In order to study the effects of different proportions of wheat particle added to the diet on the fermentation parameters, digestive enzymes activities, immune function, antioxidant capacity and microbial structure and composition, 90-d-old male Tibetan lambs with similar weight [(21.87±2.35) kg], consistent parity and good development were randomly divided into three groups. In these groups, 0 (CPW), 10% (LPW) and 15% (HPW) wheat were used to replace maize in the diet. At the end of the experiment, trial lambs in each group were slaughtered randomly, the rumen fluid were collected, and the fermentation parameters, digestive enzymes activities, immune function, antioxidant capacities and bacteria were determined. It was shown that the contents of acetic acid and butyric acid in the CPW group were significantly (P<0.05) higher than those in the HPW group. The activities of α-amylase, cellulase, chymotrypsin and trypsin in the CPW group were significantly lower than those in the LPW group. The immunoglobulin A and immunoglobulin G in the LPW group were significantly higher than those in the CPW group, but the tumor necrosis factor-α (TNF-α) content was the opposite. The total antioxidant capacity of the HPW group was significantly higher than that of the CPW group, while the catalase activity of the HPW group was significantly lower than that of the LPW group. There was no significant difference in the rumen bacterial diversity among three groups. At the phylum level, Firmicutes, Bacteroidetes and Actinobacteria were the dominant phyla. At the genus level, F082_unclassified, Ruminococcaceae_NK4A214_ group, Succiniclasticum, Shuttleworthia, Prevotella_1 were dominant. Function prediction showed that rumen bacteria were mainly enriched in amino acid metabolism, metabolism of cofactors and vitamins, and translation, etc. In conclusion, addition of the appropriate level of wheat instead of maize in the diet had no significant effect on rumen fermentation function and bacterial community structure of Tibetan lamp, and could enhance digestive enzymes activities, antioxidant capacities and improve body immunity. The recommended ratio of wheat instead of maize was 10% in the experiment conditions.
