Abstract: The aim of this study was to investigate the effects of different ammonia concentration on production performance, immunity and antioxidant capacity of beef cattle. In this study, 16 healthy Qinchuan cows with an initial weight of (220±5) kg were randomly divided into 4 groups with 4 replicates per group and 1 cattle per replicate.Treated with ammonia at concentrations of<5 (control), (15±3), (30±3) and (45±3) mg·m^-3, respectively. The advanced experiment period was 10 days and the formal period was 30 days. During the trial period, the production performance was recorded(ADG,ADFI and F/G), and serum samples were collected from the jugular vein at day 1, 15, 30. Then the biochemical indicators, immune globulin,cytokines and antioxidant enzymes activities were measured.The results showed as follows:1) Compared with the control group, average daily gain (ADG) significantly decreased when ammonia concentration was 30 mg·m^-3, and average daily feed intake (ADFI) was significantly decreased in all ammonia treatment groups (P<0.05), and feed∶gain (F/G) increased significantly when ammonia concentration was 15 and 30 mg· m^-3 (P<0.05). 2) The content of serum CRE、BUN、ALT、AST and LDH were significantly increased when the ammonia concentration was 45 mg·m^-3 (P<0.05), and the An content increased significantly in all ammonia treatment groups compared with the control group, indicating that ammonia exposure caused damage to liver and kidney function of cattle. 3) The immunoglobulin A (IgA) level was significantly reduced in each ammonia treatment group (P<0.05), the content of IgM was significantly decreased when the ammonia concentration was 30 and 45 mg· m^-3 (P<0.05). However, there was no significant difference in IgG content among the groups (P>0.05). Ammonia exposure significantly increased the levels of IL-6 at 30 and 45 mg·m^-3， and IL-4 content was significantly increased at 45 mg· m^-3 (P<0.05), IFN-γ content was significantly reduced at 30 and 45 mg· m^-3 (P<0.05), thus inducing an inflammatory response of beef cattle. 4) Ammonia exposure significantly decreased T-AOC activity at 30 and 45 mg· m^-3 and GSH-Px activity was significantly decreased at 45 mg· m^-3 (P<0.05)， MDA content significantly increased at 30 mg· m^-3 (P<0.05);No significant difference was observed in the serum SOD and CAT activities in each group (P>0.05). In summary, this study suggested that excessive ammonia exposure reduced growth performance, impaired immunity and antioxidant capacity of beef cattle.

Key words: beef cattle, ammonia, growth performance, immune, antioxidant capacity