I. Pets are protective factors for the development of IBD in humans Environmental factors have a very important role in the development of inflammatory bowel disease (IBD). In a meta-analysis on environmental health and risk factors for the development of IBD published in Inflamm Bowel Dis 2016, researchers analyzed research results between 1980 and 2015 and found that the ownership of pets or other farm animals among environmental factors was negatively associated with the development of IBD (OR 0.77, 95% CI, 0.63-0.88), a result was not related to the owner’s ethnicity, nor was it related to the age group at which pet ownership began, with the same protective effect of owning a cat or dog. And the same conclusion was reached in an Australian population-based case-control study. The protective mechanism may be mainly related to the pet’s living environment affecting the owner’s immune mechanisms: (1) less exposure to infectious antigenic material favors Th2-mediated immune responses, promoting IL-4, IL-5, IL-6, and IL-13 production, whereas poorer hygiene promotes Th1-mediated immune responses (TNFa, interferonɤ, IL -2); (2) changes in T regulatory cell function; and (3) effects on intestinal microecology, such as higher abundance of Lactobacillus johnsonii in the human intestine in environments with dogs. Second, cats and dogs also have IBD Inflammatory bowel disease in dogs and felines is common in veterinary medicine, and in recent years there have been an increasing number of reported cases and studies on IBD in pets. Diagnosis of IBD requires exclusion of common food-derived diarrhea, diarrhea caused by antibiotics, infectious diarrhea, etc. It also requires differentiation from diseases such as gastrointestinal lymphoma, and confirmation of diagnosis generally relies on histological biopsy (whole intestinal wall biopsy is recommended). The clinical manifestations of the disease vary, and the lack of uniform diagnostic criteria and the difficulty in determining the efficacy of the disease pose a great clinical challenge. The pathogenesis of IBD is thought to be caused by a variety of factors, including abnormalities in the intrinsic immune function of the intestine, infectious factors (parasites, bacteria), dysregulation of fat-soluble vitamins in the body, and disturbances in the intestinal flora. The treatment pyramid of IBD in cats and dogs is: dietary adjustment – antibiotics – immunosuppressants – anti-inflammatory treatment – surgery. Third, the inevitable intestinal microecology changes in the intestinal microecology not only in human IBD, but also in the development of IBD in other animals occupy an important position. Intestinal microecology constitutes a protective barrier for the intestinal mucosa, which helps animals digest food such as fiber and produce substances such as short-chain fatty acids that nourish intestinal epithelial cells. There are differences and commonalities in the intestinal microecology of different species of animals, and certain probiotics that are therapeutic for humans are also effective in the treatment of IBD in pets (e.g., VSL#3). Macrogenomic studies of intestinal flora in cats and dogs have been conducted, and fecal-microbial transplantation (FMT) has been tried and successful in dogs with chronic diarrhea. Changes in intestinal flora in IBD between species (specimens from mucosal biopsies or fecal samples)