ResultsThe Ace and Chao1 indices were higher in Group P than in Group C (P < 0.05), and there was no difference between Groups C and N or between Groups P and N (P > 0.05). There was no significant difference in the Simpson and Shannon indices among Groups C, P and N (P > 0.05). The four main phyla showed no differences (P > 0.05) in composition, while at the genus level, compared with Group C, in Group P, Clostridioides, Blautia and Clostridium_sensu_stricto_1 were increased, while Lactobacillus and Bifidobacterium were decreased (P < 0.05). At the species level, Streptococcus salivarius and Rothia mucilaginosa increased, while Bifidobacterium animals subsp. lactis decreased (P < 0.05). In Group N, at the genus level, Stenotrophomonas, Streptococcus and Prevotella increased (P < 0.05). Compared with those in Group C, the levels of acetic acid, propanoic acid and butyric acid decreased significantly in Groups P and N (P < 0.05), and the areas under the curves (AUCs) of these three SCFAs between groups C and P were 0.73, 0.70, and 0.68, respectively.