Abstract: [Objective] This study aims to investigate the effect of adding different doses of yeast selenium to the diet on the selenium in yak milk. [Method] Twenty-four mid-lactating yak cows with similar parities and calving times were used as experimental subjects and divided into four groups, each with six cows, with one repetition per cow. The groups included a blank group （grazing only）, a control group （gra 0.5 kg corn meal）, a low-selenium group, and a high-selenium group （grazing 0.5 kg meal, supplemented with 1 mg/kg and 2 mg/kg yeast selenium, respectively）. The experiment lasted for 70 days, with first 10 days as the preliminary period and the following 60 days as the formal period. Yak weights were collected before and after the experiment; 5 mL of milk components were collected before morning feeding and stored at -20℃, and milk production was recorded. [Result] After feeding yeast selenium the high-selenium group showed a significant decrease in weight compared to the blank group, while the control group and the low-selenium group showed a significant increase weight. In terms of yak milk production, an overall downward trend was observed; the low-selenium group had a significantly lower milk production on the first day to the other three groups,while there was no significant difference in milk production at other times. Regarding the selenium content in milk, the selenium content in the of the experimental groups was significantly higher than that of the control group, with the high-selenium group being significantly higher than the other three groups from the 2th to the 40th day. [Conclusion] Adding 2 mg/kg yeast selenium to the diet results in a decrease in a decrease in yak weight but has significant effect on milk production. Additionally， the selenium content in milk is significantly increased. Therefore， adding 2 mg/kg is an optimal solution， but further experiments are needed to determine its optimal addition method.

Key words: yeast selenium, yak, milk yield, milk selenium