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Colonic Ulcers in Horses


Sporadic colonic ulcers related to drug use or parasites probably occur all the time and heal on their own without us ever realizing they were there. Concern about colonic ulcers rose to a brief fever pitch in 2005 when a well-publicized article reported that postmortem examinations of 454 horses found colonic ulcers in 45% of nonperformance horses and 65% of performance horses. 

However, these were examinations done on horses that had been killed at a Texas slaughterhouse. Their histories were unknown, including use/performance. Horses that are performing well typically don’t end up in slaughter auctions. Since lameness is a common cause of poor performance, and of horses going to auction, there’s a pretty high likelihood there was use of Bute both before the decision was made to dispose of the horse, and on the day of sale in hopes the horse might look good enough to bring a better price. Those findings aren’t at all representative of horses in general.


Most vets agree the cornerstone of treatment for the most common cause of colonic ulcers, right dorsal colitis, is complete avoidance of NSAIDs, especially Bute, and feeding a complete, pelleted feed without hay. Harmonize is a pelleted and flavored daily supplement for all classes of horses highly recommended to be dressed with your usual grain or complete feed or hay twice a day.

For horses with inflammatory bowel disease who may have allergies/intolerances to  allergenic feed ingredients like soy, corn, alfalfa or wheat products, this may not be enough. Starting with a base diet of pelleted/cubed grass hay from a consistent source, individual items can be added back in once the horse is stabilized.

The symptoms of colonic ulcers are varied and depend on both the duration and severity of the problem. The most common sign, and the one that is most likely to get your attention, is repeated bouts of abdominal pain.

Rectal examinations typically don’t reveal any helpful findings, and many cases are diagnosed as spasmodic/gas colic’s or possible mild impactions, and may be rubbed with mineral oil, treated for a while with Banamine and recover, only to do it again. Aggressive deworming may be tried to no avail. Gastric ulcers may be suspected, may even be found on endoscopy, but treatment for this doesn’t resolve the problem either. If the horse has progressed to the point where he’s losing enough blood protein (albumin) through the ulcerated areas and this is picked up on serum chemistry, focus may be directed to the liver, particularly if there is any mild elevation of liver enzymes, but this isn’t the problem either. It may take several vets before you find one that has dealt with the problem recognizes the symptoms and runs the right tests, or the horse may actually end up in surgery before a diagnosis is made.

Directly examining the horse’s stomach is a lot simpler matter than getting a look at his colon. The large and small colons combined are about 25 feet long. Physical examination and rectal examination may not reveal much more than some increased gas. Short of opening the horse surgically to get a look and do biopsies, diagnostic techniques were largely limited until recently. In 2003, clinicians from the North Carolina State College of Veterinary Medicine published information on using ultrasound to diagnose right dorsal colitis. Because the colon lies close to the body surface, it is easily imaged using ultrasound and a thickened, inflamed wall can be seen. Another test is intravenous administration of radioactively labeled albumin. The manure is then tested to see how much passes into the intestinal tract.

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