瘤胃尿素转运与代谢调控研究进展

doi:10.3864/j.issn.0578-1752.2015.S.010

摘要/Abstract

摘要： 瘤胃细菌具有水解尿素的能力，可将日粮中添加的外源尿素和经由血液循环进入瘤胃的内源尿素迅速水解成氨，为自身生长提供所需氮源。实际生产中，常以适量尿素替代部分日粮氮，以达到降低生产成本的目的。但是，奶牛日粮中尿素添加的推荐剂量存在上限，即小于等于精料的1%，约为每天135g/头，或者不超过日粮中总粗蛋白的20%。反刍动物肝脏合成的尿素中，约有40%—80%的尿素氮回流至胃肠道中，其中，35%—55%的氮参与瘤胃细菌的合成代谢。分布于瘤胃乳头上皮层的尿素转运蛋白是血液中的内源尿素向瘤胃内转运的主要载体，其尿素转运蛋白受瘤胃内氨浓度和血液中尿素浓度的影响调控内源尿素的转运。瘤胃中参与尿素代谢的细菌种类繁多，主要来源于厚壁菌门（Firmicutes）、放线菌门（Actinobacteria）和变形菌门（γ-Proteobacteria），此外，在未培养菌中也发现了大量的尿素分解菌。脲酶是瘤胃尿素代谢的关键限速酶，可催化尿素迅速水解成氨和二氧化碳。然而，瘤胃细菌水解尿素的速度是氨同化作用速度的4倍，瘤胃中尿素的快速水解将导致瘤胃细菌尿素氮利用效率的降低。瘤胃中过量的氨，穿过瘤胃壁进入血液将提高动物机体氨中毒的机率；或以尿氮或粪氮的形式排出动物机体造成氮素的浪费及对环境的污染。因此，研究瘤胃尿素转运与代谢调控在平衡反刍动物氮代谢和机体稳态中发挥着重要作用。论文重点综述了尿素在反刍动物日粮中的应用、内源尿素的转运载体、参与尿素代谢的瘤胃细菌种类、以及瘤胃细菌代谢尿素的生理机制和调控途径。

关键词: 瘤胃尿素分解菌, 尿素转运蛋白, 脲酶, 尿素代谢

Abstract: The urea from the diet or recycled from blood into rumen is hydrolyzed by ruminal bacteria to ammonia, which acts as the major source of nitrogen for many ruminal bacterial growth. Urea is usually used as a replacement for parts of dietary nitrogen in practice, for cost reduction. The common recommendation for urea addition is less than 1% of the concentrate portion of the diet, approximately 135 g/cow daily, or not more than 20% of total dietary crude protein. Around 40% to 80% of the urea nitrogen synthesized in the liver can return to the gastrointestinal tract, where approximately 35% to 55% of this nitrogen will take part in bacterial anabolism. Urea transporter, distributed in epithelial layer of rumen papillae, plays an important role in endogenous urea transport from blood to rumen, which is regulated by ammonia concentration in the rumen or urea concentration in the blood or the both. There are various ureolytic bacteria in the rumen, which belong to Firmicutes, Actinobacteria, γ-Proteobacteria, and uncultured bacteria. Urease is the key enzyme in the pathway of urea hydrolysis. Urea is rapidly hydrolyzed into ammonia and carbon dioxide by the catalysis of urease in the rumen. However, the rate of urea hydrolysis is about four times than that of ammonia assimilation, resulting in the reduction of urea utilization efficiency. The diffusion of excess ammonia into blood also lead to increasing chance of toxicity for ruminants. In addition, the excretion of residual ammonia in feces and urine possibly causes the environmental pollution. Thus, ruminal urea transporter, metabolism and its regulation play an important role in the nitrogen balance and body homeostasis of ruminants. This article mainly summarized the application of urea in the diets of ruminants, urea transporter, the taxa and diversity of rumen ureolytic bacteria, and the mechanism and regulation of urea metabolism by ruminal bacteria.

Key words: rumen ureolytic bacteria, urea transporter, urease, urea hydrolysis

王芃芃，郑楠，王加启，赵圣国. 瘤胃尿素转运与代谢调控研究进展[J]. 中国农业科学, 2015, 48(S): 86-93.

WANG Peng-peng, ZHENG Nan, Wang Jia-qi, ZHAO Sheng-guo. Progresses of Research on Ruminal Urea Transport, Metabolism and Its Regulation[J]. Scientia Agricultura Sinica, 2015, 48(S): 86-93.

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