Regulation of nitrogen salvage in non-ruminants

猪和其他非反刍动物能够通过尿素循环和随后在胃肠道中产生微生物氨基酸的过程来回收氮。然而，尿素再循环进入肠道的调节机制以及影响尿素再循环程度和随后的氮利用的因素(例如，饮食、生理)还不是很清楚。在反刍动物中，已证明尿素进入瘤胃的部分原因是由于尿素转运蛋白(UT-B和水通道蛋白)的易化，以及非特异性的细胞旁运动。膳食因素，如纤维和蛋白质摄入量，可能通过改变肠道环境和改变动物和寄生微生物的营养供应来影响氮的回收。假设尿素循环和氮素回收是一个受调控的过程，可以通过改变饮食中蛋白质和纤维的摄入量来控制。目的是确定(I)饲料组成(例如蛋白质和纤维含量)对尿素循环程度和再循环尿素去向的影响，(Ii)尿素通过肠壁运输的机制和调节，(Iii)饲料组成对非反刍动物氮素利用的影响，以及(Iv)饲料蛋白质波动对氮素利用和滞留的影响。为了实现这些目标，将招募一名博士生、4名硕士研究生和一名理科荣誉学位论文学生来完成一系列在猪身上的动物实验，猪是一种重要的农业动物物种。将使用同位素注入、生长性能、氮平衡和体外(例如，Ussing小室)技术的组合。该研究计划将为调节非反刍动物体内尿素循环和氮素回收的机制提供新的信息，这将导致开发新的饲养计划，以提高猪肉生产的氮素存留率和可持续性。这项研究计划的目标将有利于我的长期研究目标，即确定饲料成分和动物生理的相互作用，以便更好地了解这些因素对动物生长和健康的营养利用的影响。

Pigs and other non-ruminant animals are capable of salvaging nitrogen through the process of urea recycling and subsequent microbial amino acid production in the gastrointestinal tract. However, the regulatory mechanisms for urea recycling into the gut and the factors (e.g., dietary, physiological) influencing the extent of urea recycling and subsequent nitrogen utilization are not well understood. In the ruminant, it has been shown that urea transport into the rumen is due, in part, to facilitative urea transporters (UT-B and aquaporins) in addition to non-specific paracellular movement. Dietary factors, such as fibre and protein intake, may influence nitrogen salvage through altering the gut environment and changes in nutrient supply to the animal and resident microbes. The hypothesis is that urea recycling and nitrogen salvage is a regulated process that can be manipulated through changes in dietary protein and fibre intake. The objectives are to determine (i) the effect of diet composition (e.g., protein and fibre content) on extent of urea recycling and fate of recycled urea, (ii) the mechanism and regulation of urea transport across the gut wall, (iii) effect of diet composition on nitrogen utilization in the non-ruminant, and (iv) the effect of oscillating dietary protein on nitrogen utilization and retention. To address these objectives, a PhD student, 4 MSc students, and a BSc Honours thesis student will be recruited to complete a series of animal experiments in pigs, an agricultural important animal species. A combination of isotope infusion, growth performance, nitrogen-balance, and in vitro (e.g., Ussing chamber) techniques will be used. The proposed research program will provide novel information on the mechanisms regulating urea recycling and nitrogen salvage in the non-ruminant animal which will lead to the development of novel feeding programs to improve nitrogen retention and sustainability of pork production. The objectives of this research program will benefit my long-term research objective to characterize the interaction of feed components and animal physiology in order to better understand the impact of these factors on nutrient utilization for animal growth and health.