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

膳食淀粉对于单胃物种来说是一种令人着迷的营养物质。这种模式是，由于成熟猪的物理化学性质的变化，从低直链淀粉到高直链淀粉，从上肠道可快速消化到下肠道可发酵。因此，淀粉可以作为葡萄糖或短链脂肪酸(SCFA)的来源。我们在研究中惊讶地发现，即使在年轻的猪身上，也可以发生大量的淀粉发酵；然而，断奶后的发育模式仍然不清楚。在猪营养中，可发酵淀粉因其发酵和抑制全身营养物质的利用而被认为是一种负面的饲粮因素。相比之下，可发酵或抗性淀粉在人类营养中越来越受欢迎，因为它抑制了营养吸收速度，并刺激了肠道健康。幼猪肠道从快速可消化淀粉代谢转变为可发酵淀粉的潜在机制尚不清楚，包括营养转运体、化学感受器、肠道结构和通透性的变化，以及向胰腺传递的胰岛素信号。假说是，从低直链淀粉到高直链淀粉的逐渐转变使幼猪逐渐从淀粉消化器变成淀粉发酵器。这种变化激活了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量，并改变营养物质的利用和沉积。为了阐明这种机制的变化，将使用1)回肠插管收集消化液，2)安乐死收集肠组织和消化，3)间接量热法的幼猪模型。这一组合允许测量整个胃肠道和全身营养物质的利用和沉积的淀粉消化的总范围和位置。此外，SCFA和其他代谢物和肠道激素的浓度可以作为生产指标进行测量。最后，可以研究淀粉流动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。仔猪模型和精制饲料淀粉在理化性质上的组合是独特的，是研究淀粉及其代谢物流动动力学及其对消化生理学发展影响的有力工具。这项工作加强了我们努力将膳食碳水化合物与广泛的营养和生理变量联系起来，并评估碳水化合物对全身营养利用和沉积的消极和积极影响。这项工作对于更好地管理家畜物种中的营养流动非常重要。最后，这项工作刺激了对谷物和豆类谷物中所含碳水化合物进行分级和表征的努力，为加拿大的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.