Lu Zhongyan, Shen Hong, Shen Zanming
Key Laboratory of Animal Physiology and Biochemistry, College of Veterinary Medicine, Nanjing Agricultural University, Nanjing, China.
College of Life Sciences, Nanjing Agricultural University, Nanjing, China.
Front Physiol. 2019 Aug 22;10:1079. doi: 10.3389/fphys.2019.01079. eCollection 2019.
Two experiments were performed in this study. In Experiment 1, twenty goats were fed with an isonitrogenous diet, containing 28% Non-Fiber Carbohydrate (MNFC group, = 10) or 14% NFC (LNFC group, = 10). In the MNFC group, the ruminal concentration of Short Chain Fatty Acids (SCFA) increased, and pH declined. Compared with those in the LNFC group, the microbial protein synthesis in rumen and mRNA abundance of urea transporter B (UT-B) in rumen epithelium increased in the MNFC group, although serum urea-N (SUN) did not differ significantly between groups. Simultaneously, urinal urea-N excretion was reduced in the MNFC group. Significant correlations were found between rumen SCFA and UT-B and between UT-B and urinal urea-N excretion. Furthermore, the abundances of SCFA receptor of GPR41 and GPR43 increased in the rumen epithelium of the MNFC group. These results suggest that increases of SUN transported into the rumen and incorporated into microbial protein and decreases of urinal urea-N excretion are related to ruminal SCFA. This is supported by data from our previous study in which added SCFA on the mucosal side caused increases of urea transport rate (flux J urea) from the blood to the ruminal lumen side. In Experiment 2, we used 16S rRNA Amplicon Sequencing to analyze the structure of the ruminal microbiota community in relation to SCFA. An additional eight goats were assigned into the MNFC ( = 4) and LNFC ( = 4) groups. The dietary ingredients, chemical composition, and feeding regimes were the same as those in Experiment 1. Constrained correspondence analysis (CCA analysis) revealed NFC promoted the expansion of microbiota diversity, particularly of SCFA-producing microbes. The function prediction of 19 upregulated Kyoto Encyclopedia of Genes and Genomes (KEGG) ortholog groups showed an NFC-induced increase of the types and abundances of genes coding for enzymes catalyzing N and fatty acid metabolism. Based on our present and previous investigations, our results indicate that, in goats consuming a MNFC diet, the facilitated urea transport in the rumen and improved urea N salvage are triggered by an expansion of ruminal microbiota diversity and are signaled by ruminal SCFA. This study thus provides new insights into the microbiota involved in the dietary modulation of urea-N salvage in ruminant animals.
本研究进行了两项实验。在实验1中，给20只山羊饲喂等氮日粮，其中一组日粮含有28%的非纤维碳水化合物（MNFC组，n = 10），另一组含有14%的非纤维碳水化合物（LNFC组，n = 10）。在MNFC组中，瘤胃短链脂肪酸（SCFA）浓度升高，pH值下降。与LNFC组相比，MNFC组瘤胃微生物蛋白合成增加，瘤胃上皮尿素转运体B（UT - B）的mRNA丰度升高，尽管两组间血清尿素氮（SUN）无显著差异。同时，MNFC组尿尿素氮排泄减少。瘤胃SCFA与UT - B之间以及UT - B与尿尿素氮排泄之间存在显著相关性。此外，MNFC组瘤胃上皮中GPR41和GPR43的SCFA受体丰度增加。这些结果表明，进入瘤胃并掺入微生物蛋白中的SUN增加以及尿尿素氮排泄减少与瘤胃SCFA有关。我们之前的研究数据支持了这一点，在之前的研究中，在黏膜侧添加SCFA会导致从血液到瘤胃腔侧的尿素转运速率（通量J尿素）增加。在实验2中，我们使用16S rRNA扩增子测序分析与SCFA相关的瘤胃微生物群落结构。另外8只山羊被分为MNFC组（n = 4）和LNFC组（n = 4）。日粮成分、化学组成和饲养方式与实验1相同。受限对应分析（CCA分析）显示，非纤维碳水化合物促进了微生物群落多样性的扩展，特别是产SCFA微生物的多样性。对19个上调的京都基因与基因组百科全书（KEGG）直系同源组的功能预测表明，非纤维碳水化合物诱导了编码催化氮和脂肪酸代谢酶基因的类型和丰度增加。基于我们目前和之前的研究，我们的结果表明，在采食MNFC日粮的山羊中，瘤胃中尿素转运的促进和尿素氮回收的改善是由瘤胃微生物群落多样性的扩展引发的，并由瘤胃SCFA发出信号。因此，本研究为反刍动物日粮中尿素氮回收的饮食调节所涉及的微生物群提供了新的见解。
