Dietary supplementation with Bacillus subtilis C-3102 improves gut health indicators and fecal microbiota of dogs

This study aimed to evaluate the effects of Bacillus subtilis C-3102 on diet digestibility, fecal characteristics, and fecal microbiota of dogs. Sixteen adult Beagle dogs were randomly assigned to one of the two dietary treatments for 33 days: control (no B. subtilis C-3102, n = 8) and B. subtilis C-3102 (1 × 10⁶ CFU of B. subtilis C-3102/g of diet, n = 8). Diets were offered for an adaptation period of 28 days followed by five days of total fecal collection. The coefficients of total tract apparent digestibility (CTTAD) of nutrients and metabolizable energy (ME) content of diets were evaluated. Fecal characteristics were evaluated at the end of the study by dry matter content, fecal score (1 = watery to 5 = firm stools), pH, ammonia concentration, odor, short-chain fatty acids (SCFA), branched-chain fatty acids (BCFA), and sialic acid concentrations. The fecal odor was evaluated by 50 volunteers by comparing the odor of fresh feces of the B. subtilis C-3102 vs the control group. Fecal microbiota was evaluated by sequencing the 16S rRNA gene. No difference was observed between the groups for CTTAD and ME (P > 0.05). Likewise, no differences were observed for fecal pH and sialic acid (P > 0.05). However, firmer stools (P < 0.001), greater dry matter content (P = 0.021) and propionic acid concentration (P = 0.039) and lower fecal odor (P < 0.001) and ammonia (P = 0.037) were observed in dogs fed B. subtilis C-3102. The 16S rRNA gene sequencing revealed that the addition of B. subtilis altered gut microbiota of dogs. Proportional changes of gut microbiota between groups were detected in four major phyla and 13 genera of bacteria (P < 0.05). Gut bacterial diversity was greater (P = 0.025) in dogs fed B. subtilis C-3102. Among these changes, dogs fed B. subtilis C-3102 presented a greater abundance of bacterial groups, which are considered to be beneficial for gut health, such as Bacteroides, Faecalibacterium, and Allobaculum when compared to the control group (P < 0.05). Whereas the control group presented an increase in Bifidobacterium, Enterococcus, Clostridium sensu stricto 1, Lactobacillus, Anaerostipes, Escherichia-Shigella, Enterorhabdus, and Eubacterium brachy (P < 0.05). Overall, the data indicated that coating the diet with 1 × 10⁶ CFU of B. subtilis C-3102/g has positive effects on fecal characteristics and alters the fecal microbiota of dogs.