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Updated: Aug 21, 2021

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This is a short, straight to the point summary of what’s new and agreed on stomach ulcers.

Let’s just start by thinking that a horse’s stomach is a bucket: this is half full of gastric acid, sitting in there as water would. If we walk with this bucket in hand, chances are we are not going to spill any water, but if we start running, water is going to splash everywhere. The same happens for a horse walking VS a horse cantering. If acid splashes everywhere, it will splash on ulcers, and that hurts.

Now, if we put a double handful of hay in our half full bucket, and we start running, chances are that the hay is going to stop some of the water from splashing everywhere.

There we are - that’s just a simple explanation on why it’s important to give our horses a bit of roughage in the morning before exercise.

Apparently ulcers develop mainly or almost exclusively during daytime, not at night time. Horses like to sleep after 8pm. As a result of that, it is recommended to feed 75% of roughage during daytime, so that the stomach is well buffered when it needs it the most.

A gap of 6 hours or more between meals increases incidence of ulcers, so does feeding high energy cubes before hay. Since these are high in carb content, they are acidic, which obviously can exacerbate ulcers.

Proton-pump inhibitors, in oral formulation (such as Omeprazole or the more advanced Esomeprazole), are still #1 treatment for this condition. An injectable form of omeprazole is now available but this has 1 month withdrawal which makes it impossible to use in racehorses.

To make the feed man’s life more complicated, we now know that feeding anti-ulcer drugs 1h before breakfast in the morning results in the active ingredient being absorbed 3x times more. If you think about it this is kind of big deal. As expensive as these are, reducing the dosage whilst achieving the same effect is great. So if you feel like waking up a bit earlier, it could save you some money. However I’m sorry to inform you, in cases of severe ulcers, I still recommend a full dose, 1x tube daily.

Interestingly, ulcers can affect fatigue levels: in other words they can make horses get tired sooner. Horses with ulcers have a shorter stride and lower VO2max levels (look left).

We don’t fully understand why, however it is thought that stomach pain will reduce chest expansion during breathing (if you have got a heartburn I guess you don’t really want to go for a sprint run), therefore limiting oxygen exchange within lungs, by consequence limiting availability of oxygen to muscles. Another reason to make sure our horses are as ulcer free as possible.

There is no other diagnostic tool or method to diagnose or rule out stomach ulcers in horses: we rely solely on gastroscopy. Luckily this is quite a straightforward, quick procedure, no real downside.

Stomach supplements: my approach is they can’t really hurt but they seldom clear ulcers. They are an aid rather than a cure.


How frequent are they in the population?

It is now estimated that 30 to 100% of thoroughbreds in training suffer from some degree of stomach ulcers.


  • Poor appetite

  • Poor body condition

  • Weight loss

  • Diarrhea

  • Teeth grinding

  • Colic

  • Poor performance

  • Pain when girthing

  • Reluctance to train

Pre-exercise feed?

Yes, it is beneficial. The research to date has been completed by feeding 2 litres of unmolassed chaff. It buffered the stomach and reduced the effect of acid splashes. Also has been shown to be beneficial to muscle and lung blood supply. A double handful of hay before exercise would help protect the stomach wall.

Does field turnout cure ulcers?

Yes and no. Rich spring grass is full of carbs therefore quite acidic and can induce worsening of ulcers. But in the same way, horses at grass don’t have the stress of training and racing to deal with, which helps.

Do probiotics help?

Yes - but they have to be fed for a while before a significant difference is noticed.

What is the VO2Max you are talking about?

VO2max is a value representing how much oxygen your body is using at maximum effort. The higher the better. Higher values mean your body is capable of using more oxygen to fuel muscles. It is used to predict endurance performance and reflects cardiorespiratory fitness. The average 30-year-old person has a value of about 40-45; Mo Farah has got a VO2max value of about 80. To achieve high values, muscles, lungs, heart, all have to work to their best.

Do you feel like reading a bit more about it?

Click on the link below brave person. It will take you to the current consensus on stomach ulcers. Not for the faint-hearted:

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