Table 1. Summary of in vivo and in vitro studies evaluating kefir-related interventions and their effects on gut microbiota and fermentation characteristics in dogs

Study type	Subjects (condition)	Duration	Intervention	Primary endpoints	Key findings	References
In vivo study	Healthy adult dogs	2 weeks	Kefir supplementation	Gut microbiota composition (LAB abundance, F/B ratio), clinical signs	↑ Lactic acid bacteria;↓ F/B ratio; no adverse clinical effects	[10]
Product analysis	Commercial pet kefir products	–	Microbial composition & CFU enumeration	Labeled vs. detected microbes; viable cell counts	Discrepancy between label and actual composition; high variability in CFU	[11]
In vitro fecal fermentation	Fecal inoculum from dogs with kefir history	Incubation period (in vitro)	Dietary fiber fermentation assay	SCFA production; pH change	↑ SCFA production; greater pH reduction (enhanced fermentation efficiency)	[12]
In vitro fecal fermentation (post-antibiotic)	Fecal inoculum from dogs treated with metronidazole	Incubation period (in vitro)	Fermentation assay	SCFA production; fermentation capacity	↓ Fermentation capacity and SCFA production (functional impairment post-antibiotic)

CFU, colony forming unit; LAB, lactic acid bacteria; F/B ratio, firmicutes/bacteroidetes; SCFA, short-chain fatty acid.