Biomarkers of gastrointestinal functionality in dogs: A systematic review and meta-analysis

The identification of key biomarkers that differ between healthy animals and animals with gastrointestinal (GI) diseases may contribute to a deeper understanding of which diet-induced changes may be beneficial for the GI functionality of dogs. Thus, we conducted a systematic review and meta-analysis to assess potential biomarkers of GI functionality in dogs. A systematic search was conducted for randomized controlled and case-controlled trials that evaluated fecal microbiota, α-diversity indexes, the dysbiosis index, and the fecal concentration of short-chain fatty acids, bile acids, and calprotectin in dogs with GI diseases compared to healthy controls or diseased dogs after treatment. A meta-analysis using a random-effects model and inverse-variance was performed to compare dogs with GI disease to healthy controls and dogs with GI disease before and after treatment. A total of 27 studies with 815 healthy dogs and 786 dogs with GI diseases were included in the meta-analysis. Compared to healthy dogs, those with GI diseases presented lower α-diversity (Shannon and Chao1 indexes) and lower abundances of Faecalibacterium, Turicibacter, Blautia, Fusobacterium, and Clostridium hiranonis, as well as greater dysbiosis index and abundance of Escherichia coli (P < 0.05). Dogs with GI diseases also had lower fecal propionate and secondary bile acid concentrations, and greater primary bile acids and calprotectin concentrations (P < 0.05). We can thus conclude that the α-diversity indexes, dysbiosis index, modulation of key fecal bacteria, and the fecal concentration of propionate, bile acids, and calprotectin are promising biomarkers of GI functionality in dogs. As a next step, new studies should evaluate the effects of different dietary interventions on these biomarkers in healthy dogs. Besides, considering that most data were based on dogs fed kibble diets, new studies evaluating these biomarkers in dogs fed human-grade, canned, and raw diets are warranted.