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Hind Gut Health and the Thoroughbred Racehorse

Updated: Oct 16, 2023

Thoroughbred racehorse diets are often high in concentrates, and their lifestyles generally involve intense training and frequent travelling. These are all factors that may influence the microbiome and the general health of the horse. This blog article presents information relating to the health of the hind gut of the thoroughbred racehorse.

About The Thoroughbred Horse’s Hind Gut Health

The horse’s hind gut is full of bacteria and other microorganisms that produce three-quarters of the horse’s energy. A change of diet or environment can cause disruption and disturbance of the gut bacteria community. This can promote the growth of bacteria that produce acid, which damages the lining of the hind gut and causes ulceration. Changes can also increase the bacteria that cause inflammation (colitis), disrupting energy production, muscle fibre mass and a healthy immune system.

As thoroughbred racehorses will often travel: to race meetings, pre-trainers, sales, etc, they tend to experience more frequent changes to their diet and environment than leisure or companion horses. This increases the likelihood of hind gut issues, such as acidosis and colitis.


Acidosis reduces the percentage of bacteria associated with performance and health. Plus, there is an increase in the risk factors for colic. Horses with an acidic hind gut have poor coats, are over anxious and find weight gain difficult.


Horses with colitis (inflammation of the hind gut) have higher numbers of pathogenic bacteria - i.e. those that cause disease. They have higher numbers of bacteria that ferment carbohydrates and convert glucose.

How Common Are Both?

Acidosis is thought to affect 80% of horses being fed a diet of concentrates and hay. Meanwhile, colitis and hind gut ulcers are thought to affect 44-60% of horses. Symptoms include: girthiness, diarrhoea, flank sensitivity, discomfort when being ridden and cribbing.

The Analyses

The hind gut of the horse is difficult to access. Therefore, the best method to profile the health of the hind gut is to analyse a faecal sample. Using the latest gene technology and sequencing, it is easy then to calculate the energy output and health of the microbial population as well as its contribution to the performance of the horse.

Diet exerts the biggest effect on the health of the microbiome. Some diets promote and increase the production of bacteria that promote inflammation or are amylolytic. Amylolysis is the process of converting starch into sugar by the action of enzymes or acids.

Following the analysis, it is possible to alter the diet to rebalance and restore the hind gut.

The Gut - Performance Axis

The microbiome has multiple links to health through pathways that include respiration, temperament, muscle development and metabolism. Having enough bacteria to produce and promote health and fitness is important for success.


These results include a count of the number and richness of the microbial species. A higher score indicates better stability of the hind gut. Horses given long term medication such as antibiotics and non-steroidal anti-inflammatory drugs (NSAIDs) will have a lower diversity score.

Percentage of the microbiome containing bacteria that manufacture lactic acid:

  • Healthy: 30%

  • Above Average: 45%

  • High (acidosis): >45%

Percentage of bacteria associated with inflammation colitis/ulcers:

  • Healthy: 30%

  • Above Average: 45%

  • High (acidosis): >45%

Percentage of bacteria associated with performance:

  • Healthy: 10% total

  • Unhealthy: <10%

Bacteria associated with energy, muscle development, good immune function and respiration include eubacteria, ruminococcus and oscillibacter.

Equibiome Faecal Test for Racehorses

The Equibiome faecal test for racehorses is designed for horses with gastric ulcers, hind gut discomfort, poor performance and respiratory discomfort. Our full genome analysis of the microbiome detects bacteria that can cause disease and provides useful insights into the gastrointestinal health status of thoroughbred racehorses.

Test kits are simple to use, with full sample collection instructions included with each kit. Simply collect the required sample and send it back to us via post. Once the test results are back from the lab, we will produce a report to include nutritional and health status. We can then recommend formulated biome food(s) to target the immune system and energy production.

Order your Equibiome equine faecal test kit for racehorses today via our online shop.

Our products are not designed to diagnose, cure, treat or prevent any disease.

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