Gut Microbiota and Selected Systemic Biomarker Profiling in Dogs with Distinct Osteoarthritis Phenotypes.

Canine OA phenotypes show subtle gut microbiota differences, with TNF-α higher in thin versus obese OA dogs.

This observational study investigated gut microbiota composition and systemic inflammatory biomarkers in client-owned dogs stratified into three groups: clinically healthy controls (CG), obese dogs with osteoarthritis (OOA), and thin dogs with osteoarthritis (TOA). Fecal microbiota profiling was conducted using near full-length 16S rRNA Nanopore sequencing, while circulating lipopolysaccharide (LPS), lipopolysaccharide-binding protein (LBP), and TNF-α were measured as systemic biomarkers. Alpha diversity was reduced and Firmicutes/Bacteroidota ratios were lower in OOA dogs compared to controls. PERMANOVA revealed statistically significant phylum-level compositional differences among phenotypes (R² = 0.121, p = 0.002), which persisted after adjustment for age, sex, and body weight (R² = 0.095, p = 0.009). However, lower taxonomic-level associations became non-significant following multivariable adjustment and false discovery rate correction. LPS and LBP concentrations did not differ significantly among groups. TNF-α differed significantly between OOA and TOA dogs after covariate adjustment (p = 0.014), with TOA dogs showing higher back-transformed estimated marginal means (38.5 pg/mL) compared to OOA dogs (27.5 pg/mL). Associations between microbial variables and circulating biomarkers were weak and did not survive false discovery rate correction. The authors conclude that naturally occurring canine OA is associated with subtle, phenotype-dependent microbial ecological changes rather than overt global dysbiosis, highlighting OA as a metabolically and microbially heterogeneous condition influenced by obesity status.

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