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

膳食淀粉是单胃物种的一种迷人的营养素。该范例是，由于成熟猪的理化特性的变化，从低直链淀粉到高直链淀粉的淀粉范围从在上消化道中快速消化到在下消化道中可发酵。因此，淀粉可以是葡萄糖或短链脂肪酸（SCFA）的来源。我们惊讶地发现，在我们的研究中，即使在仔猪中也会发生大量的淀粉发酵;然而，断奶后的发育模式仍不清楚。在猪营养学中，可发酵淀粉被认为是一种负面的饮食因素，因为它会发酵并抑制全身营养物质的利用。相比之下，可发酵淀粉或抗性淀粉由于其抑制营养吸收速率和刺激肠道健康而在人类营养中越来越受欢迎。在仔猪中，整个肠道从代谢可快速消化的淀粉转变为可发酵的淀粉的潜在机制知之甚少，包括营养转运蛋白、化学传感器、肠道结构和渗透性以及向胰腺的肠促胰岛素信号传导的变化。这一假说认为，仔猪的淀粉从低直链淀粉逐渐转变为高直链淀粉，从而使仔猪逐渐从淀粉消化器转变为淀粉发酵器。这种变化引起肠道下游的潜在机制，通过肠道转运蛋白（葡萄糖与SCFA）、肠道内分泌反应（高血糖指数与低血糖指数）和微生物种群的变化来管理增加的淀粉流，并改变营养物质的利用和沉积。为了阐明机制变化，将使用幼龄猪模型，包括1）回肠插管以收集回肠，2）安乐死以收集肠组织和回肠，以及3）间接量热法。该组合允许测量整个胃肠道的淀粉消化的总程度和部位以及全身营养物质的使用和沉积。此外，SCFA和其他代谢物和肠激素的浓度可以作为生产指标进行测量。最后，可以研究淀粉流对维持肠道结构的影响以及未消化淀粉对微生物种群的影响。幼猪模型和纯化的膳食淀粉的组合在物理化学性质上是独特的，并且是研究淀粉及其代谢物的流动动力学及其对消化生理发育的影响的强大工具。这项工作加强了我们将膳食碳水化合物与广泛的营养和生理变量联系起来的努力，并评估了碳水化合物对全身营养素利用和沉积的负面和正面影响。这项工作对于更好地管理家畜物种中的营养流非常重要。最后，这项工作促进了对谷物和豆类中所含碳水化合物的破碎和表征，为加拿大农业食品工业创造了机会。

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.