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

对于单胃动物来说，膳食淀粉是一种令人着迷的营养物质。由于成熟猪的物理化学特性的变化，直链淀粉从低到高的范围从上肠的快速消化到下肠的可发酵。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，即使在幼猪大量淀粉发酵可以发生；然而，断奶后的发育模式仍不清楚。在猪营养研究中，可发酵淀粉被认为是一种不利的饲粮因子，因为它对猪全身营养物质的利用具有抑制作用。相比之下，可发酵或抗性淀粉由于其抑制营养吸收速度和刺激肠道健康而在人类营养中越来越受欢迎。仔猪肠道从代谢快速消化淀粉转变为可发酵淀粉的潜在机制尚不清楚，包括营养转运体、化学传感器、肠道结构和通透性的变化，以及肠促胰岛素向胰腺的信号传导。假设是直链淀粉从低到高的逐渐转变使仔猪逐渐从淀粉消化器转变为淀粉发酵器。这种变化触发了肠道下游的潜在机制，通过肠道转运体（葡萄糖vs. SCFA）、肠道内分泌反应（高血糖指数vs.低血糖指数）和微生物种群的变化来管理淀粉流的增加，并改变了营养物质的利用和沉积。为阐明其机制变化，将采用回肠插管收集食糜、安乐死收集肠组织和食糜、间接量热法等方法建立仔猪模型。该组合可以测量整个胃肠道淀粉消化的总程度和部位以及全身营养物质的利用和沉积。此外，SCFA和其他代谢物以及肠道激素的浓度可以作为生产指标进行测量。最后，可以研究淀粉流量对肠道结构维持的影响以及未消化淀粉对微生物种群的影响。仔猪模型与纯化饲粮淀粉在理化性质上的结合是独特的，是研究淀粉及其代谢物流动动力学及其对消化生理发育影响的有力工具。这项工作加强了我们将膳食碳水化合物与一系列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利用和沉积的消极和积极影响。这项工作对更好地管理家畜物种的营养流动具有重要意义。最后，这项工作促进了对谷物和豆类谷物中碳水化合物的分离和表征，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.