Indices of gut health and intestinal microbial ecology of the cat as affected by ingestion of select carbohydrates varying in fermentative capacity

The focus of this research was to determine the impact of select fermentable carbohydrates on gastrointestinal health outcomes and microbial ecology of domestic cats. Four studies were designed to address two major research objectives: 1) to determine nutrient digestibility and fecal fermentative end-product outcome variables as affected by inclusion of select dietary fiber and fermentable carbohydrate sources, and 2) to determine the microbiome and metagenome of the feline gastrointestinal tract as they relate to fiber and fermentable carbohydrate supplementation. Study 1 determined the effects of supplementing oligofructose or a blend of oligofructose and inulin at 1% of the diet on nitrogen balance, fecal fermentative end-products, and select fecal microbiota of the senior cat. Study 2 determined the effects of supplementing cellulose, fructooligosaccharides (FOS), or pectin at 4% of the diet on total tract nutrient digestibility, fecal fermentative end-products, and select fecal microbiota of the young adult cat. Study 3 determined the effects of adapting the gastrointestinal microbiota to cellulose, FOS, or pectin at 4% of the diet on in vitro fermentation outcomes such as pH, gas production, short- chain fatty acid (SCFA) production and branched-chain fatty acid (BCFA) production. Study 4 determined the phylogeny and metabolic functional capacity of the feline fecal microbiome as affected by 4% supplemental cellulose, FOS, or pectin. Our results indicate that, in senior cats, supplemental FOS did not alter nitrogen metabolism, but influenced fermentative end-products. Fructooligosaccharides and pectin are capable of modulating fermentation end-products, and increased fecal score and SCFA, BCFA, ammonia, 4-methyl phenol, indole, and biogenic amine concentrations. Pectin also decreased crude protein and acid hydrolyzed fat digestibility, indicating that it may increase intestinal chyme viscosity and should be investigated further as a fermentable alternative to cellulose in weight loss diets. Adaptation to dietary FOS and pectin affected fermentation responses to cellulose, FOS, and pectin in vitro, but adaptation to FOS appeared to have the greatest effect on modulating these responses when FOS was utilized as a test substrate. This indicates that in vitro outcome variables are affected by fermentable substrates in the cat diet, and should be considered prior to initiating an in vitro experiment. Gastrointestinal microbiota were not affected greatly by the addition of 4% fiber or fermentable carbohydrate to the diet. However, specific metabolic functions and carbohydrate-active enzymes were impacted by the presence of fermentable substrates in the colon. Fiber source appears to impact physiological outcome variables in the cat, and future research studies should consider the impact of clinically-diagnosed disease states or highly varied diets (e.g., raw vs. extruded; high calorie vs. calorie-restricted) on microbial outcomes in the cat