Abstract: This study was aimed to evaluate the effects of the immune regulator “polyactin A” on immune function, intestinal barrier and intestinal flora in dogs modeled for ulcerative colitis (UC). Twenty-four 10- to 11-month-old Beagle dogs were randomly divided into four groups, each group contained six dogs. The Control group and the Model group were fed the basal diet, and the Low-dose group and the High-dose group were added 1 000 and 2 000 mg·kg^-1 of polyactin A to the basal diet, respectively. The Model, Low-dose and High-dose groups were established by rectal instillation of 7% glacial acetic acid at 2 mL·kg^-1 for UC model on day 0 of the experiment, The Control group was rectal instilled with the same dose of saline and continued for be fed 7 weeks. The results showed that: 1) The dogs in the Model group, Low-dose group and High-dose group showed posterior urgency, turning back to look at the abdomen, restlessness, unformed and bloody stools, and endoscopic findings showed congested and edematous intestinal mucosa with obvious ulcers 24 h after modeling. 2) Compared with the Control group, serum IL-6 was significantly higher (P<0.05) and IL-10 was highly significantly lower (P<0.01) in the Model group, while serum IL-6 and IL-10 returned to normal levels in both the Low-dose and High-dose groups. In addition, the fecal SIgA levels were also significantly higher in the Low-dose and High-dose groups compared with the Model group (P<0.05). 3) On day 49 of the test, serum LPS levels were significantly higher in the model group compared with the Control group (P<0.05); serum LPS levels in the Low-dose group and serum DAO levels in the High-dose group were significantly lower compared with the Model group (P<0.05). 4) Compared with the Control group, the intestinal flora structure of the Model, Low-dose and High-dose groups all differed significantly (P<0.05), and the relative abundance of Lachnospiraceae in the Model group increased significantly; compared with the Model group, the difference in the flora structure of the Low-dose group was not significant (P>0.05), and the difference in the flora structure of the High-dose group was highly significant (P<0.01), with Ruminiclostridium was significantly increased in the Low-dose group (P<0.05) and Megasphaera was significantly increased in the High-dose group (P<0.05). In conclusion, the addition of polyactin A to dog food can improve the immune function, the physical barrier function and the flora structure of the intestinal tract in UC-modeled dogs, and the addition of 0.2% polyactin A to dog food is recommended.

Key words: polyactin A, caine ulcerative colitis, immune function, intestinal barrier, intestinal flora