The Collaborative Collapse: Bile Acid Dysmetabolism as a Central Pathogenic Driver in Canine and Feline Multi-Systemic Disorders—From Mechanisms to Precision Therapeutics

Veterinary metabolomics has redefined bile acids (BAs) from simple digestive surfactants to systemic endocrine signals within a microbial-host metabolic axis. This review aims to evaluate how BA dysmetabolism acts as a central pathogenic factor in canine and feline disease. We analyze the BA pool's integrity, which depends on a specialized functional guild, primarily <i>Peptacetobacter hiranonis</i>, responsible for 7α-dehydroxylation. We delineate two principal pathological profiles: (1) microbial collapse, characterized by secondary bile acid (SBA) depletion and compromised farnesoid X receptor (FXR) and Takeda G protein-coupled receptor 5 (TGR5) signaling, which exacerbates inflammation in chronic enteropathy (CE), protein-losing enteropathy (PLE), and exocrine pancreatic insufficiency (EPI); and (2) hepato-biliary spillover, wherein host-induced dysfunction results in primary bile acid (PBA) excess. Recent data have linked these disruptions to skeletal health, feline renal fibrosis, cardiac remodeling in myxomatous mitral valve disease (MMVD), and neuroinflammation in epilepsy and hepatic encephalopathy. The discovery of microbially conjugated bile acids (MCBAs) and microbial extracellular vesicles (MEVs) reveals highly specific, vesicle-mediated communication pathways impacting systemic health. Diagnostic protocols should prioritize functional profiling, including the dysbiosis index (DI), serum conjugated BA analysis, and SBA/PBA ratios. Clinical management is moving beyond empirical fecal microbiota transplantation (FMT), towards precision synthetic microbial consortia (SynComs), neuroprotective BAs like tauroursodeoxycholic acid (TUDCA), and molecular postbiotics to restore the collaborative metabolome.