Prebiotics induce changes in the population and metabolic characteristics of the gastrointestinal bacteria, modulate enteric and systemic immune functions, and provide laboratory rodents with resistance to carcinogens that promote colorectal cancer. There is less known about protection from other challenges. Therefore, mice of the B6C3F1 strain were fed for 6 wk a control diet with 100 g/kg cellulose or one of two experimental diets with the cellulose replaced entirely by the nondigestible oligosaccharides (NDO) oligofructose and inulin. From each diet, 25 mice were challenged by a promoter of colorectal cancer (1,2-dimethylhydrazine), B16F10 tumor cells, the enteric pathogen Candida albicans (enterically), or were infected systemically with Listeria monocytogenes or Salmonella typhimurium. The incidences of aberrant crypt foci in the distal colon after exposure to dimethylhdrazine for mice fed inulin (53%) and oligofructose (54%) were lower than in control mice (76%; P < 0.05), but the fructans did not reduce the incidence of lung tumors after injection of the B16F10 tumor cells. Mice fed the diets with fructans had 50% lower densities of C. albicans in the small intestine (P < 0.05). A systemic infection with L. monocytogenes caused nearly 30% mortality among control mice, but none of the mice fed inulin died, with survival intermediate for mice fed oligofructose. Mortality was higher for the systemic infection of S. typhimurium (>80% for control mice), but fewer of the mice fed inulin died (60%; P < 0.05), with mice fed oligofructose again intermediate. The mechanistic basis for the increased resistance provided by dietary NDO was not elucidated, but the findings are consistent with enhanced immune functions in response to changes in the composition and metabolic characteristics of the bacteria resident in the gastrointestinal tract.

Secretions in the gastrointestinal tract proximal to the duodenum, enzymes in milk, and other digestive mechanisms compensate for low luminal activities of pancreatic enzymes during the perinatal period. Postnatal changes in digestive secretions influence nutrient availability, concentrations of signaling molecules, and activity of antimicrobial compounds that inhibit pathogens. Matching sources of nutrients to digestive abilities will improve the health of dogs during development.

The densities and metabolic characteristics of the gastrointestinal tract bacteria are responsive to dietary supplements of nondigestible oligosaccharides (NDO), but little is known about the in uences on the small intestine. Therefore, the colonic bacteria and the dimensions and transport functions of the small intestine were compared among mice (B6C 3F1 strain) fed diets with 10% cellulose (control) or with the cellulose replaced entirely with the NDO inulin or oligofructose or partially (2.5% oligofructose and 7.5% cellulose). Mice fed diets with 10% inulin or oligofructose had higher densities of anaerobes, aerobes, bacteroides, and lactobacilli, and lower proportions of enterics than mice fed a diet with 10% cellulose. Inulin, but not oligofructose, resulted in higher densities of streptococci. The small intestine was longer and weighed more when mice were fed 10% inulin with intermediate values for 10% oligofructose. Relative to control mice, rates of glucose transport and absorption of leucine, proline and glycyl-sarcosine (nmol:mg-min) were lower when mice were fed diets with 10% oligofructose and inulin, whereas only leucine was lower when mice were fed the diet with 2.5% oligofructose. Our ndings indicate supplementing diets with the NDO oligofructose and inulin 1) change the assemblages of colonic bacteria, 2) in uence the dimensions and absorptive functions of the small intestine, and 3) may be useful for managing the gastrointestinal ecosystem, but 4) the speci c responses vary among the types and amounts of NDO and among animal models.