 mg/kg DM, respectively. In summary, selenium supplementation is beneficial to the antioxidant status, digestibility and nitrogen metabolism of Tibetan sheep. Taking into account the predicted levels from different equations and our trial data, the optimum dosage of selenium yeast for Tibetan sheep was 0.4 mg Se/kg DM.