Monthly Topic: The Digestive System

Thanks to Blade I have educated myself extensively on gastric ulcers. I’ve talked about them often throughout the years, and even developed my own way of handling them.

I have talked briefly about them in one of my popular articles, Horses Update, so I thought it was fitting to start this year’s new monthly theme with a deeper look at the digestive system! Actually, we’re going to begin with digestion and over the next 3 months we will work toward ulcers and what I’ve done to help my gentlemen.

This is something I am quite passionate about so it’s going to be a multi-part series. I know it’s long but it’ll be worthwhile (I hope). Going forward my future monthly research won’t be this long (I also hope).

Thanks for sticking with me, I love you all!!!!


Ulcers are extremely prevalent in today’s horses. We ask them to perform and conform to our daily lives when the reality is horses have not evolved to do any of these things. Horses in the wild roam many miles per day, eat all day long, and eat grasses. They don’t sit around, they don’t perform strenuous athletic activities unless required to, and they don’t eat grains or fortified feeds. In order to understand why ulcers are so common and how to correct them we need to understand first how the horse works.

Horses evolved to eat grasses many hours each day. Their digestive systems are built for it….small amounts….allllll day. Through history they have evolved to create 1.5 liters of stomach acid EVERY HOUR to break down the fibers that should be coming in on the regular. That’s a whole lot of acid (almost 10 gallons per day); since horses are grazing animals their saliva works to buffer that acid. Horse saliva contains calcium (more than most mammals) and in any given day they can create 9-11 gallons of saliva that works to create a happy digestive system (assuming they are grazing and chewing normally as nature intended).

A horse makes 1.5L of stomach acid EVERY HOUR

When you design a feeding program it should revolve around THIS; we cannot change their biology. It may not be convenient but it’s also inconvenient to work with a horse who is too uncomfortable and unhappy to perform to the best of its abilities. It’s inconvenient to have a horse that hates its job because its tummy hurts.


The horses stomach is small…only 8-15liters (or 2-4 gallons) in size. The upper (proximal) half is called the squamous mucosa (non-glandular) region and has very little protection against the harsh acidic environment. Most cases of ulcers occur in the upper region where protection is low.

The bottom (distal) half of the stomach is called the glandular mucosa; it is protected from the acidic environment by a lining of gastric mucous. The stomach is where acid is secreted to begin digestion.

From the stomach, contents are pushed into the small intestine. The small intestine is where most of the sugars, proteins, and fats are broken down. Essentially any grains or commercial feed will be broken down and digested by the end of their 70-foot journey through the small intestine. We then move on to the HINDGUT.

Contents empty from the small intestine to the cecum where billions of microbes break down the fibrous material that remains. This is from the forage…hay and grass. Forage is made of more complex fibrous materials that take longer to digest. Here, the material will ferment for about 7 hours.

Side Note: When temperatures drop horses generate their own heat through the fermentation in their hindgut. For this reason it is critical to make sure horses have plenty of extra hay in cold weather.

Digestion continues into the large colon. More fermentation is done and some vitamins and minerals (B group vitamins, phosphorus) are absorbed. Feed can stay here for 2-3 days. At this point contents are passed through the small colon and eventually excreted.

The important thing to note here is that grains and concentrates don’t typically (SHOULDN’T) make it past the small intestine. Forage is the KEY for digestion through the hindgut (cecum, large colon).


In captivity horses are often fed meals. They eat their grain, eat their hay, and wait on their next meal.


1: Grains….Cereals…Concentrates (oats, barley, corn, commercial feeds) are processed differently in the stomach. These types of feeds are absorbed in the stomach and give off volatile fatty acids (VFAs), alcohol, and lactic acid.

2: Grains and cereals, etc are processed faster than forage. The contents are broken down quickly and leave the stomach. Forage, however, stays longer in the gastrointestinal tract as the body works to break down more complex fibers

3: If the horse isn’t chewing it isn’t producing much saliva. When horses are given intermittent meals and run out of hay they are spending time not producing saliva. More acid is being created without the food and saliva to buffer it. Add in the cortisol from stress of wanting food and you’ve got a recipe for ulcers


How much a horse eats in one feeding matters just as much as how often.

A horses stomach is only 8-15 liters (2-4 gallons) in size, they are made to eat small amounts all day long. They aren’t made to have the large meals we serve them.

Even before I ditched the commercial feeds I kept serving sizes small

If you overload a horse’s stomach some of the starch will pass through the stomach undigested. It will then get digested by the microbes in the hindgut.

The hindgut is where fiber is meant to be processed. It consists of an entirely different environment and is inhabited by entirely different microorganisms. When starch enters this area and creates the fermentation products of acid and VFAs, it creates a hostile environment for the fiber-loving bugs. This creates an imbalance and the starch loving bugs can outcompete the other microbes since they prefer the acidic environment.

Studies have shown that keeping meals limited to under 200g starch/100kg Bodyweight (BW)/meal is a safe option with less than 50g/100kgBW/meal reaching the hindgut. Conversely, when meals exceeding 200g starch/100kgBW/meal as much as 70-150g/100kgBW/meal can reach the hindgut. The horse’s metabolism is simply too fast to make use of large meals. This is why smaller meals more often is best practice. They are made to graze.

Things To Keep In Mind

With what we know from today, there are a few things to keep in mind to creating the ideal environment for your horse.

  • Small meals more often: Don’t feed too much at once, remember the stomach is small
  • More forage, less concentrates: Feed what you need to balance your hay and add enough calories, you don’t need to feed a ton of concentrates.
  • Maximize chewing time: encourage the most chewing time to create the saliva that will buffer stomach acid
    • Slow feed nets and grazing muzzles will work great if you have an easy keeper
  • Extra hay in winter: When the temperatures drop horses need more hay to keep them warm. Heat is generated by fermentation of fibers in the hindgut.

References and Further Reading


  1. Fantastic info I have found spreading the feed out throughout the day stops them gorging. With all the rain we’ve had people have to beware of sand colic & foundering as there is sooo much grass now which is a great problem to have. I do so look forward to your blogs. Have a wonderful weekend ahead.

    Liked by 1 person

    1. Thank you!!! I would be thrilled to have so much grass right now! We are going through the aftermath of a dry summer (great for riding haynotsomuch). Hay is scarce and price gouging is REAL. Founder is indeed a frightening thing though!

      Liked by 1 person

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