Effects of Bacillus coagulans (GBI-30, 6086) Supplementation on the Fecal Characteristics and Microbiota of Healthy Adult Dogs Subjected to an Abrupt Diet Change

Studies in humans and livestock have demonstrated <i>Bacillus coagulans</i> GBI-30, 6086 to have probiotic potential, suggesting that it may alleviate gastrointestinal (GI) distress commonly associated with diet change in dogs. This study aimed to evaluate the effects of <i>B. coagulans</i> GBI-30, 6086 on fecal scores, pH, dry matter (DM) percentage, and microbiota populations of dogs following an abrupt diet change. English Pointer dogs (<i>n</i> = 12; age = 5.9 ± 2.5 yr; body weight = 26.6 ± 6.1 kg) were used in a replicated 3 × 3 Latin square design and fed commercial diets containing no probiotics or prebiotics. The following treatments were administered orally in gelatin capsules before each daily feeding: (1) placebo control (250 mg maltodextrin/day); (2) <i>B. coagulans</i> [low dose; 5 × 10⁸ colony-forming units (CFU)/day]; and (3) <i>B. coagulans</i> (high dose; 2.5 × 10⁹ CFU/day). An extruded kibble diet was fed for 28 days. Dogs were then abruptly switched to a canned diet and fed for 14 days, with fecal samples collected before and 2, 6, 10, and 14 days after diet change. All data were analyzed using the Mixed Models procedure of SAS 9.4, testing the effects of treatment, time, and treatment*time interactions. Treatment*time interactions were not observed, but the abrupt diet change reduced (<i>p</i> < 0.0001) fecal DM content, increased (<i>p</i> < 0.0001) fecal scores and pH, and reduced (<i>p</i> < 0.0001) fecal bacterial species richness and phylogenetic diversity. Diet change also increased (<i>p</i> < 0.001) fecal Bacteroidota, Fusobacteriota, and Proteobacteria, decreased (<i>p</i> < 0.001) fecal Firmicutes, and altered ~40 fecal bacterial genera relative abundances. Diet-induced changes were minimally impacted by <i>B. coagulans</i>, but fecal scores tended to be lower (i.e., firmer stools; <i>p</i> < 0.10), fecal <i>E. coli</i> and <i>Faecalibacterium</i> abundances were greater (<i>p</i> < 0.05), and fecal bacterial phylogenetic diversity was higher (<i>p</i> < 0.05) in dogs supplemented with the low dose than in controls. Our results demonstrate that abruptly transitioning dogs from a kibble to a canned diet negatively influences fecal characteristics and considerably shifts the composition of the fecal microbiota. Supplementation with <i>B. coagulans</i> did not mitigate the diet-induced shifts to fecal characteristics and most of the microbial taxa, although the low dose impacted some microbial taxa. Further investigation into optimal inclusion levels in pet foods is warranted.