Impact of physico-chemical properties of dietary starch on digestive physiology in young pigs

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Dietary starch is a fascinating nutrient for monogastric species. The paradigm is that starches ranging from low to high amylose range from rapidly digestible in the upper gut to fermentable in the lower gut due to changes in physico-chemical characteristics in mature pigs. Starch can thus be a source of glucose or short-chain fatty acids (SCFA). We were surprised to discover in our research that even in young pigs substantial starch fermentation can occur; however, developmental patterns following weaning remain unclear. In swine nutrition, fermentable starch is considered a negative dietary factor due to its fermentation and suppressive effects on whole body nutrient utilization. In contrast, fermentable or resistant starch is gaining popularity in human nutrition due to its suppression of rate of nutrient absorption and stimulation of intestinal health. The underlying mechanisms throughout the intestine to change from metabolizing rapidly digestible starch to fermentable starch are poorly understood in the young pig, including changes in nutrient transporters, chemo-sensors, gut structure and permeability, and incretin signaling to the pancreas. The hypothesis is that a gradual shift from low to high amylose starch changes the young pig gradually from starch digester into starch fermenter. This change invokes underlying mechanisms downstream in the gut to manage the increased starch flow via changes in intestinal transporters (glucose vs. SCFA), intestinal endocrine responses (high vs. low glycemic index), and microbial populations, and alters nutrient utilization and deposition. To clarify the mechanistic changes, young pig models including 1) ileum cannulation to collect digesta, 2) euthanasia to collect intestine tissue and digesta, and 3) indirect calorimetry will be used. The combination allows measuring of total extent and site of starch digestion throughout the gastro-intestinal tract and whole body nutrient use and deposition. Moreover, concentrations of SCFA and other metabolites and intestinal hormones can be measured as indicators of production. Finally, effects of starch flow on maintenance of intestinal structure and of non-digested starch on microbial populations can be studied. The combination of young pig models and purified dietary starches ranging in physico-chemical properties is unique and is a robust tool to study the kinetics of flow of starch and its metabolites, and their impact on development of digestive physiology. The work strengthens our efforts to link dietary carbohydrates to a wide array of nutritional and physiological variables, and assess negative and positive effects of carbohydrates on whole body nutrient utilization and deposition. The work is important to better manage nutrient flow in domestic animal species. Finally, the work stimulates efforts to fractionate and characterize carbohydrates contained in cereal and pulse grains, creating opportunities for Canadian agri-food industries.