Mannan from yeast has been demonstrated to limit infection in animals susceptible to gastrointestinal infection, including pigs, poultry and cows, by blocking the mechanism by which gram-negative bacteria adhere to and invade the intestines. Enterotoxigenic Escherichia coli (ETEC) cause post weaning diarrhoea (PWD) which results in poor weight gain and potential death at great economic cost to the farmer. A mannan rich fraction (MRF) was assessed in vitro for its impact on ETEC infection of HT-29 intestinal cell line. Gene expression markers for inflammation (TNFα and IL-1β) and TLR4 (TICAM-1 and LY96) associated recognition of bacteria were significantly elevated following exposure to E. coli alone, but not in combination with MRF compared to the control. HT-29 cells exposed to MRF alone demonstrated significantly reduced expression of immune signalling genes IRAK1, IRF7 and JUN when compared to the control. HT-29 cell protein abundance for TNFα and TLR4 associated proteins were significantly increased in response to E. coli exposure alone while no significant change was observed for MRF treatment with E. coli infection. E. coli adhesion to HT-29 cells was significantly decreased with addition of MRF compared to E. coli infection alone. The action of MRF demonstrated its potential capacity to limit infection on an in vitro level through blocking bacterial interaction with the intestines that leads to infection as marked by a reduction in proinflammatory responses. MRF on its own demonstrated potential anti-inflammatory effects on intestinal cells with the reduction of proinflammatory responses observed.

The physiological role of the gastrointestinal microbiota has become an important subject of nutrition research in pigs in the past years, and the importance of intestinal microbial activity in the etiology of disease is doubtless. This review summarizes the recent knowledge related to the microbial ecology of protein fermentation and the appearance of protein-derived metabolites along the pig intestine. The amount of fermentable protein depends on factors such as dietary protein concentration, protein digestibility due to secondary or tertiary structure, the interaction with dietary compounds or anti-nutritional factors, and the secretion of endogenous proteins into the gut lumen. High protein diets increase the luminal concentrations and epithelial exposure to putatively toxic metabolites and increase the risk for post-weaning diarrhea, but the mechanisms are not yet clarified. Although the use of fermentable carbohydrates to reduce harmful protein-derived metabolites in pigs is well-established, recent studies suggest that the inclusion of fermentable carbohydrates into diets with low protein digestibility or high dietary protein level may not ameliorate all negative effects with regard to epithelial response. Based on the current knowledge, the use of diets with low levels of high-quality protein may help to reduce the risk for intestinal disease in young pigs.