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

Lead Research Organisation: University of Strathclyde
Department Name: Electronic and Electrical Engineering

Abstract

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.

Technical Summary

Sub-acute ruminal acidosis (SARA) affects some cattle herds, but not others, and individual animals within herds, but not others. The root cause of the dysfunction is the loss of control of ruminal and possibly intestinal pH. SARA is generally caused by grain feeding, but the basis of the variability requires better definition and the precise cause of inflammation and pathology remains uncertain. This project will monitor six beef and two dairy herds for nutrition and management and relate the information to post-mortem scores of ruminal wall lesions, liver abscesses and laminitis. The potential value of remote motion sensors in alerting farmers to problematic animals will be explored. Ruminal digesta and ruminal epithelial tissue samples taken post mortem will be analyzed by state-of-the-art microbiomic analysis based on 16S rRNA gene sequences, in order to identify significant differences in microbial communities in different animal types. Different Escherichia coli biotypes will be monitored. Bacteria will be isolated from least affected animals for their ability to inhibit the growth or adhesion properties of E. coli, on the basis that these animals may already possess bacteria that protect them from SARA. Candidate strains will be evaluated for their potential usefulness as probiotics to prevent or treat SARA. The hypothesis that soluble lipopolysaccharide (LPS) lies at the heart of the inflammation which results in pathology will be tested by measuring the quantities and nature of cell-free LPS in different animals. Possible feed additives that adsorb or break down LPS will be evaluated in digesta samples from badly affected animals. Demonstration animal trials will be carried out in the third year of the project to test the potential nutritional, management and feed-additive solutions identified by the project's results.

Planned Impact

A wide international spectrum of academic researchers will benefit from the project, because SARA is a widespread problem internationally. Researchers interested in ruminant health and welfare and those whose main interest is ruminant gut microbiology will be the primary beneficiaries. They will be able to translate the results to their own production conditions where SARA is endemic. The results will be of wider interest, however, because although SARA is a disorder that afflicts ruminant species, researchers interested more generally in inflammation that originates in the gastrointestinal tract of other species, including man, will benefit. Related fields include equine health and poultry production: researchers in these areas will build upon the novelty of this project to determine if the aetiology of their target diseases, in terms of microbiology, inflammatory factors and pathology compare. New research and research proposals for these different animal species could result. Medical researchers may benefit too: the concept of soluble LPS has not yet been explored in human disease, for example. One might speculate that soluble LPS may have an important, as yet uninvestigated, role in inflammatory bowel disease (IBD) in man. Our project may spark useful medical research in this area. Microbiome profiling will provide information about how diet and the individual animal affect numbers and species of methanogenic archaea in the rumen, thereby aiding research into greenhouse gas emissions from animal agriculture. Ruminal microbial ecology in UK ruminants is under-studied in the modern era: the project will help correct that deficiency.
Veterinary practitioners and public sector advisers from colleges of agriculture and levy bodies will benefit by being better equipped to advise farmers. The project will describe management and nutritional factors associated with variations in the incidence of SARA, information that farmers' advisers can use on-farm. Vets will be able to make better diagnosis of SARA and they will be able to suggest solutions from those feed additives coming out of the SARA project. The probiotic(s) will be useful to help prevent pathological problems in susceptible farms and animals. The adsorbants may be useful in prevention but also to treat the condition. The market potential for a successful feed additive is many millions of pounds. The advisors may consider the remote monitoring system a useful mechanism to monitor the success or otherwise of strategies to ameliorate SARA. The academic partner expert in remote broadband technology has a spin-out SME that will benefit if the technology is found to be generally useful in an on-farm situation. The companies selling these additives and devices will benefit commercially. Initially, those will be from within the consortium. However, as the results are disseminated, more companies in the UK and worldwide will take up the technologies.
Farmers will benefit economically. The beef industry nationwide has a value of £2.22bn at 2009 values. It follows that even a 5% overall loss of productivity caused by SARA may cost livestock producers £111M p.a. Dairying has a similar incidence of therefore the loss to farmers (and the UK economy) could easily exceed £200M p.a. The economic impact will be felt across the globe in countries that suffer from SARA in their ruminants, including the US (26% of mid-lactation cows suffer SARA), the Netherlands and Germany (18%). Livestock production in the UK will gain against its international competitors and, by retaining the IP in the UK, the economic competitiveness of the United Kingdom will be enhanced. Societal benefit will stem from improved economics and sustainability of food production and a healthier national herd. The livestock will benefit by being less subject to the distress of SARA, thus enhancing animal welfare.
 
Description Key Results (Task 3)
The main ingredient of all the diets on the six farms was barley, which was grown and processed on each of the farms. The diets were diverse, despite being barley-based. Sugar beet pulp, soya hulls and a buffer against acidosis were only used on one farm each and yeast was used on all farms. Rumitech was included only on two of the high concentrate, high risk farms.

The farm of origin was the dominant effect on the measured variables, almost all variables differing significantly among farms. The animals on the high risk diets had lower concentrations of short-chain fatty acids (SCFAs) and higher concentrations of lactate and LPS in the reticuloruminal fluid. The diameters of the strata granulosum, corneum and of the vasculature of the papillae were increased on the high-risk farms, as was the expression of the gene TLR4 in the ruminal epithelium, while the expression of IFN-? and IL-1ß was lower, as were the counts of CD3+ and MHCII+ cells. As the proportion of barley in the ration increased, so did the concentration of reticuloruminal and caecal lactate, reticuloruminal histamine, LPS and the thickness of the strata corneum and granulosum, while there was a reduction in the total SCFA concentration in the reticulorumen the expression of IFN-? and count of MHCII+ cells in the ruminal epithelium. Increasing the proportion of fines in the ration had mostly similar effects to increasing the proportion of barley, but in several cases, the effect was stronger and there was also an increase in the expression of NHE3 gene in ruminal epithelium. Despite variation among farms, there were few strong associations of gene expression variables with the other input or dependent variables. NHE3 expression was positively associated with the concentration of LPS in reticuloruminal fluid (r = 0.30, p < 0.05), and with the level of fines in the ration. IFN-? expression decreased as barley and fines in the ration increased. The levels of expression of the genes in the epithelium correlated moderately or highly with each other. They were not strongly correlated with the thickness of the stratum granulosum, nor with the density of CD3+ nor MHCII+ cells, nor lactate concentration in reticuloruminal or caecal fluid.

A surprising result from this study was the lack of obvious pathology in the rumens that were examined. We used a gross scoring system with 5 categories but only 15 of 119 animals in total scored anything other than a baseline normal score ("A") for the variable "Pre-Score". We therefore combined the non-"A" categories for analysis and there was no strong relationship between the pre score of the ruminal mucosa with any of the factors considered in the study. This should not be taken as definitive evidence that there was no pathology in the rumens that we examined, but that none was detected using our matrix. The lack of clear-cut histological signs of pathology was consistent with this observation. As a consequence of the lack of any distinct pathology, one of the objectives of the study, to characterise the possible pathological features of the reticulorumen in cattle from divergently managed intensive beef finishing farms with high rates of concentrate feeding, was not able to be achieved. Nonetheless, elevated concentrations of LPS and lactate were seen in the reticulorumens of cattle on diets with high percentages of barley and fines. Of the dependent variables measured in this study, LPS and lactate concentrations are the best indicators of pathology, however without any independent marker for performance or health (eg daily live weight gain, feed intake, clear evidence of systemic illness) it was not possible to determine de novo thresholds at which LPS or lactate concentrations indicate pathology. A previously proposed threshold of mmol/l of lactate above which an animal is considered to be suffering from acute acidosis seems reasonable and would have been exceeded by 4% of the animals in this study.
Key Results (Task 4 and Task 6)
The microbial population of the rumen was found to be typical of an animal consuming a high starch diet. The population in the caecum was significantly different to that of the rumen and was less diverse. Furthermore, the microbial population in both the rumen and caecum seemed to be unique to individual farms. Previous research has shown that E. coli, which is a proteobacteria, is a potential driver of the inflammation associated with SARA. Surprisingly, there were negligible counts of E. coli in the rumen and caecum, and Proteobacteria in the caecum appeared to drastically reduce. Furthermore, the predominant proteobacteria species in the caecum actually belonged to the Moraxellaceae. This clade had not previously been characterised in the ruminant; however, previous research shows that it can have inflammatory properties. In addition, Moraxellaceae were more common in the caecum in animals who consumed feed that contained a high proportion of "dusty" feed (i.e. TMR <1.18 mm). There was also a relationship between the "dusty" feed and apparent inflammation of the rumen wall. The role of caecal Moraxellaceae and dusty feed on the caecum warrants further investigation.
Farmer Facing Messages
It is interesting that "dusty" feed appears to have a relationship with rumen inflammation and the presence of Moraxellaceae in the caecum. The negative effects of SARA could be reduced by changing physical treatment of the barley grain to avoid dust, and possibly clearing out dusty feed from the bottom of the food trough.

Further Exploitation by Industry
Industry will need to be aware of any subsequent effects on the caecum. Even if the rumen appears healthy, the caecum is less well adapted to cope. The study also highlights that E. coli may not be the only culprit and that other bacterial species may have an influence on the inflammation associated with SARA.
Exploitation Route Messages and industry exploitation
• When challenged with high starch and low NDF diets, an inflammatory condition (SARA) can develop in cows before there are signs of reduced milk fat or reduced milk production.
• Direct fed microbials, particularly Probios Complete and an Enterococus faecium strain used alone, increased reticuloruminal pH.
• Traditional methods of diagnosing SARA on the basis of reticuloruminal pH are likely to be too stringent and will not correctly identify some farms on which SARA is contributing to disease.
• Previously reported associations of dietary challenge using high concentrations of soluble carbohydrates with lipopolysaccharide and histamine concentrations in the reticuloruminal fluid were confirmed.
• Previously reported associations of dietary challenge using high concentrations of soluble carbohydrates with inflammatory markers in the blood were confirmed.
• One or more of the associated blood or reticuloruminal fluid variables might be developed as a potential bio-markers for the early identification of diets that contain excessive soluble carbohydrate relative to effective fibre.
Sectors Agriculture, Food and Drink

 
Description Messages and industry exploitation (Task 3) There are three main messages from this study; Firstly, despite a reasonable expectation of some degree of equivalence among farms due to their similar location, management and broad nutritional inputs, farm to farm variation in rations and practices was wide and the effects of individual farm factors on animal physiology dominated any other factors that were measured. Some of the potential confounding factors at the level of the farm include specific nutritional components, mixing and feeding practices, stocking density, faecal or bedding management, the source of cattle, variation in their genotype and enteric microbiome, health and nutritional management before arrival at the farm of origin. This observation has implications for the design and interpretation of future studies on the impact of interventions in the field, in which a higher level of replication is required than is required for conventional, controlled experimental studies. It also implies a need to consider the effects of any nutritional intervention as part of a complex, interactive network of input factors. Secondly, the study provides an insight into the adaptive capacity of cattle. The animals in this study were those that made it to slaughter with the rest of their cohort and over the three months or so that they were on feed they had all successfully adapted to a highly challenging diet with little or no evidence of pathology, despite the fact that 4% of them had reticuloruminal lactate concentrations that were consistent with acute acidosis. Future studies on the effects of high levels of soluble carbohydrate supplementation or seeking to describe pathology associated with SARA would be more effective if they were to focus on the animals that failed to meet performance targets. The third message from the study is that the proportion of fines in concentrate-based total-mixed rations is a strong driver of the reticuloruminal SCFA, lactate and histamine concentrations. It follows that as much care is required with presentation of the concentrate diet as with its formulation. An understanding that rumination signatures can be detected using collar technology has inspired organisations such as Harbro to examine how this signature can be translated into information relevant to the farming community
First Year Of Impact 2014
Sector Agriculture, Food and Drink
Impact Types Economic

 
Title Sub Acute Rumen Acidosis (SARA): a study relating rumen pH value and low activity. 
Description "This archive contains collar based accelerometer data that was used to identify changes in animal behaviour associated with the onset of SARA as determined by a drop in rumen pH value measured using a rumen pH bolus. The measurements were made on cattle at Cochno farm Oct to Dec 2015. These are associated with rumen pH measurements. Where there are strong rumination pH changes, these can often be associated higher incidences of low activity. This is currently being analysed. The experiments took place between Oct-Dec 201. Additional data is provided running to March 2016." 
Type Of Material Database/Collection of data 
Provided To Others? No  
Impact Not Applicable 
 
Description Joint research with SRUC, Scotland's Rural College 
Organisation Scotland's Rural College
Department Animal and Veterinary Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Joint research
Collaborator Contribution Joint research
Impact Joint research and collaboration
Start Year 2012
 
Description Joint research with University of Aberdeen 
Organisation University of Aberdeen
Country United Kingdom 
Sector Academic/University 
PI Contribution University of Strathclyde researchers worked on this project with researchers from University of Aberdeen
Start Year 2012
 
Description University of Kentucky 
Organisation University of Kentucky
Department Department of Animal and Food Sciences
Country United States 
Sector Academic/University 
PI Contribution Research into animal welfare on Kentucky farm
Collaborator Contribution Data Analysis, animal monitoring
Impact research
Start Year 2015
 
Description Advances in monitoring of livestock 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact Plenary talk at European Association of Animal Science, Warsaw August 2015. Contributors - Dave Ross, Craig Michie, Carol-Anne Duthie, Shane Troy, Ivan Andonovic. Presentation delivered by D Ross
Year(s) Of Engagement Activity 2015