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

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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.