Institute of Veterinary Physiology, Faculty of Veterinary Medicine, Leipzig University, Leipzig, Germany.
J Dairy Res. 2020 Aug;87(3):322-329. doi: 10.1017/S0022029920000369. Epub 2020 May 20.
The reticulorumen, as the main fermentation site of ruminants, delivers energy in the form of short-chain fatty acids (SCFA) for both the animal as well as the ruminal wall. By absorbing these SCFA, the ruminal epithelium plays a major role in the maintenance of intraruminal and intraepithelial acid-base homoeostasis as well as the balance of osmolarity. It takes up SCFA via several pathways which additionally lead to either a reduction of protons in the ruminal lumen or the secretion of bicarbonate, ultimately buffering the ruminal content effectively. Nutrition of the epithelium itself is achieved by catabolism of the SCFA, especially butyrate. Catabolism of SCFA also helps to maintain a concentration gradient across the epithelium to ensure efficient SCFA uptake and stability of the epithelial osmolarity. Furthermore, the ruminal epithelium forms a tight barrier against pathogens, endotoxins or biogenic amines, which may emerge from ruminal microorganisms and feed. Under physiological conditions, it reduces toxin uptake to a minimum. Moreover, the epithelium seems to have the ability to degrade biogenic amines like histamine. Nonetheless, in high performance production animals like dairy cattle, the reticulorumen is confronted with large amounts of rapidly fermentable carbohydrates. This may push the epithelium to its limits, even though it possesses a great capacity to adapt to varying feeding conditions. If the epithelial limit is exceeded, increasing amounts of SCFA lead to an acidotic imbalance that provokes epithelial damage and thereby elevates the entrance of pathogens and other potentially harmful substances into the animal's body. Hence, the ruminal epithelium lays the foundation for the animal's health, and in order to ensure longevity and high performance of ruminant farm animals, it should never be overburdened.
反刍动物的瘤胃是主要的发酵部位，以短链脂肪酸 (SCFA) 的形式为动物和瘤胃壁提供能量。通过吸收这些 SCFA，瘤胃上皮在维持瘤胃内和上皮内酸碱平衡以及渗透压平衡方面发挥着重要作用。它通过几种途径吸收 SCFA，这些途径除了导致瘤胃液中质子减少外，还会导致碳酸氢盐的分泌，最终有效地缓冲瘤胃内容物。上皮本身的营养是通过 SCFA 的分解代谢来实现的，特别是丁酸。SCFA 的分解代谢还有助于维持跨上皮的浓度梯度，以确保有效的 SCFA 吸收和上皮渗透压的稳定。此外，瘤胃上皮形成了一道针对病原体、内毒素或生物胺的紧密屏障，这些物质可能来自瘤胃微生物和饲料。在生理条件下，它将毒素吸收降至最低。此外，上皮似乎有能力降解生物胺，如组胺。尽管如此，在高产奶牛等高性能生产动物中，瘤胃会面临大量快速可发酵的碳水化合物。这可能会使上皮达到极限，尽管它具有适应不同饲养条件的巨大能力。如果上皮的极限被超过，越来越多的 SCFA 会导致酸中毒失衡，从而引发上皮损伤，并增加病原体和其他潜在有害物质进入动物体内的风险。因此，瘤胃上皮为动物的健康奠定了基础，为了确保反刍动物农场动物的长寿和高性能，绝不应该过度负担。
