Alterations in Healthy Adult Canine Faecal Microbiome and Selected Metabolites as a Result of Feeding a Commercial Complete Synbiotic Diet with Enterococcus faecium NCIMB 10415

Simple Summary Probiotics are defined as live microorganisms that, when administered in adequate amounts, confer a health benefit on the host. The effect of a commercial diet containing the probiotic Enterococcus faecium NCIMB 10415 was examined in a crossover study with 11 healthy privately owned dogs. The dogs were fed the same balanced commercial diet, with or without the probiotic, for 16 days, and then fed the alternate diet for an additional 16 days with a 19 days washout period in between. Owners evaluated their dog’s faecal quality daily. Faecal bacterial composition (microbiome) and short-chain fatty acid concentrations as well as serum concentrations of cholesterol, triglycerides, cobalamin and folate were analysed before and after each feeding period. Soft stools were less frequent when fed the diet with probiotic included compared with the diet alone. The probiotic diet also decreased serum cholesterol. Most observed effects were related to the diet itself, irrespective of probiotic inclusion or not. These effects included an increased faecal microbial diversity and content of the short-chain fatty acids butyrate and acetate, as well as a decrease in serum cobalamin concentration. There were indications of a likely prolonged survival (19 days) of the probiotic strain in a few individual dogs, which has not previously been reported for this probiotic strain. Abstract In dogs, the use of probiotics for preventive or therapeutic purposes has become increasingly common, however the evidence for beneficial effects are often limited. The aim of this study was to investigate the effects of feeding a diet containing Enterococcus faecium NCIMB 10415 on faecal quality, faecal short-chain fatty acid concentrations, serum concentrations of cholesterol, triglycerides, cobalamin and folate as well as faecal microbiome in adult dogs. Eleven healthy client owned dogs were enrolled in a randomized, double-blinded crossover study. All dogs were fed the same balanced diet with or without incorporation of Enterococcus faecium NCIMB 10415 for 16 days each. Blood and faecal samples were collected at baseline and during the feeding trial and owners recorded daily faecal scores. An Enterococcus spp. ASV, likely representing E. faecium NCIMB 10415 was detected in the faecal microbiome of some dogs 18–19 days after withdrawal of oral supplementation. Inclusion of E. faecium decreased circulating cholesterol (p = 0.008) compared to baseline. There were no differences in cholesterol concentrations between diets. Owners reported 0.6 ± 0.3) days less of loose stools compared to the control diet. Comparing to baseline, both diets significantly increased faecal concentration of acetate and butyrate, decreased serum cobalamin and increased faecal microbial diversity. Decreased serum cobalamin, and increased faecal acetate correlated with decreases in the Fusobacterium, Streptococcus, Blautia, and Peptoclostridium. Except for effects on circulating cholesterol and faecal score, effects were observed regardless of the addition of E. faecium. It is therefore likely that these effects can be contributed to dietary prebiotic effects on the faecal microbiome.