Abstract: [Objective] In order to study the effects of Bacillus amyloliquefaciens on milk yield,milk composition,serum biochemical and immune functions of lactating cows. [Method] 36 China Holstein cows with healthy body,milk yield of （35.15±2.10） kg/d,parity of 2.5±0.2 and lactation days of （102±5） d were selected and divided into 3 groups by single factor random design,with 4 replicates in each group and 3 cows in each replicate.The control group was fed with basal diet without Bacillus amyloliquefaciens,and the two experimental groups were designed to be fed with basal diet+150 mg/kg（150 mg/kg group） and basal diet+200 mg/kg（200 mg/kg group） respectively,once a day.The pretrial period is 3 d,and the normal trial period is 56 d.The results showed that the milk protein rate of 150 mg/kg group and 200 mg/kg group increased significantly（P<0.05）.Compared with the control group,the total protein,uric acid and alanine aminotransferase in 150 mg/kg group were significantly increased（P<0.05）,and the urea nitrogen in 200 mg/kg group was significantly decreased（P<0.05）. [Result] Compared with the control group,the contents of IgA and IgM in 150 mg/kg group and 200 mg/kg group all increased correspondingly,among which the IgA and IgM in 150 mg/kg group increased significantly by 50.69%（P<0.05） and 33.64%（P<0.05）,and the γ-interferon in 150 mg/kg group increased significantly（P<0.05）. [Conclusion] In summary,adding Bacillus amyloliquefaciens to the diet can improve the lactation performance of dairy cows and enhance the immune function of the body.

Key words: Bacillus amyloliquefaciens, lactating cow, milk yield, milk component, serum biochemistry, immunologic function