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

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 <i>Enterococcus faecium</i> 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 <i>Enterococcus faecium</i> 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 <i>Enterococcus</i> spp. ASV, likely representing <i>E. faecium</i> NCIMB 10415 was detected in the faecal microbiome of some dogs 18-19 days after withdrawal of oral supplementation. Inclusion of <i>E. faecium</i> decreased circulating cholesterol (<i>p</i> = 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 <i>Fusobacterium</i>, <i>Streptococcus</i>, <i>Blautia</i>, and <i>Peptoclostridium</i>. Except for effects on circulating cholesterol and faecal score, effects were observed regardless of the addition of <i>E. faecium</i>. It is therefore likely that these effects can be contributed to dietary prebiotic effects on the faecal microbiome.