The differences between a healthy/unhealthy biome - gastrointestinal disease - disturbances of the gut bacteria
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By Carol Hughes
Gastrointestinal diseases and upsets are common in thoroughbred racehorses, causing discomfort, loss of performance and even mortality. Every common gastrointestinal disease can be linked back to disturbances (dysbiosis) of the gut bacteria. Currently, new gene technology is driving research at an intense rate, providing new insights into the equine microbial community (1) and providing both trainer and the vet with a powerful and accurate analytical tool to improve health and manage disease.
The gastrointestinal tract of the horse is colonized by trillions of microorganisms, which includes 1,000-1,500 different species, making up around 95% of the biome; the other 5% are made up of archaea, protozoa, fungi and viruses. Though most studies concentrate on identifying species of bacteria and linking to health and disease. Other members of the biome have equally important roles to play. In the racehorse, a major player is the Enterobacteria phage PhiX174, which is a bacterial virus that protects the horse against E-coli (2).
The microbial community has co-evolved with the host, performing essential and vital activities such as the extraction of energy and nutrients from foodstuff, synthesis of vitamins, interaction with the immune system and cross talk with the brain, which is thought to affect temperament and behaviour. Taxonomic and functional compositions of the gut microbiome are rapidly becoming viable indicators of horse health and disease.
Each member of the microbial community has a different but synergistic role, which is beneficial to the health of the horse; e.g., the fungi break down the indigestible parts of forage plants, such as the polysaccharides, whilst the ciliate protozoa contribute to the process by producing a wide range of enzymes that the horse is unable to make, impacting and benefitting the immune system. Microbial fermentation of cellulose, hemicellulose and lignin reduces the structural and non-structural plant wall material into carbohydrates, proteins (amino acids) and lipids, and produces volatile and short chain fatty acids (2a), which are the primary source of energy for the horse. The bacteria contribute the most to the degradation of ingested food, producing the final components of the fermentation process, which are acetic, propionic and butyric acid, methane and carbon dioxide.
The gastrointestinal tract of the horse is sensitive to change, stress, environment and medication, which cause imbalances or dysbiosis (3). Establishing or profiling a healthy baseline in the horse is difficult as variations exist between individuals, breeds, diets and locations; the thoroughbred racehorse is a very different animal to the Shetland pony or an Irish Draught. Fitness training alters the microbiome further; for these reasons it is important to study the thoroughbred as a population separate from other breeds and to analyse, where possible, racehorses training in a similar environment and location.
With this in mind, since 2017 there has been an ongoing project to study and profile the microbial populations of over 1,000 racehorses based in Newmarket, throughout the racing season; and the data produced has been used to develop profiles of the differences between a healthy/unhealthy biome. The project utilizes the cutting-edge Illumina MiSeq technology, which is the most accurate and up-to-date, preferred by genomic researchers around the world.
The Biome In Health
Elite racehorses have higher levels of a super-phylum bacteria
Questions asked….
Elite racehorses are trained to achieve peak fitness, but is it possible that they can gain an extra edge from the input of the hind gut bacteria?
How different is the microbiome of a Group 1 horse, and is it possible to identify the bacteria responsible for the extra edge?
Answers found….
Human scientists have known for some time that the microbiome of an elite human athlete is different (4), with faster metabolic pathways (amino acids and carbohydrates) and higher levels of faecal metabolites (microbial-produced short-chain fatty acids) acetate, propionate and butyrate associated with enhanced muscle fitness. The human and elite equine athlete do share similar microbial profiles, having higher percentages of the bacteria that manufacture short-chain fatty acids and higher levels of the super-phylum verrucomicrobia; these increase as the season/training progresses.
Image of the analysis of the microbiome of a Group 1 horse, compared to a non- group horse.
What is known about this super-phylum?
It has two main members: Methylacidiphilaceae and Akkermansia
Verrucomicrobia Methylacidiphilaceae thrive and proliferate on the ammonia produced from the degradation of starch and protein (5), whereas starch produces very high levels of ammonia. The bacteria make enzymes (ammonia monooxygenase) (6), which convert ammonia into nitric oxide (7). The nitric oxide has three major benefits to a racehorse:
Helps repair and renew the gut wall (8)
Enhances performance and increases exercise tolerance (9)
Improves vascular function and metabolism (10)
Verrucomicrobia Akkermansia is a mucus-eating specialist, living and thriving within the gut wall, digesting mucin from the mucosal lining (10a) with a unique ability to metabolise galactose and melibiose (11) for energy. Akkermansia in the human biome significantly increases the numbers of metabolic pathways. Horses with gastric ulcers have very low levels, perhaps indicating its function in both performance and disease.
Comparing percentages of the super-phylum amongst other breeds/locations/environments gave good insight into how important and relevant verrucomicrobia is to the racehorse.
Verrucomicrobia varied significantly from group to group; the lowest levels were found in the sedentary and/or companion animal group which was comprised of 250 horses (gently hacked or unridden companions). The Carneddau are an ancient herd of wild horses that graze freely in the mountains of Snowdonia, and the Pottokas are from Spain. The CCI-L group was made up of 10 horses eventing at International One Day Event Level.
The Non-Group horses were based in Newmarket and analysed at the height of the flat season in July, whilst the Group 1 horses started the season (Feb) with levels of 10%; these levels increased as the season continued until finally levelling out at 23% in July through to September when the testing finished.
Fig 3: The microbiome of Group 1 horses indicating higher diversity and stability.
Fig 4: Image of thoroughbreds in training diagnosed with EGGD.
Why the horses diagnosed with Equine Glandular Gastric Disease had lower levels of verrucomicrobia is unknown at this time, horses with EGGD had a completely different profile to the healthy Group 1 horses. See Fig 3 and 4. …
