高谷物日粮诱导的亚急性瘤胃酸中毒（SARA）会损害反刍动物的瘤胃上皮屏障功能，但SARA是否会持续性损害瘤胃上皮屏障的形态结构和功能还尚不清楚。本研究旨在以泌乳山羊为动物模型，研究SARA是否对瘤胃上皮的形态结构、通透性及参与上皮屏障功能的关键基因表达具有持续性影响。选取12只安装有永久性瘤胃瘘管的泌乳中期奶山羊，随机分为对照组（Ctrl，n=4）和SARA组（n=8），对照组试验动物饲喂NFC/NDF比为1.40的基础饲粮，SARA组依次饲喂NFC/NDF比为1.40、1.79、2.31和3.23四种饲粮诱导试验动物发生SARA。SARA诱导成功后从SARA组中随机选取4只患病动物让其自由采食混合粗饲料4周使其恢复，即post-SARA组。采用pH值监测系统连续监测瘤胃pH值以判定SARA的严重程度。采集瘤胃腹囊上皮组织，利用透射电镜、尤斯灌流室、PCR和Western blot等先进技术检测瘤胃上皮的形态结构和功能。结果表明：与对照组相比，（1）SARA组瘤胃上皮乳头长度、宽度、表面积和角质层厚度显著增加(P<0.05)，棘基层厚度和上皮总厚度则显著降低(P<0.05)。post-SARA组这些参数则趋向于恢复到对照组水平(P>0.05)。同时透射电镜结果显示，SARA减少了瘤胃上皮紧密连接数量，加宽了上皮细胞之间的间隙。（2）SARA组和post-SARA组瘤胃上皮短路电流（Isc）、组织导电性（Gt）以及辣根过物氧化酶（HRP）通过瘤胃上皮的流速均显著增加(P<0.05)，这表明SARA可引起瘤胃上皮通透性持续升高，进而导致其屏障功能长期受损。（3）SARA组和post-SARA组瘤胃上皮紧密连接蛋白CLDN1, OCLN and ZO-1的mRNA和蛋白表达量均极显著下调(P<0.01)。由此可见，SARA可导致瘤胃上皮屏障结构和功能持续受损，这与瘤胃上皮紧密连接蛋白表达下调密切相关，而且瘤胃上皮屏障功能的恢复滞后于形态结构的恢复。

Grain-induced subacute ruminal acidosis (SARA) impairs rumen epithelial barrier function, but it is yet to be determined if SARA can cause persistent damage to the morphology and function of the rumen epithelial barrier.  The objective of the present study was to investigate if SARA has persistent effects on the morphological structure and permeability of ruminal epithelium and the expression of the genes involved in epithelial barrier function using a lactating goat model.  Twelve mid-lactating Saanen goats with rumen cannulas were randomly assigned to 1 of 2 groups: control group (Ctrl, n=4) fed a basal diet with a non-fiber carbohydrate (NFC) to neutral detergent fiber (NDF) ratio of 1.40, and SARA group (SARA, n=8) fed the same basal diet but with increasing NFC to NDF ratio from 1.4 to 1.79, 2.31, and 3.23 overtime to induce SARA.  At the end of the SARA challenge (post-SARA), 4 goats were randomly selected from the SARA group and fed only hay mixture ad libitum for another 4 weeks to allow for restitution (post-SARA).  Ruminal pH was continuously recorded to monitor the severity of SARA.  Samples of the ventral ruminal epithelium were collected after slaughter to examine the structural and functional changes of the ruminal epithelium using transmission electron microscopy (TEM), Ussing chambers, qRT-PCR, and Western bolt analyses.  Compared with the Ctrl group, ruminal papilla length, width, surface area and thickness of stratum corneum increased (P<0.05), while stratum spinosum and basale thickness, and total depth of the epithelium decreased (P<0.05) in the SARA group.  These changes diminished or tended to return to the levels of the Ctrl group in the post-SARA group (P>0.05).  The SARA challenge also decreased cellular junction and widened the intercellular space between epithelial cells.  Rumen transepithelial short-circuit current (Isc), tissue conductance (Gt), and mucosa-to-serosa flux of paracellular horseradish peroxidase (HRP) all increased (P<0.05) both in the SARA and post-SARA groups, which indicates that SARA can induce a sustained increase in epithelial permeability and barrier dysfunction.  Moreover, the mRNA and protein expressions of CLDN1, OCLN and ZO-1 were down-regulated (P<0.01) in both the SARA and post-SARA groups.  The results of this study showed that SARA could result in sustained epithelial barrier dysfunction, at both structural and functional levels, which is associated with decreased expression of rumen epithelial tight junction proteins, and the restitution of rumen epithelial barrier function is slower than that of its morphology.