Abstract: The objective were to determine effects of selenized yeast on lactating Holstein cows performance and in selenium concentrations in the serum and milk. Twenty four lactating Holstein cows with similar parit days in milk, milk yield and body weight were blocked randomized in two groups. All cows were fed a control diet, contained 0.33 mg of selenium/kg of dry matter. Cows in control did not received selenized yeast, and cows in treatment received selenium 0.77 mg/kg of dry matter from yeast. The experimental period was durational for 56 d. There were no significant for animal performance between treatment and control. Selenium concentration of the serum and milk in treatment were 123.1 μg/L and 97.7 μg/L, respectively. In meantime, compared with control, the selenium concentration of serum and milk in treatment was increased by 60.5% and 194.3%, separately. In whole experimental period, the concentration seleium in serum was increase, whereas the concentration seleium in milk was not change after seleium reached a plateau.

Key words: dairy cow; selenized yeast; the selenium concentration of serum; the selenium concentration of milk