Effects of Complementary Feed with Postbiotics Derived from Bacillus subtilis on Nutrient Digestibility, Faecal Characteristics, Gut Microbiota, Metabolic and Immune Responses, and Coat Quality in Healthy Senior Dogs

Abstract

Simple Summary Maintaining a healthy intestinal environment is essential for digestion, immune function, and overall health in dogs. Although probiotics and prebiotics are widely used in pet nutrition, postbiotics have attracted increasing interest because they provide beneficial microbial compounds without containing live microorganisms. In this study, we investigated whether a Bacillus subtilis-derived postbiotic could improve digestive and metabolic health in healthy senior dogs. Dogs receiving the postbiotic showed better digestion of protein and fiber, higher production of beneficial short-chain fatty acids, lower fecal ammonia concentrations, and favorable changes in their intestinal bacterial community. The supplement was also associated with increased blood IgG concentrations, lower cholesterol and triglyceride levels, and improved coat appearance, while no adverse effects on blood or serum trace mineral parameters were observed. These findings suggest that Bacillus subtilis-derived postbiotics may represent a safe and effective functional ingredient for supporting gastrointestinal health, immune function, metabolic status, and coat quality in healthy senior dogs.