The pet food industry has increasingly shifted from basic nutritional support toward functional strategies targeting gut health, immune modulation, and recovery from microbiota disruption. Kefir is a fermented food containing a complex consortium of lactic acid bacteria, yeasts, and acetic acid bacteria, which has been widely studied in humans but remains insufficiently characterized as a functional ingredient for companion animal nutrition. This review aims to systematically summarize recent in vivo and in vitro studies investigating the effects of kefir and kefir-derived microorganisms on gut microbiota composition, fermentation activity, and short-chain fatty acid (SCFA) production in dogs, and to discuss its potential application in functional pet food development. Peer-reviewed studies focusing on kefir-related interventions in dogs, including short-term feeding trials and in vitro fecal fermentation models, were reviewed. Evidence regarding microbiota modulation, fermentation kinetics, SCFA production, and interactions with dietary fiber substrates was critically evaluated. Available in vivo studies indicate that short-term kefir supplementation is associated with shifts in canine gut microbiota composition, including increased lactic acid bacteria and reduced relative abundance of specific taxa, without adverse clinical effects. In vitro fermentation studies further suggest that fecal microbiota from kefir-fed dogs exhibit enhanced fermentation efficiency, lower pH, and increased SCFA production across various dietary fiber substrates. These findings imply that kefir may modulate not only microbial composition but also functional metabolic capacity. Collectively, current evidence supports the potential of kefir as a functional ingredient capable of modulating gut microbial fermentation in dogs. When combined with moderately fermentable dietary fibers, kefir-based synbiotic strategies may represent a promising approach for next-generation functional pet foods. However, standardization of microbial composition, quality control, and long-term clinical validation are required before broader commercial application.
Chon et al. (Sun,) studied this question.