Abstract: [Objective] To assess the effects of dietary supplementation of active dry yeast （ADY） on feed digestibility and daily gain of fattening Simmental cattle. [Method] A total of 30 Simmental cattle were randomly split into three groups. Group A was the control, groups B and C were the experimental groups. Group A was fed with the basal diet, and groups B and C were fed with the basal diets supplemented with NO.1 ADY （10 g/d） and NO.2 ADY （10 g/d） twice daily, respectively. The pre-feeding phase was 5 days followed by 28 days formal trial period. Fecal separation sieve was used to assess the feed digestibility of the experimental fattening cattle, and the daily gain was monitored. [Result] On day 21 of the experiment, the proportion of up-level fecal sieve residue in group C was significantly （P<0.05） lower than that in group A. On the 28^th day of the experiment, group C had lower proportion of middle-level fecal sieve residue than groups A and B, and was significantly （P<0.05） lower than that on the 7^th, 14^th, and 21^st days of the experiment. The proportion of lower-level fecal sieve residue in group C was the highest on the 28^th day of the experiment, and was significantly （P<0.05） higher than that on the 7^th and 14^th days of the experiment. The average daily gain of the two experimental groups was higher than that of the control group. The average daily gain of group C was significantly （P<0.05） higher than that of group A and group B. [Conclusion] Dietary supplementation of NO.1 and NO.2 ADY increased the daily gain of fattening Simmental cattle and enhanced the feed digestibility to a certain degree. NO.2 ADY exhibited a better effect.

Key words: active dry yeast, fattening Simmental cattle, daily gain, feed digestibility