Stomach Ulcers

February 2, 2023 61 view(s)
Understanding your horse's stomach 
  • Stomach – The stomach of the horse contains about 10% of the capacity of the small intestine (compared with 70% for cows). Therefore, horses cannot handle large amounts of feed and must eat frequent, small portions.
  • Esophagus – A muscular tube that carries food from the mouth to the stomach. In the horse, food only moves one way down this tube; horses cannot throw up.
  • Squamous mucosa – Covers approximately one-third of the equine stomach and is void of glands. The texture of the healthy cells in this area feel like the skin on the back of your hand. Ulcers most regularly occur in this region near the margo plicatus curvature.
  • Margo plicatus – The folded ridge of the mucous membrane between the stomach’s nonglandular portion and the glandular portion.
  • Glandular mucosa – Covers the remaining two-thirds of the stomach and contains the acid-producing glands. Ulcers are less prevalent here (but still possible) due to having more protective factors.
  • Pylorus – Lower portion of the stomach that leads into the small intestine.
  • Duodenum – Uppermost part of the small intestine that plays an important role in the digestive function. Carries partially digested food out from the stomach.
    Acid-stimulating receptors – Trigger an “acid pump” to secrete acid. Sensitive to diet and stress.

Your horse’s stomach is relatively small and designed to continuously produce acid from millions of acid pumps – up to 16 gallons a day – to digest small, frequent meals.1 In a natural grazing scenario, grass and saliva are constantly present to buffer and help pass acid from the stomach.

When horses are stalled with limited turnout and fed fewer, larger meals, acid levels increase. Higher intake of grain and stress from training, showing and even changes in their routine can stimulate acid pumps to increase acid levels even more.2,3,4,5,6 As levels rise, acid can reach the unprotected squamous mucosa where it can eat through the lining.

The resulting stomach ulceration often suppresses appetite, so the horse may eat even less buffering roughage. This creates a vicious cycle of increased acidity. 

Your veterinarian will use an endoscope**, a tiny camera attached to a long, thin tube, to examine the inside of your horse’s stomach for ulcers. If endoscopy is not practical, then a presumptive diagnosis may be made based on clinical signs, history and a physical examination.

**Endoscopy, or “scoping,” is a procedure that lets your veterinarian look inside your horse’s stomach via a tiny camera attached to a long, thin tube. Your veterinarian will place the endoscope in through the nostril, then down the esophagus and into the stomach. There, the lining can be examined for the presence of ulcers. If endoscopy is not practical, then a presumptive diagnosis may be made based on clinical signs, history and a physical examination.



The only definitive way to determine if your horse has an ulcer is by having a veterinarian use a 3-meter endoscope, or “scope,” to look inside the stomach. Not every veterinarian has this specialized equipment, so Merial sponsors a number of diagnostic events at veterinary clinics and university campuses nationwide. If endoscopy isn’t available, your veterinarian may make a presumptive diagnosis based on history, outward signs – such as changes in eating and drinking, changes in attitude, weight loss or recurrent colic – and a physical exam.


Endoscopy events in 25 states identified stomach ulcers in a surprising number of horses:

  • 58 horses participated in total
  • Horses from 1 to 41 years old were identified with stomach ulcers
  • 254 horses that were diagnosed with stomach ulcers had no previous history of ulcers
  • Horses with stomach ulcers were stabled in a wide range of environments, including box stalls, pipe stalls, a pasture alone and a pasture with other horses
  • Horses fed supplements like beet pulp, flaxseed and corn oil were still identified with stomach ulcers
  • Stomach ulcers were found in horses across a variety of disciplines

Stomach Ulcer Prevalence by Discipline

  • Racing - 92%
  • Harness - 86%
  • Saddleseat - 82%
  • Reiners - 76%
  • Cutting Horses - 69%
  • Show Jumpers - 67%
  • Eventers - 62%
  • Hunter Jumpers - 60%
  • Western Pleasure - 52.9%
  • Barrel Racing - 51%
  • Dressage - 44%

What Endoscopy Reveals
When diagnosed by a beterinarian with an endoscope, stomach ulcers are graded from 0 to 3

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