Institute of Animal Nutrition and Functional Plant Compounds, Department for Farm Animals and Veterinary Public Health, Vetmeduni Vienna, Veterinaerplatz 1, 1210 Vienna, Austria.
Institute for Organic Farming and Biodiversity, LFZ Raumberg-Gumpenstein, 4600 Wels, Austria.
J Dairy Sci. 2013 Apr;96(4):2293-2302. doi: 10.3168/jds.2012-6187. Epub 2013 Feb 10.
High-producing ruminants are commonly fed large amounts of concentrate to meet their high energy demands for rapid growth or high milk production. However, this feeding strategy can severely impair rumen functioning, leading to subacute ruminal acidosis. Subacute ruminal acidosis might have consequences for electrophysiological properties by changing the net ion transfer and permeability of ruminal epithelia, which may increase the uptake of toxic compounds generated in the rumen into the systemic circulation. The objective of the present study was to investigate the effects of excessive barley feeding on the electrophysiological and barrier functions of the ruminal epithelium and serum inflammation and ketogenesis markers after a long-term feeding challenge, using growing goats as a ruminant model. A feeding trial was carried out with growing goats allocated to 1 of the 3 groups (n=5-6 animals/group), with diets consisting exclusively of hay (control diet) or hay with 30 or 60% barley grain. Samples of the ventral ruminal epithelium were taken after euthanasia and instantly subjected to Ussing chamber experiments, where electrophysiological properties of the epithelium were measured in parallel with the permeability of marker molecules of different sizes [fluorescein 5(6)-isothiocyanate and horseradish peroxidase] from luminal to apical side. Additionally, ruminal fluid and blood samples were taken at the beginning of the experiment as well as shortly before euthanasia. Ruminal fluid samples were analyzed for volatile fatty acids and pH, whereas blood samples were analyzed for lipopolysaccharide, serum amyloid A, and β-hydroxybutyrate. Electrophysiological data indicated that barley feeding increased the epithelial short-circuit current compared with the control. Tissue conductance also increased with dietary barley inclusion. As shown with both marker molecules, permeability of ruminal epithelia increased with barley inclusion in the diet. Despite a lowered ruminal pH associated with increased volatile fatty acids (such as propionate and butyrate) concentrations as well as altered epithelial properties in response to high-grain feeding, no signs of inflammation became apparent, as blood serum amyloid A concentrations remained unaffected by diet. However, greater amounts of grain in the diet were associated with a quadratic increase in lipopolysaccharide concentration in the serum. Also, increasing the amounts of barley grain in the diet resulted in a tendency to quadratically augment serum concentrations of β-hydroxybutyrate and, hence, the alimentary ketogenesis. Further studies are needed to clarify the role of barley inclusion in the development of subacute ruminal acidosis in relation to ruminal epithelial damage and the translocation of toxic compounds in vivo.
高产反刍动物通常需要大量的精饲料来满足其快速生长或高牛奶产量的高能量需求。然而，这种饲养策略会严重损害瘤胃功能，导致亚急性瘤胃酸中毒。亚急性瘤胃酸中毒可能会通过改变瘤胃上皮的净离子转移和通透性而对电生理特性产生影响，这可能会增加瘤胃中产生的有毒化合物进入全身循环的吸收。本研究旨在使用生长山羊作为反刍动物模型，研究长期饲养挑战后过量大麦喂养对瘤胃上皮的电生理和屏障功能以及血清炎症和酮生成标志物的影响。用生长山羊进行饲养试验，将其分配到 3 个组中的 1 个（n=5-6 只/组），日粮由干草（对照日粮）或 30%或 60%大麦谷物组成。安乐死后立即采集腹侧瘤胃上皮样本，并立即进行 Ussing 室实验，同时测量上皮的电生理特性和不同大小标记分子（荧光素 5（6）-异硫氰酸酯和辣根过氧化物酶）从腔侧向顶侧的通透性。此外，在实验开始时以及安乐死前不久采集瘤胃液和血液样本。分析瘤胃液样品中的挥发性脂肪酸和 pH 值，分析血液样品中的脂多糖、血清淀粉样蛋白 A 和β-羟丁酸。电生理数据表明，与对照相比，大麦喂养增加了上皮短路电流。组织电导也随着日粮中大麦的加入而增加。正如两种标记分子所示，随着日粮中大麦含量的增加，瘤胃上皮的通透性增加。尽管高谷物喂养导致丙酸和丁酸等挥发性脂肪酸（VFA）浓度升高以及与上皮性质相关的改变，但由于血清淀粉样蛋白 A 浓度不受饮食影响，因此没有出现炎症迹象。然而，饮食中谷物含量增加与血清中脂多糖浓度呈二次增加相关。此外，日粮中大麦含量的增加导致血清β-羟丁酸浓度呈二次增加趋势，因此，食物中的酮生成增加。需要进一步的研究来阐明大麦的摄入在亚急性瘤胃酸中毒的发展中的作用，以及与瘤胃上皮损伤和有毒化合物在体内易位有关。
