Sub-acute ruminal acidosis: an interdisciplinary approach to understand and prevent a multifactorial disease

反刍动物，包括牛、绵羊和山羊，依靠消化道中的微生物活性来消化它们消耗的草和其他草料。平衡、稳定的消化（发酵）对于良好的生长或产奶至关重要。大多数畜牧生产者要求的生产率高于仅靠饲料喂养所能维持的生产率，并在饮食中加入一些谷物以提高生产率。肠道微生物从谷物中的淀粉比从草料中的纤维素更快地产生酸，导致以谷物为食的动物普遍存在较低的pH值。这对微生物有不利影响，微生物需要接近中性的pH值才能发挥最佳作用。这种亚急性瘤胃酸中毒（SARA）是反刍动物生产中的一个主要经济和健康问题。患有SARA的动物生产力较低，并且它们遭受瘤胃壁坏死、肝脓肿和蹄叶炎。SARA通常很难被农民发现-它是“亚急性”的，只有在屠宰时才能很容易地被发现。SARA是一种研究不足的疾病，因此只有少数论文讨论了SARA的饮食和微生物原因及其潜在病理学，特别是关于大肠的作用。该项目旨在了解为什么SARA在一些农场而不是其他农场普遍存在，这是一个常识，但没有很好的记录。将在这些农场监测农场管理条件和营养，并将跟踪动物屠宰，届时将评估病理损伤的程度。将采集瘤胃液和瘤壁组织样品进行分析，并对组织坏死、溃疡和蹄叶炎进行评分。SARA也会影响某些动物，但不会影响牛群中的其他动物。将利用遥感技术从外部监测反刍活动等活动，以提醒畜牧业生产者注意有问题的动物。对这些动物也将进行尸检分析。SARA的根本原因在于肠道微生物学的改变。消化物样品将被用于描述易感和非易感动物瘤胃和肠道中存在的微生物，其想法是某些微生物物种可能在引起疾病方面特别重要，而其他微生物物种可能具有保护作用。将研究从非敏感动物中分离的候选“益生菌”细菌，以期将其开发为饲料添加剂。可溶性脂多糖（LPS）在炎症中的作用将被研究。当细菌溶解时，LPS被释放出来-在人类医学中被称为“内毒素”。可以结合可溶性LPS以预防炎症的材料也将被研究作为潜在的饲料添加剂。总体目标是解释SARA发病机制的潜在机制，研究微生物组分析是否可以预测SARA的严重程度，并开发简单，非侵入性的方法来监测与SARA相关的动物行为并预防疾病。三个学术合作伙伴，三个互补的公司，苏格兰优质肉类和DairyCo参与了该项目。工业合作伙伴将确保在整个项目中保持与畜牧业的相关性，并确保产生影响的途径短暂而迅速。

Ruminant animals, including cattle, sheep and goats, rely on microbial activity in their digestive tract to digest grass and other forages that they consume. A balanced, stable digestion (fermentation) is essential for good growth or milk production. Most livestock producers require productivity higher than that which can be sustained by forage feeding alone, and include some grain in the diet to increase production rates. Gut microbes produce acids more rapidly from the starch in grain than the cellulose in forages, leading to lower pH values prevailing in grain-fed animals. This has adverse effects on the microbes, which require near-neutral pH to perform optimally. This sub-acute ruminal acidosis (SARA) is a major economic and health issue in ruminant livestock production. Animals suffering SARA are less productive, and they suffer from necrosis of the rumen wall, liver abscesses and laminitis. SARA is often difficult for the farmer to detect - it is 'sub-acute' and can only be detected easily at slaughter. SARA is an under-researched condition, such that only a small number of papers have addressed the dietary and microbiological causes of SARA and its underlying pathology, particularly concerning the role of the large intestine. This project aims to understand why SARA is prevalent on some farms but not others, an observation that is common knowledge but not well documented. Farm management conditions and nutrition will be monitored in these farms, and the animals will be followed to slaughter, when the extent of pathological damage will be assessed. Samples of ruminal digesta and wall tissue will be taken for analysis and tissue necrosis, abscesses and laminitis will be scored. SARA also affects some animals but not others within a herd. Remote motion-sensing technology will be used to externally monitor movements, such as rumination activity, that may alert livestock producers to problematic animals. Post mortem analysis will also be carried out on these animals.The root cause of SARA lies in altered gut microbiology. Digesta samples will be taken forward to describe the microbes that are present in the rumen and intestine in susceptible and non-susceptible animals, with the idea that some microbial species may be particularly important in causing the disease while others may be protective. Candidate 'probiotic' bacteria isolated from non-susceptible animals will be investigated with a view to developing them as feed additives. The role of soluble lipopolysaccharide (LPS) in the inflammation will be investigated. LPS is released when bacteria lyse - it is known as 'endotoxin' in human medicine. Materials that may bind soluble LPS to prevent inflammation will also be investigated as potential feed additives.The overall aims are to explain the underlying mechanism of pathogenesis of SARA, to investigate if microbiome analysis can predict the severity of SARA, and to develop simple, non-invasive methods for monitoring animal behaviour relating to SARA and preventing the condition. Three academic partners, three complementary companies, Quality Meat Scotland and DairyCo are involved in the project. The industrial partners will ensure that relevance to the livestock industry is maintained throughout the project and that the pathway to impact will be short and rapid.