Horses have a digestive system designed to manage a slow, steady intake of small amounts of forage. When this inherent grazing behaviour is disrupted by changes to diet, environment and other stressors – mainly by the actions of humans – horses often suffer digestive problems, one of the most common being ulcers. Ulcers are essentially intestinal sores that won’t heal. Two types affect the horse’s gastrointestinal system: gastric ulcers are lesions in the stomach wall, while colonic ulcers form in the hindgut, specifically, as the name suggests, in the colon. Horses can suffer from both simultaneously, but gastric ulcers occur more regularly.


A horse’s stomach is small and comprised of two halves. The lower stomach, which is called the glandular mucosa, consists of a thick protective lining and glands that continuously produce large amounts of digestive acid (about 1.5 litres an hour) to help digest what is, by nature, supposed to be a perpetual intake of chewed forage. The upper stomach, the squamous mucosa, has a thinner lining and minimal protection from stomach acid. This is where most gastric ulcers form.

Although any horse, no matter their breed, age, sex or level of exercise, can have ulcers, performance animals are particularly prone. This is because stress of any type – due to transport, changes to routine, stall confinement, for example – is the main risk factor in ulcer development. Studies even show that stress from strenuous exercise itself not only increases the production of stomach acid but movement causes the acid to splash up into the vulnerable upper stomach.

Twice-a-day feeding schedules and limited grazing are also problematic. Because the lower stomach still produces acid even when the horse isn’t eating, prolonged periods without saliva, which is the upper stomach’s only buffer against acid, cause irritation and potentially ulcers.

High carbohydrate rations can also exacerbate the possibility of ulcer development. Horses are designed to eat fibrous plants, not grains full of sugars and starches. Grain-based feeds increase production of a hormone called gastrin that stimulates the stomach to produce acid. Combined with the fact these feeds are quickly consumed with far less chewing than forage, means less acid-neutralizing saliva is produced to protect the stomach.

“High carbohydrate feeds are quickly fermented by bacteria within the stomach. This process produces a large amount of small acids (volatile fatty acids or short chain fatty acids), which work with the stomach acid to damage the stomach lining,” said Dr. Bri Henderson, BVMS MRCVS, of Cheltenham Veterinary Centre. “Coincidently, this is also one of the mechanisms behind colonic ulcers. When these pesky VFAs spill over into the small intestine and hindgut and slowly change the environment pH, it becomes more difficult for the bacteria that live in the hind gut normally to survive.”

Another ulcer cofactor is non-steroidal anti-inflammatories (NSAIDs) such as phenylbutazone (bute), or flunixin megulmine (Banamine©). These drugs prevent effective production of the stomach’s mucosal lining, leaving the stomach open to the damaging effects of acid. Long-term NSAID use is said to be the main cause of the less common lower-stomach – or glandular – ulcers.

Signs of gastric ulcers may be non-existent or quite subtle. Some horses may show:

  • Changes in temperament, irritability, tooth grinding
  • Altered performance, resistance to work, “behaviour issues”
  • Loss of appetite, weight loss
  • Poor condition, dull coat
  • Recurring mild colic


The only way to get a definitive diagnosis is by gastric endoscopy (gastroscopy), whereby a three-metre long tube with a small camera and light attached is inserted into the stomach via the nostrils and esophagus.


Food is passed from the stomach to the hindgut, or large intestine, which includes the cecum and colon. Here, bacteria and other micro-organisms break down fibre through fermentation to produce volatile fatty acids, which provide the horse with the majority of his energy requirements. Ulcers can result when this process is altered.

Long-term NSAID administration and stress appear to be the main culprits in colonic ulcer development, especially right dorsal colitis, a term for ulcers in the upper-right part of the colon. High-grain and/or low-forage diets may also be implicated. When large quantities of undigested carbohydrates reach the hindgut, lactic acid is produced. This increase in acid – called hindgut acidosis – kills off beneficial digestive micro-organisms, releasing toxins and allowing pathogens to proliferate. This activity reduces mucous production, leaving the hindgut unprotected.

While some symptoms can be similar to those of gastric ulcers, there are often specific signs there is a problem in the colon:

  • Repetitive behaviour such as weaving, cribbing
  • Girthiness
  • Flank sensitivity
  • Resistance to grooming, blanketing
  • Difficulty bending, collecting, extending
  • Diarrhea

Diagnosis is difficult. Endoscopes can’t reach the hindgut and rectal exams don’t usually reveal much. Ultrasound in combination with blood work changes are probably the best diagnostic tools. “The normal colon wall has a distinct appearance and thickness, so ultrasound can help detect inflamed colon wall, which is a good indication of ulcers,” noted Dr. Henderson.

Ulcer Prevention and Non-medical Management

Allow horses to live as natural a life as possible and minimize stressful situations such as trailering, showing and intensive training.

Provide daily turn out with other horses. But watch for “bullying” by turn out mates. If stalled, ensure horses can at least see their friends if not be able to touch and play with them to reduce isolation stress.

“I believe it is important to manage our horses appropriately and ensure that they get time to ‘be horses.’ Paddock turn out, consistent management schedules, hacking and rest periods during the competitive season will all help to mitigate the stress that our competitive horses are under,” Dr. Henderson added.

Offer access to forage 24-7 to mimic a horse’s natural feeding pattern. In the case of colonic ulcers, it may be suggested that feeding hay be reduced or eliminated to ease the digestive burden on the colon and allow healing. Switch to pelleted forage or soaked alfalfa cubes. They have less volume and digest easier and quicker.

Reduce or eliminate grains and concentrates. If you must feed grain, feed four or more small meals a day. Ensure the stomach has some forage in it before exercise to help absorb stomach acid.

Decrease NSAIDs or stop using altogether as directed by your veterinarian. “Often NSAID-induced colon ulcers are seen as colic cases for ‘right dorsal colitis.’ These can be painful enough to make you think they are surgical,” said Dr. Henderson.

Ulcer Treatment Options

While lifestyle changes are necessary for a permanent recovery, there are medications available to help the process along

by Dr. Bri Henderson

One of the most commonly prescribed medications for performance horses is omeprazole (Gastrogard®). Stomach ulceration occurs in 66 to 100 per cent of equine athletes, from racing Thoroughbreds and endurance horses to eventers, hunter/jumpers and dressage horses.

Omeprazole belongs to a class of drugs called proton pump inhibitors. They act to reduce the amount of acid secreted into the stomach and thus aid in healing ulceration of the stomach lining (mucosa).

While it is an effective remedy, there are risks associated with administering omeprazole. Recent human literature demonstrated that patients on long-term omeprazole had reduced calcium absorption and subsequently reduced bone density. In human studies, long-term omeprazole also reduced protein digestion along with reduced absorption of vitamins/minerals (magnesium, calcium, B12). The results of these studies created concern amongst equine researchers that our equine athletes may be at risk of similar problems.

One equine study found that horses placed on 60 days (short-term) omeprazole had no alteration of calcium metabolism and no change in bone density. In contrast, another study out of the Kentucky Equine Research Centre (KER) found that calcium digestibility was reduced by 15 to 20 per cent in horses on omeprazole (no change in magnesium, iron, protein or fat was noted). The KER study also reported a major increase in a hormone called gastrin, which is produced by the stomach to stimulate acid secretion. Elevated levels of gastrin can also impact other hormones in the body to draw calcium from bone in order to maintain blood calcium levels. Further research is needed to explore these changes more thoroughly.

Omeprazole has been successful in 70 to 77 per cent of cases of gastric ulcers and so it is important to be aware of alternative options.

Ranitidine is another type of drug which can be prescribed. Instead of slowing the ultimate production of acid, H2 blockers such as this act earlier on in preventing the stimulation for acid production. They are thought to be less effective for horses in intense training, however, they do offer a more economical option to Gastrogard® and may be a good alternative in the 30 per cent of cases which do not respond to omeprazole.

Sucralfate is also often added to a treatment plan for stomach ulcers. This medication binds to ulcerated areas of mucosa and stimulates mucus production and blood flow to the stomach lining. It is best used in short-term treatment plans and may become less effective over time.

Numerous supplements exist to support stomach and colon health, but often the science can be lacking. Interestingly, antacids alone showed little benefit with a less than a two-hour reduction in acid relief. Fruit fibre (pectin/lecithin) complexes showed inconsistent benefit in preventing stomach ulceration when used on their own.

There is some research suggesting that fruit fibre, saccharomyces yeast and an antacid supplemented together is beneficial, however, further product development and independent research needs to be done in this field.

While pleasure horses are less likely to develop stomach or colon ulcers, they are not immune to them. Changes in your horse’s personality, willingness to work or body condition/top line should always be investigated to rule out a source of pain. Ensuring that all horses live on a balanced high forage, low-sugar diet with consistent opportunities to ‘be horses’ is the best way to keep them happy and healthy.

Regardless of the job your horses have, the underlying message is treatments should be targeted at healing and then supplements and management changes instituted to maintain and prevent further ulceration.