A Novel Postbiotic Improves Stool Consistency in Dogs: A Randomized, Double-Blind Placebo-Controlled Study

Postbiotics are an emerging ingredient class which have promising potential to support canine gut function by delivering beneficial microbial compounds directly to the gut. We tested a canine immune health postbiotic (CIHP) in a randomized, double-blind, placebo-controlled study of twenty colony-housed dogs (ten per group) selected for having consistently loose stools but with no diagnosed gastrointestinal disease. After a 5-day wash-in and 5-day baseline, dogs received 12 mg/kg body weight per day of CIHP or a placebo for 28 days mixed with their normal dry diet. The primary outcome was stool consistency (Waltham fecal score), measured on Days 0, 14, and 28; secondary outcomes included fecal gut-health biomarkers and fecal microbiome composition from 16S rRNA sequencing, measured on Days 0 and 28. CIHP improved stool quality (p-value = 0.03), while placebo did not (p-value = 0.5), and CIHP showed a trend toward increasing the odds of individual dogs showing improved fecal scores by Day 28 compared to placebo (p-value = 0.07). Microbiome profiling revealed broader community remodeling with CIHP than the placebo (16 taxa significantly shifted with CIHP vs. 1 with the placebo), consistent with stool quality being impacted by both gastrointestinal and gut microbiome functions. Fecal biomarkers that reflect gut health (pH, dry matter, short-chain fatty acids, dysbiosis index, calprotectin) were within reference ranges at baseline and remained stable in both groups, indicating benefits occurred within a normal physiological window. Together, these findings show that CIHP can improve stool consistency while reshaping the gut microbiome in otherwise healthy dogs prone to loose stools. Future studies in home-environment dogs across breeds, ages, and living conditions are needed to generalize these findings to the broader canine population.