Antibiotics are used to treat gastrointestinal diseases or infections but are known to negatively affect stool quality and gut microbiota in cats and dogs. Therefore, identifying dietary strategies that may aid in antibiotic recovery is of interest. The objective of this study was to determine how a veterinary gastrointestinal diet affected the fecal characteristics, microbiota, and metabolite and bile acid (BA) concentrations of cats recovering from metronidazole administration. Twenty-four healthy adult cats were used in an 8-wk completely randomized design study. During a 2-wk baseline, all cats consumed a leading grocery brand diet (GBD). Over the next 2 wk, cats consumed GBD and received metronidazole (20 mg/kg body weight twice daily). At week 4, cats were randomly allotted to one of 2 treatments [GBD; BLUE Natural Veterinary Diet GI Gastrointestinal Support (BB)] and fed for 4 wk. Fecal scores were recorded daily and fresh fecal samples were collected at weeks 2, 4, 5, 6, 7, and 8 for measurement of pH, dry matter (DM) %, metabolites, and microbiota. Microbiota was analyzed by 16S rRNA gene sequencing and qPCR, which was used to calculate dysbiosis index. Data were analyzed as repeated measures using the Mixed Models procedure of SAS 9.4, testing for effects of diet, time and diet*time. Metronidazole had dramatic effects on all outcomes, including increased fecal scores (looser stools), reduced fecal pH and DM%, reduced fecal short-chain fatty acid, branched-chain fatty acid, ammonia, phenol, and indole concentrations, and altered fecal BA concentrations (increased primary BA; reduced secondary BA). Metronidazole reduced fecal bacterial alpha diversity, increased dysbiosis index, and altered the relative abundance of 78 bacterial genera. Fecal outcomes partially recovered over the next 4 wk, with some being impacted by diet. Fecal acetate concentrations were higher after metronidazole in cats fed BB. Dysbiosis index and alpha diversity measures slowly recovered over 4 wk, without diet differences. Recovery of 16 bacterial genera was impacted by diet. Fecal BA profiles demonstrated a prolonged impairment of primary to secondary BA conversion, with cholic acid being lower after metronidazole in cats fed BB. In conclusion, our data demonstrate that metronidazole is a powerful antibiotic that has long-lasting effects on the fecal microbiota and metabolites of cats. Outcome variables slowly recovered over time, but a gastrointestinal diet may aid in recovery.
