Jian Jin, Chao Xu, Wenbin Bao
Fecal microbiota transplantation (FMT) is an emerging microbiome-directed intervention for dogs and cats, but its clinical role remains incompletely defined. This structured narrative review integrates peer-reviewed clinical, mechanistic, methodological, and safety evidence on companion-animal FMT published between 2005 and 2026, with emphasis on efficacy, tolerability, mechanisms, product preparation, donor screening, and research priorities. In dogs, the most consistent clinical signal concerns chronic enteropathy (CE), where observational studies frequently report reduced disease activity scores after FMT, whereas small randomized trials have shown mixed results; however, causal inference remains limited by small sample sizes, heterogeneous diagnostic criteria and treatment protocols, and concurrent therapies. The strongest controlled canine signal comes from parvoviral enteritis, where adjunctive enema-based FMT accelerated diarrhea resolution and shortened hospitalization. Feline data support short-term tolerability and measurable microbiome activity, but clinical efficacy remains preliminary; notably, the first controlled feline chronic enteropathy (CE) trial showed no significant improvement in dysbiosis index or clinical activity scores compared with controls. Proposed mechanisms include donor microbial engraftment, metabolic restoration, immune modulation, and gut-brain and gut-skin axis signaling, although veterinary-specific validation remains limited. Standardized donor screening, batch-level quality control, dose-finding studies, long-term safety surveillance, and adequately powered sham-controlled trials are the main prerequisites for responsible clinical translation.