PSIX-3 - A veterinary gastrointestinal low-fat diet affects fecal characteristics, metabolites, bile acids, and microbiota concentrations of antibiotic-treated dogs

Abstract: In a recent dog study, the antibiotic metronidazole proved to be an effective disruptor of the fecal microbiota and resulted in looser stools and altered fecal bile acid (BA) profiles. Recovery took several weeks and was aided by a dietary supplement. The objective of this study was to determine how a veterinary gastrointestinal low-fat diet affected the fecal characteristics and metabolite, BA, and microbiota concentrations of dogs recovering from metronidazole administration. Twenty-four healthy adult dogs were used in an 8-wk completely randomized design study. The study began with a 2-wk baseline phase where all dogs consumed a leading grocery brand dry kibble diet (GBD; wk0-wk2). Over the next 2 wk, dogs continued to consume GBD and received metronidazole (20 mg/kg BW) (wk2-wk4). At wk 4, dogs were randomly allotted to one of two treatments [GBD; Blue Buffalo Gastrointestinal Support Low-Fat (BB)] for the remaining 4 wk (wk5-wk8). Fecal scores were recorded daily and fresh fecal samples were collected at wk 2, 4, 5, 6, 7, and 8 for measurement of pH, dry matter, and metabolite and bile acid concentrations. Fecal microbiota populations were also analyzed by 16S rRNA sequencing and qPCR, which was used to calculate dysbiosis index. All data were analyzed as repeated measures using the Mixed Models procedure of SAS 9.4, with treatment treated as a fixed effect, dog as a random effect, and significance set at P< 0.05. As anticipated, metronidazole administration increased (P< 0.0001) fecal scores (looser stools) and drastically altered (P< 0.05) fecal metabolite concentrations, reducing fecal short-chain fatty acid (SCFA), branched-chain fatty acid (BCFA), phenol, and indole concentrations, increasing primary BA concentrations, and decreasing secondary bile acid concentrations. Metronidazole dramatically impacted fecal microbiota populations by reducing alpha diversity, altering the abundance of multiple bacterial taxa, and increasing dysbiosis index. Fecal outcome variables recovered over the next 4 wk, with some being impacted by diet. The change in fecal SCFA and immunoglobulin A concentrations were higher (P< 0.01), while the change in fecal BCFA, phenol, and indole concentrations were lower (P< 0.05) in dogs fed BB. Dysbiosis index and alpha diversity measures recovered quickly for all dogs and without dietary effects. Recovery of over 25 bacterial genera were impacted by diet (P< 0.05). While many bacterial taxa returned to baseline levels after 4 wk, others had still not fully recovered. Fecal BA concentrations recovered quickly for all dogs. The change in lithocholic acid concentration was lower (P< 0.0001) in dogs fed BB, but other BA concentrations were not affected by diet. In conclusion, metronidazole drastically alters the fecal microbiota and metabolites of dogs. While most variables return to normal over time, a veterinary gastrointestinal diet may aid in the recovery.