Abstract：
Long-term feeding of a high-concentrate diet can induce subacute ruminal acidosis (SARA) in ruminants, which further leads to systemic inflammatory response. However, few studies have examined the effects of feeding a high-concentrate diet on the hindgut of ruminants. The purpose of this study was to investigate the effects of a high-concentrate diet on the composition of gut microbiota in colonic contents, inflammatory response, and barrier damage in the colon tissue of ruminants. A total of 12 healthy multiparous lactating Hu sheep were randomly allotted into the following 2 groups: a high-concentrate (HC) group (concentrate:forage = 7:3) and a low-concentrate (LC) group (concentrate:forage = 3:7). All sheep were fitted with ruminal fistulas. The formal feeding experiment lasted for 8 wk. After the feeding experiment, rumen fluid, portal vein blood, hepatic vein blood, colonic contents, and colon tissue samples were collected. The results showed that feeding the HC diet induced SARA in Hu sheep and significantly reduced pH in the colonic contents. The abundances of Firmicutes, Verrucomicrobiota, and Actinobacteriota decreased significantly, whereas those of Bacteroidota, Spirochaetota, and Fibrobacterota significantly increased in colonic contents. At the genus level, the relative abundances of 29 genera were significantly altered depending on the different type of diets. Analysis of the 10 bacterial genera with high relative abundance revealed that feeding the HC diet significantly reduced the abundance of UCG-005, Christensenellaceae R-7 group, UCG-010-norank, Monoglobus, [Eubacterium] coprostanoligenes group_norank, and Alistipes, whereas the abundances of Rikenellaceae RC9 gut group, Treponema, Bacteroides, and Prevotella increased. Compared with the LC group, feeding the HC diet significantly increased the concentration of LPS in rumen fluid, portal vein blood, hepatic vein blood, and colonic contents, and significantly upregulated the mRNA expression levels of proinflammatory cytokines in colon tissue, including TNF-α, IL-1β, IL-6, and IL-8, indicating the occurrence of inflammatory response in the colon tissue. In addition, the structure of colonic epithelial cells was loose, the intercellular space became larger, epithelial cells were exfoliated, and the mRNA and protein abundances of ZO-1, occludin, claudin-1, claudin-3, and claudin-4 were significantly decreased in the HC group, which was consistent with the results of immunohistochemistry. Furthermore, feeding the HC diet increased the ratios of DNA methylation and chromatin compaction in the promoter regions of occludin and claudin-1, which in turn inhibited their transcriptional expression. Therefore, the present study demonstrated that feeding an HC diet induced SARA in Hu sheep, altered the composition and structure of the microbial community in the colonic contents, induced an inflammatory response, and disrupted the intestinal mucosal barrier in the colonic tissue.
摘要：
长期饲喂高浓度饮食可诱发反刍动物亚急性瘤胃酸中毒(SARA),这进一步导致全身炎症反应。然而,很少有研究研究了饲喂高浓度饮食对反刍动物后肠的影响。这项研究的目的是研究高浓缩饮食对结肠内容物中肠道菌群组成的影响。炎症反应，反刍动物结肠组织的屏障损伤。将12只健康的多胎泌乳湖羊随机分为以下2组：高浓度（HC）组（浓缩物：牧草=7：3）和低浓度（LC）组（浓缩物：牧草=3：7）。所有绵羊都装有瘤胃瘘。正式喂养实验持续了8周。饲喂实验后，瘤胃液,门静脉血，肝静脉血,结肠内容物,收集结肠组织样品。结果表明，饲喂HC日粮在湖羊中诱导了SARA，并显着降低了结肠含量的pH。Firmicutes的丰富，Verrucomicrobiota,放线菌明显减少，而那些拟杆菌，Spirochaetota,纤维杆菌的结肠含量显着增加。在属一级，根据不同的饮食类型，29属的相对丰度发生了显着变化。对具有高相对丰度的10个细菌属的分析表明，饲喂HC饮食显着降低了UCG-005，ChristenellaceaeR-7组的丰度，UCG-010-norank,Monoglobus,[Eubacterium]coprostanolidgenesgroup_norank,和Alistipes,而RikenellaceaeRC9肠组的丰度，密螺旋体,拟杆菌,普雷沃氏菌增加了。与LC组相比，饲喂HC饮食显著增加了瘤胃液中LPS的浓度，门静脉血，肝静脉血,和结肠内容物，显著上调结肠组织中促炎细胞因子的mRNA表达水平,包括TNF-α,IL-1β,IL-6和IL-8，表明结肠组织中炎症反应的发生。此外,结肠上皮细胞结构疏松,细胞间空间变得更大，上皮细胞脱落，以及ZO-1，occludin的mRNA和蛋白质丰度，HC组claudin-1、claudin-3和claudin-4显著降低,这与免疫组织化学结果一致。此外，饲喂HC饮食增加了occludin和claudin-1启动子区域的DNA甲基化和染色质压缩的比率，从而抑制了它们的转录表达。因此,本研究表明，饲喂HC饮食在湖羊中诱导SARA，改变了结肠内容物中微生物群落的组成和结构，诱导炎症反应，并破坏结肠组织的肠粘膜屏障。
