Horse digestive system: equine gut health
The gut health of our equines plays a significant role in determining how healthy or unhealthy our horses will be. The equine digestive tract is a large and relatively complex system. Your horse’s health depends on how well you look after this digestive system and importantly, how well the microbial population within it remains “balanced”.
We are really only just beginning to understand how important your horse’s digestive health is to their overall health and wellbeing. But we know that it is so important! So if there is one area of equine nutrition you should devote your time to in order to improve your horse’s overall health, it is this one!
The following article gives you an introduction to equine gut health. It looks at the structure and function of the gut and the digestive process, how the way we feed horses impacts on the equine digestive system and its microbial population, and briefly covers some of the diseases and disorders that can occur when we feed in a way that doesn’t support digestive health.
Understanding how horses digest food
Your horse’s digestive system is comprised primarily of the stomach and small intestine, cecum and colon.
The digestive tract’s most important function is breaking down food. The equine digestive process occurs in every section of the horse’s gut. The digestive process is simply “big things being broken down into small things”. Once nutrients are broken down into small enough parts, they can be absorbed into the bloodstream.
Digestion and absorption occurs the entire length of the animal’s digestive system. But the way it happens in each section is different.
The stomach
The stomach’s primary role is to hold food and then pass it slowly to the small intestine where it will be at least partially digested. The start of the digestive process does, however, occur in the stomach.
In the stomach, the horse uses hydrochloric acid and digestive enzymes to prepare minerals for absorption and begin the protein digestion process. Stomach acid is required to activate the digestive enzymes. There is also a resident population of bacteria here and some microbial fermentation does take place. As far as we know, the stomach does not absorb nutrients.
The small intestine
The small intestine digests and absorbs fats, protein, sugars, and starch. Digestive enzymes (which are like small scissors whose job is to cut up food) as well as bile from the liver cut these nutrients into small pieces so that they can be absorbed into the bloodstream.
The rate of passage through the small intestine is quite fast. It speeds up if you feed your horse large meals, as the stomach then loses its ability to slowly release food to the small intestine. When rate of passage is too fast, nutrient absorption is reduced as the small intestine doesn’t have time to do its work.
The hindgut
The cecum and colon (made up of the dorsal colon and ventral colon) are collectively known as the hindgut. The hindgut is the centre for structural carbohydrate digestion. Structural carbohydrates, also known commonly as fibre, are digested in a process of microbial digestion. The hindgut is, in essence, a large fermentation vat. Your horse’s resident population of “good” fibre fermenting bacteria ferment the fibre from your horse’s feed to produce volatile fatty acids (VFAs). Your horse then absorbs these VFAs and uses them as a source of energy (calories).
The good bacteria in your horse’s cecum and colon play many roles in maintaining equine health. Plus the hindgut is also responsible for water and electrolyte absorption, which needs to be working properly to allow your horse to form normal fecal balls.
How is this related to equine health?
It is related in EVERY way! If you mess up your horse’s digestion, you really mess up your horse’s health. Colic in horses is the number one killer of horses worldwide. More than 90% of horses in some disciplines have gastric ulcers. My own studies found that almost 30% of horses in race training had hindgut acidosis, which is a severe imbalance of the bacteria in the cecum and colon.
As riders we also all struggle at some level with our horse’s behaviour. Science is starting to show us how shifts in gut microbial populations is tightly linked to behaviour.
All of these conditions affect the health and wellbeing of your horse plus the health of the gut microbes also affects immune function, hormone production, lung health, appetite, weight, hoof health, performance and ability to digest fibre.
It is so important that we understand that the way we feed horses has a huge impact on the risk of these diseases and disorders. The most effective way of reducing the risk is by understanding the horse digestive process, and by feeding in a way that supports digestive health, rather than destroying it.
How does what and how we feed affect gut health?
When we feed our horses we need to take into account what the horse’s nutrient requirements are so that the feeds provided actually give your horse what they need.
BUT, equally important is to consider how what you choose to feed will affect your horse’s digestive process, microbial population, and overall gut health.
Here are some of the ways what and how you feed can affect your horse’s digestive health:
Long periods of time without feed – if you are feeding your horse in meals, and there are long periods (more than four hours) where they go without something to eat, their stomach will empty and strong hydrochloric acid will start to accumulate. With an empty, highly acidic stomach, your horse is at increased risk of gastric ulceration.
Too much starch – starch is the main component of cereal grains. Research has shown that if you feed too much starch per meal or per day, the risk of gastric ulcers is increased.
Indigestible starch – if you feed cereal grains that have not been cooked prior to feeding, the starch is very difficult for a horse to digest in the small intestine. This means a majority of the starch from these ingredients will end up in the hindgut and can cause hindgut acidosis and microbial dysbiosis.
Not enough fibre – If you are not feeding your horse enough fibre, the good, fibre fermenting bacteria in the hindgut won’t have enough food to maintain a healthy microbial population. With fewer fibre fermenting bacteria, your horse can suffer from vitamin deficiency, loss of appetite, loss of immune function, leaky gut, inflammation, weight loss, diarrhea, poor hoof quality (increasing their need for specialized hoof care) and changes in behaviour. Low fibre diets are also a major cause of colic in horses. Low fibre intake also reduces saliva production which can increase the risk of gastric ulcers and they reduce the amount of time horses are eating and chewing which affects their mental health.
Top five tips for feeding to promote digestive health
Feeding in a way that properly supports the equine digestive process is not difficult. Here are the top five things you can do to keep your horse’s gut as healthy as possible:
Tip 1 – Feed lots of long stem fibre
Long stem fibre, in the form of forages like pasture, hay, or haylage will encourage a lot of chewing and salivation, which will support the health of your horse’s stomach (reducing the risk of gastric ulcers). As long stem forages takes longer for your horse to eat, they maximize the amount of time your horse will spend eating. This again reduces the risk of gastric ulcers.
The fibre will also feed the microbial populations of good bacteria in the hindgut to keep them healthy, and it will keep the hindgut full, reducing the risk of colic in horses.
Tip 2 – Feed in small meals
The rate of passage through a horse’s digestive tract is naturally quite fast. BUT, horses are trickle feeders. So they eat small amounts of feed, consistently over a 24-hour period. This means even though feed is moving relatively quickly, there are only small amounts of it passing through the small intestine at any one time to give it the best chance of digestion and absorption.
However, when we feed horses in large meals, twice per day, we suddenly create a situation where large amounts of feed are moving quickly through the small intestine. When this happens, less is digested and absorbed. So your horse becomes inefficient and needs to be fed larger amounts of feed to maintain weight. AND with components of the feed like starch ending up in the hindgut, gut health and microbial populations are also compromised.
The solution here is to feed in many small meals throughout a day. As a rule of thumb, horses should have constant access to forage. Any “hard feed”, particularly high starch feeds (>20% starch), should ideally be fed at no more than 200 grams per 100 kg BW (0.2 lb per 100 lb bodyweight) per meal. Your horse’s feed label may specify starch content. If you are unsure you can contact the manufacturer.
Tip 3 – Minimise starch
Feeding too much starch puts your horse at increased risk of gastric ulcers and hindgut acidosis. Plus high starch diets tend to be lower in fiber and may compromise the health and balance of bacteria in the hindgut.
My rule is if you can achieve calorie intake with fibre alone (i.e. hay, haylage, chaff, pasture and high energy fibres like beet pulp) you should do so. Grains should only be used where the horse can’t physically eat enough fibre to meet calorie requirements (as is sometimes the case if your horse is a broodmare or performance horse). Or where the horse has a large requirement for muscle glycogen to compete (which often only applies to racing thoroughbreds).
But remember, forage only will NOT be a complete diet. Always make sure you are meeting vitamin and mineral requirements by feeding a complete feed, balancer pellet or vitamin and mineral supplement. You can find your horse’s perfect diet using the My Happy Horse app.
Tip 4 – Feed cooked starch
If you are going to feed starch from cereal grains like wheat, barley, corn (maize), and rice or any by-product ingredients like rice bran and wheat midds (bran/pollard) that come from these grains, you should make sure the grains are well cooked prior to feeding. Grains and grain-based feeds that are extruded, micronized, steam flaked, steam pelleted or boiled will contain starch that can actually be digested in your horse’s small intestine.
Feeding cooked grains will maintain your horse’s digestive health by keeping starch out of the hindgut, preventing hindgut acidosis, and supporting the good fibre fermenting microbial population.
Tip 5 – Watch water intake
Water is an essential component of the equine digestive process. When your horse doesn’t drink enough, the contents of your horse’s gut can become too high in dry matter and they’re at risk of developing impaction colic.
Dirty, foul tasting water, cold water, hot water, water in a place where the horse doesn’t feel safe (e.g. the back of a stable) or unfamiliar water can all discourage your horse from drinking enough water.
To ensure your horse is drinking enough, keep the water clean (if you wouldn’t drink it yourself then it’s not clean enough), keep the temperature moderate where possible and be prepared when you are traveling to keep familiar sources of water with you or have a familiar way of flavouring the water to keep your horse drinking when he is not at home. If you are concerned your horse is not drinking enough water, add some salt to his feed and this will increase water intake.
Healthy gut, healthy horse
When feeding your horse, you must always consider the impact of what you are feeding and your feeding management on the digestive process. Such a huge part of equine health is determined by the health of the gut!