Hind gut health is a phrase we hear a lot about at the moment, and it is an important issue. A healthy hind gut has so many positive effects on the horse, so it’s well worth understanding a bit about it.
In this blog vet Liam Gamble gives a basic overview of the importance of good hind gut health and the microbiome. Liam was one of our guest presenters at the Horses Inside Out Conference where he discussed this topic in lots more detail.
An introduction to the gastrointestinal microbiota
The GI tract is home to a complex ecosystem of microorganisms which is called the microbiota. In fact, it's not just the GI tract, which have microbiota, various different body systems have their own microbiota - the urinary tract as well the skin, even the surface of your eye, the cornea has a distinct microbiota. However, we tend to focus on the GI tract because it's the best understood at the moment and arguably the most important as well.
In your horse’s GI tract, and indeed your own, there's a dynamic mixture of bacteria, fungi, parasites, archaea, and viruses. Often, we concentrate on the bacteria but we shouldn't underestimate the importance of the anaerobic fungi – the fungi that don't like oxygen, they're super important in breaking down big chunks of fibre in the horse's hind gut, and really kicking off that process of fermentation.
There are microbes all the way down the GI tract, but it's the microbes in the hindgut - the cecum and colon that are really important for equine health. They are a temple to fermentation - like a brewer's fermenter where the fibre is broken down.
“Think about all these different microbes in two very broad categories, some health positive and others health negative - good guys and bad guys.”
What are the microbiota doing for your horse?
The microbiota help so many things, some more obvious than others..
Helping Digestion
The horse’s diet is rich in fibre, which is rich in cellulose, which the horse can't break down himself, so he recruits all these microbes to do the job for him and to ferment the fibre and break down the cellulose. The bugs breaking down the complex fibre produce short chain fatty acids, which the horse is then able to absorb into the bloodstream, where they provide safe calories, feed the gut lining, and they reduce inflammation.
That's not the only thing that microbes are doing. Horses aren’t great at digesting lots of starch and if we feed them too much, it spills out from the small intestine into the hind gut where it isn't wanted. The bacteria in the microbiota break it down and produce lactic acid which reduces the pH and makes the hindgut more acidic, which can cause inflammation.
The Immune System
The next important consideration is their interplay with the immune system - 70% of the body's immune cells are in the gut.
When the microbiota is in the right balance it modulates the immune response. It makes it more active in some areas, and it dampens it down in others.
Liam suggests thinking about the immune system like a hyperactive child. If you give that child the right toys, then it focuses energy on those toys, but if you don't have the right toys, potentially they will wonder around your house and knock all your ornaments off the shelves.
It’s the same with the immune system. If the microbiota is in the right balance, that's like giving the immune system toys it likes to play with, focusing its energy in the right way. If there’s an imbalanced microbiota, the immune system starts knocking all the items off the shelves - it might raise an immune response to a food particle and the result might be food allergies, or it might cause more inflammation in the gut lining, which isn't what we want.
“Think of these bugs as little chemical factories that are constantly breaking things down, producing metabolites, maybe producing hormones, chemical messengers, producing inflammatory markers. These things don't stay in the gut they are absorbed into the bloodstream and may affect other body systems, such as the immune system, and even the brain.”