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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 his 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 it’s 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. For a detailed description of the horse’s gastrointestinal tract, please see https://feedxl.com/31-the-gastrointestinal-tract/

Horse GI Tract

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 into small things”. Once nutrients are broken down into small enough parts, they can be absorbed into the bloodstream.

The 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 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. For more detailed information on feeding for hindgut health please see https://feedxl.com/15-keeping-the-hindgut-healthy/

How is this related to equine health?

Well, 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. Our 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 they will cause problems like loss of appetite, weight loss, and poor hoof quality.

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 he needs (and this is what FeedXL is designed to help you with!).

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:

  1. Long periods of time without feed – if you are feeding your horse in meals, and there are long periods (more than four hours) where he goes without something to eat, his 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 ulcers (see https://feedxl.com/8-avoiding-gastric-ulcers/).
  2. 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 (see https://feedxl.com/starch-ulcers-whats-the-deal/).
  3. 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 (see https://feedxl.com/18-feed-cooked-grains/).
  4. 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, weight loss, diarrhea, poor hoof quality (increasing his 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 (see https://feedxl.com/38-the-importance-of-fibre/).

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 take 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 (>15% starch), should 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 should 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 use FeedXL to check which nutrients (vitamins and minerals) are missing and top these up with a supplement or balancer pellet.

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, 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 deveoping 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!

Black horse on brown pasture

How Stress Affects Your Horse’s Gut

Stress! Did you know stress affects the gut? In pretty dramatic ways!

Prof John Pluske presented a talk at this weeks animal nutrition conference looking at the effect of stress on weanling pigs. Here are some photos from his presentation:

Pigs have a very similar gastrointestinal tract to horses so I often look at pig data when trying to solve problems where there is not enough horse specific information to base my research on.

Prof Pluske showed that stress negatively affects a weanlings pigs gut. With the guts ability to repair itself and it’s effectiveness as a barrier between gut and body both being damaged by stress. Essentially when a piglet is stressed the gut gets damaged. But it then can’t fix itself and it starts to leak.

Which seems relevant to horses. I am sure that we see this in horses too and with the similarities in gut physiology it seems logical… which means we need to be really aware of how we feed and how that impacts on gut health, particularly when a horse gets stressed.

Three things that are really important:

1. Feeding a fully balanced diet that meets all nutrient requirements so the gut has the nutrients it needs to remain intact.

2. Feeding lots of forage. Forage is high in fibre and supports the population of good bacteria in your horse’s gut. These bacteria are very involved in maintaining overall gut health; and

3. Feeding high quality protein. The gut has huge requirements for specific essential amino acids. These amino acids are used by the gut to repair and to produce protective mucus. To provide optimum levels of these amino acids you need to use ingredients with high quality protein.

Protein quality is so important for many reasons. To learn more read our post ‘Understanding Protein Quality’.

Questions? Comments?

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Horse on summer pasture

What You Should Know About Anaerobic Fungi

Anaerobic Fungi! These little critters live in our horses’ hindguts! And they are responsible for an estimated 30 to 40% of the fibre fermentation that occurs in there! So as well as thinking about how diet might affect our horse’s hindgut bacterial populations we also need to think about how it might affect their anaerobic fungal populations!

Problem is, we know so little about them that we don’t know what is good and what is not so good for them. Information on what we know so far was presented at EEHNC by the incredibly passionate researcher Dr Joan Edwards. Joan described the fungi as having potent fibre degrading enzymes, giving them an important role in a horse’s digestion process.

The fungi can survive outside the horse’s gut too, and are seemingly resistant to both oxygen (which kills many anaerobic bacteria that live in the hindgut) and desiccation (drying out). This makes me wonder if they are part of the reason why my horses will seek out specific dry manure piles and eat them on occasion… maybe?!

Anyway, there is some research published (e.g. https://www.researchgate.net/…/329954798_Anaerobic_fungal_c…)

And more research to come (https://www.wur.nl/en/project/Equine-Anaerobic-Fungi.htm)… so watch this space as we keep learning more.

In the meantime while we figure out how to look after these fungi, I suspect feeding in the way that will look after the bacteria in a horse’s hindgut will also look after the fungi… so keep your horse’s diet high in low fructan forage, keep grain/starch out of the hindgut by feeding only well-cooked grains where necessary and in as small meals as possible and make changes to the diet slowly.

I love info like this as it is exciting to know we are always understanding horses better. Part of me though is thinking great, yet another thing we have to think about! ?

Questions? Comments?

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Gastric Ulcer Medications and Their Effect on Digestion

Q: Does gastric ulcer medication reduce nutrient digestion in horses?

Someone asked me this in a recent seminar and it reminded me that when I was studying during my PhD tenure we had looked at the effect of pre-incubating grains in equine stomach fluid on the digestion of starch from those grains.

And what we found was that starch from grains that were exposed to equine stomach fluid before being digested by small intestinal enzymes was between 17% (extruded rice) and 104% (cracked triticale) MORE digested than starch that wasn’t exposed to the stomach fluid. So the stomach fluid was having a definite positive influence on the digestion of starch.

What we can’t say from this research was how much of this increased starch digestion was due to the stomach acid and how much was due to the protein digesting enzymes the are present in stomach fluid that would be starting protein digestion and making access to the grain starch easier for the starch digesting enzymes in the small intestine.

The thing to remember though is that the protein digesting enzymes in a horse’s stomach fluid rely on the stomach acid to activate them. So regardless of whether the improved digestion was due to the acid itself or the protein digesting enzymes, if you stop acid production using ulcer medications you will lose both the acid and the enzymes.

So, if we use medications like ranitidine and omeprazole to reduce gastric acid secretion in horses we are very likely reducing the digestion of at least some nutrients further down the gastrointestinal tract.
What to do??? Well, if your horse has ulcers this is by far the most important consideration, you need to medicate to get rid of the ulcers as quickly and as effectively as you can.

BUT, once the ulcers are gone it is recommended you use good management practices to keep your horses chewing, their stomachs full and buffered with saliva and their minds calm instead of constantly using medication to prevent ulcers. That way you are allowing their gastrointestinal tract to function the way it was designed (albeit I would love the opportunity to redesign parts of their gut!) and allowing the digestion process to be as effective as possible.

More info on feeding to prevent ulcers in our article ‘Avoiding Gastric Ulcers’ here https://feedxl.com/8-avoiding-gastric-ulcers/

Happy to share the method for the in vitro assay used to conduct this work with anyone who would like the details!

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The Link Between Regular Forage Meals and Gut Health

Poet and I (Nerida) headed out a few weeks ago to do some real work mustering sheep (not that we did anything useful, we were just along for the ride!). There were 5 of us on horses, saddled up by 6:30 am and in incredibly steep, rocky, tough (but stunning!) terrain for 6 hours. At various points we dismounted and slid (feet sideways) down parts of the mountainside because it was too steep to ride. Sheep were tripping and rolling down the hill (amusing! but gives you an idea of how steep it was!!).

Anyway, here is me, very conscious of gastric ulcers, giving my horse lucerne/alfalfa as I saddled up, letting him pick what grass we could find while out riding if we were stopped for any time so he at least salivated a little bit and immediately giving him water and more lucerne/alfalfa on return to where we had saddled up… meanwhile stifling my panic at watching the other horses eating nothing and trying not to think too much about what was going on in their stomachs.

I asked one of the guys, an experienced horseman, if he worried about ulcers, and it soon became clear that there was no understanding of how a horse’s stomach worked and the negative impact of not feeding them for such long (long!) periods of time (his horse had a couple of hours trip home).

I also asked recently at a seminar who could confidently sketch a horse’s gut or explain how it works and no-one was able to. And I get this… I had no idea what a horse’s gut looked like or how it worked the entire time I rode in my pre-nutritionist life!

The thing is, a horses stomach never stops secreting gastric acid. So even when your horse is not eating it is filling the lower part of its stomach up with acidic gastric juices. While the stomach is full this isn’t an issue as the dense matt of fibre in the gut will stop the acid from splashing around and burning the unprotected lining of the upper section of the stomach.

Problems start though when horses are off feed for long periods like this and end up with a pool of acid and an empty stomach. Combine that with the movement of being ridden and you get acid splashing up and quite literally burning holes (causing ulcers) in the top part of the stomach.

So here is my plea! Please help us to educate people on how a horse’s stomach works and what they can do (really simple things) to keep their horse’s stomach and therefore their horse healthy and pain free. Share this article on Avoiding Gastric Ulcers with them and have them understand that a horse’s stomach should never be empty and that as much as is practical you should never work a horse on an empty stomach.

Thank you!! From us and from all of the horses who will be so much better off when their owners understand how they work just a tiny bit better.

The Impact of Proton Pump Inhibitors on Gut Bacteria

An interesting read about the impact of proton pump inhibitors (PPI) like Omeprazole (the major drug we use to treat equine gastric ulcer syndrome) on the gut bacteria in humans! https://gut.bmj.com/content/early/…/12/09/gutjnl-2015-310376

While these drugs are a huge help in setting up an environment in the equine stomach where ulcers can heal, they are overused in many horses (some racehorses are never taken off these drugs) to prevent ulcers in place of management systems that will reduce a horses risk of ulcers (like feeding a forage meal to fill the stomach prior to work).

Makes me wonder what PPIs may be doing to the equine gut bacterial populations… one study I can find (https://onlinelibrary.wiley.com/doi/pdf/10.1111/eve.07_12792) shows no impact on equine fecal bacterial populations, but use of omeprazole in these horses was only short term and the study doesn’t specify the dose used. The fecal microbiota also aren’t necessarily reflective of what is happening further up the gastrointestinal tract.

Something to keep in mind if you have a horse on a PPI medication long-term. Needs some more research!

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Hindgut Ulcers

There has been a bit of talk about hindgut ulcers in recent years; do they exist, what impact are they likely to have on a horse, how should we treat them, how do we even know if they are there… lots of questions, not a lot of answers.

But here is something for you to consider… I just spent the end of last week in a room full of dairy (as well as pig and poultry) nutritionists. They spoke a lot about sub-acute rumen acidosis (SARA) and part of that discussion was around the health of the rumen wall and the impact that SARA has on it. Essentially if you make the rumen acidic (in the same way we can make a horses hindgut acidic when we feed raw grains like corn/maize), you start to damage the gut wall. Initially this will reduce the gut linings ability to asorb nutrients (which is a huge problem in itself). BUT, make it bad enough and ulcers will appear!

The photos here (from https://vet.uga.edu/…/digest…/week02/forestomach/rumen06.htm) show rumens that have been affected by acidosis. The first (black) shows ulcers in the lining. The second shows a healed ulcer and the long term damage done.

Scary huh!!! Please when you feed think about how what you are feeding is going to affect your horse’s hindgut health. It is possibly the single most important thing to consider when feeding!

For more on feeding for hindgut health have a read of our newsletter Keeping the Hindgut Healthy at https://feedxl.com/15-keeping-the-hindgut-healthy/

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How to ‘Measure’ Gut Health

Gut health! It’s so important but also really hard to ‘measure’. One way to get a bit of an indication of what your horse’s hindgut health is like is to check faecal pH.

A healthy hindgut will stay at quite a neutral pH, close to 7. At this pH the good fibre fermenting bacteria will be living happily ever after and doing an amazing job of digesting fibre for your horse.

A high pH (over 8) may indicate that there is not a lot of fibre fermentation happening in the hindgut for some reason, while a low pH (less than 6.5) may indicate that there is too much fermentation of starch and sugars happening. The good fibre fermenting bacteria don’t like living in these lower pH conditions and will be starting to shut down. If pH goes below 6.2 you can be almost certain that a lot of your good fibre fermenting bacteria will be starting to die and your horse will lose the ability to digest fibre (which then causes all sorts of problems including weight loss and vitamin deficiency).

So if you want to do a quick check on hindgut health, grab a ‘soil pH test kit’ (google that, you will find plenty of options for inexpensive kits) and use it on a fresh pile of your horse’s manure. You might find that pH is just right, or you may just find that something is a little out of kilter and you need to adjust the diet to get it back to a more neutral pH.

Have fun! I spent three years of my life measuring faecal pHs, fond memories! ?

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Enzymes, What Do They Do for Your Horse?

When a horse eats, much of its feed is made up of LARGE carbohydrate, fat and protein molecules. The horse can only absorb tiny little molecules from its gut (because if big stuff was able to cross from the gut into your horse’s body all sorts of bacteria, toxins and general muck would pass into the body and cause disease havoc!).

So before absorption from the small intestine can occur, the big stuff must be chopped up into little stuff. And it is enzymes in your horse’s gut that do this chopping.

It is easiest to think of digestive enzymes as little pairs of scissors. Let’s look at starch as an example. Starch (found in cereal grains like barley and corn/maize) is made up of lots of glucose molecules, all joined together. The job of the starch digesting enzymes in your horse’s small intestine is to cut starch into single pieces of glucose. Then it is the glucose that your horse is able to absorb.

Each nutrient has its own specific set of enzymes in your horse’s small intestine. So there are specific enzymes to digest/chop up starch, protein and fats/oils.

To learn more about enzymes and your horse’s digestive system, read https://feedxl.com/31-the-gastrointestinal-tract/

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Gut Bacteria, Vitamin B1, and Behaviour: Are They Linked?

The short answer is yes! Here is how:

Vitamin B1 has been observed to have an influence on behaviour in multiple animal species, including horses. A horse will meet its vitamin B1 requirements via the vitamin B1 it eats in its diet and from vitamin B1 produced by the bacteria in its hindgut.

There are two main families of bacteria living in your horse’s hindgut:

1. The fiber fermenting bacteria who love to ferment fibre from the forage your horse eats. These little critters are the ones we consider the ‘good bacteria’; and
2. The starch and sugar fermenting bacteria who prefer to ferment starch and sugars. These we generally consider to be the ‘bad bacteria’.

The good bacteria PRODUCE vitamin B1 that your horse can then absorb and use.

On the other hand, the bad bacteria produce a compound called ‘Thiaminase’ that actually destroys vitamin B1 (also known as thiamine) that is in the gut, making it useless to your horse.

If your horse has too many bad bacteria, and not enough of the good ones your horse may not get enough vitamin B1 and behavioural changes may occur.

How do you avoid this? Keep your horse’s hindgut healthy with an abundant population of good bacteria. The main two things you should do to achieve this are:

1. Feed lots of forage!; and
2. Never feed uncooked grains (with the exception of oats for some horses)

For more tips on keeping your horse’s hindgut healthy head on over to https://feedxl.com/15-keeping-the-hindgut-healthy/

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