Gut microbiota Alterations Associated with 1-kestose Supplementation and Owner-reported Aggression-related Behaviors in Dogs

Aims: To characterize fecal gut microbiota features associated with a history of aggression in dogs and to explore whether supplementation with the prebiotic fructooligosaccharide 1-kestose is associated with alterations in gut microbiota composition and owner-reported aggression-related behaviors. Study Design: An exploratory, non-randomized field study comparing aggressive and non-aggressive client-owned dogs, followed by a single-arm pre–post supplementation study in aggressive dogs with owner-reported behavioral outcomes. Place and Duration of Study: The study was conducted in Japan between 2021 and 2023, with a 60-day 1-kestose supplementation period for the intervention group. Methodology: Fecal samples from aggressive toy poodles (Agg; n = 10) and non-aggressive controls (N-Agg; n = 6) were analyzed using 16S rRNA gene sequencing. Dogs in the Agg group received 1-kestose (400 mg/day) for 60 days. Behavioral outcomes were assessed before and after supplementation using the shortened, owner-reported Canine Behavioral Assessment and Research Questionnaire (C-BARQ). Genome analysis of Blautia caecimuris was conducted to identify glycoside hydrolase family 32 (GH32) enzymes, and a recombinant GH32 enzyme was functionally characterized for fructooligosaccharide hydrolysis. Results: At baseline, Agg dogs differed in gut microbial β-diversity from N-Agg dogs and showed higher relative abundances of Mediterraneibacter gnavus, the Segatella copri group, and the Phocaeicola vulgatus group. Following 1-kestose supplementation, M. gnavus was lower, the B. caecimuris group was higher, and the β-diversity difference between groups diminished. In parallel, owner-reported aggression-related C-BARQ items—particularly responses to unfamiliar dogs and strangers near the home—were lower after supplementation. The characterized GH32 enzyme from B. caecimuris hydrolyzed 1-kestose and nystose. Conclusion: These findings indicate that 1-kestose supplementation is associated with concurrent alterations in the canine gut microbiota and owner-reported aggression-related behavioral scores. While causality cannot be established, the results support further investigation of microbiota–behavior associations using larger, well-controlled study designs incorporating objective physiological and microbial measurements.