Dietary supplementation of a Lactobacillus postbiotic modulates acute stress responses and impacts temporal variation in the gut microbiome of dogs

OBJECTIVES Stress and anxiety are common in dogs but may be alleviated through dietary interventions targeting the gut–brain axis. This study investigated whether supplementation with a Lactobacillus postbiotic (LB fermentate HF; “LBHF”), previously shown to reduce stress in mice, could attenuate stress responses in dogs. METHODS Twenty-four Beagle dogs, selected for pronounced cortisol reactivity to experimentally induced stress, were randomized to receive LBHF or placebo tablets daily for 28 days while consuming a standard kibble diet. Stress challenges included 3-minute simulated thunderstorm noise test at baseline and day 28, followed by 10-minute road travel stress test the next day. Primary endpoints were plasma cortisol, with heart rate (HR) response as a secondary endpoint. Additional secondary endpoints included changes in fecal microbial communities and metabolomic composition in feces and plasma. After the final challenge, all dogs were transitioned to canned food for one week to induce microbiome shifts. RESULTS Whereas LBHF supplementation only tended to decrease cortisol responses during the thunderstorm noise challenge, it significantly reduced HR reactivity during this challenge, with an average HR reactivity reduction of ~ 20.6 beats per minute compared to placebo (P = 0.021). Microbiome analysis revealed significant LBHF temporal effects, reflected in reduced intragroup variation and greater temporal stability. Concomitantly, pen-level fecal scores improved over time with LBHF. Metabolomic analyses identified an increase in circulating concentrations of tryptophan and other amino acids in plasma of LBHF-treated dogs. Multi-omic integration of fecal metagenomics and metabolomics revealed a strong correlation with HR reactivity. CONCLUSIONS These findings suggest that LBHF supplementation can attenuate physiological stress responses, modulate gut microbiota, and impact concentrations of multiple metabolites in healthy dogs, supporting a role for postbiotics in stress management via the gut–brain axis.