The engine room of the horse: digestive anatomy and the microbiome

As a monogastric, hindgut fermenter, the horse relies on the caecum and colon as the main site of forage breakdown, energy conversion and nutrient supply.

These organs are home to trillions of microbes which breakdown the digesta via the process of fermentation and convert it into fuel such as volatile fatty acids, providing essential nutrients and energy to the rest of the body.

In fact, the microbiome within the hindgut of the horse, is intrinsically linked to the overall health and performance of the animal. Not only is the hindgut microbiome responsible for the fermentation of digesta, and in turn up to 70% of the horse’s energy requirements, but also for 80% of the immune function. Furthermore, it is also home to the majority of neuroreceptors via the gut–brain axis - a phenomenon that may be the future of ensuring optimal welfare of our equines.

Each horse has its own very unique microbiome, like an individual fingerprint. However, each horse has what is known as the ‘core microbiome’ and supporting this is a very clear and positive starting point when it comes to supporting optimal gut health.

Both beneficial and pathogenic microbes are present within the microbiome of the hindgut, and it is a question of balance that keeps the environment harmonious.

Many factors of management influence this balance. Some are within our control such as diet, starch intakes and feeding time scales but many are not and can still have a negative impact on the balance of the microbes. These include:

  • Transport
  • Competition
  • Illness
  • Time spent stabled
  • Change in rider

Let’s face it, when so many factors have a role to play it is hard to control them all and despite our best efforts, our horses are still exposed to an element of stress throughout the day. When the balance of microbes is negatively affected, hindgut dysbiosis occurs and conditions within the hindgut very quickly deteriorate. Beneficial microbes begin to die off and pathogenic microbes quickly increase in numbers to produce unwanted substances such as lactic acid.

Acidic conditions in the hindgut can lead to the death of gram negative bacteria which releases endotoxins, histamines, etc. The damage caused by these substances cause inflammation in the lining of the gut and a breakdown of the lining, causing 'leaky gut' - allowing the movement of microbes and toxins from the gut into the bloodstream contributing to issues such as laminitis. Acidic conditions in the gut also causes discomfort in the colon and can also lead to a horse favouring one side of its body, resulting in fatigue and increase risk of leg or joint injury.

Systemic acidosis can also proliferate and poor recovery, colonic ulcers, gastric ulcers - among other metabolic conditions - can occur when acidic conditions within the hindgut occur.

We can take steps to mitigate the effects of these stressors on the microbiome. Contact us today to find out more.