08/01/2025
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Colonic Ulceration in Horses
Brian S. Burks, DVM, Diplomate, ABVP
Board-Certified in Equine Practice
Ulceration of the large colon of horses is a syndrome with an incompletely known etiology. Right Dorsal Colitis (RDC) secondary to NSAID administration is the most recognized form of colonic ulceration. Clinical signs of RDC include weight loss, diarrhea, bouts of colic, anorexia, peripheral edema and profound hypoproteinemia (low total protein) due to protein losing enteropathy (PLE). Colonic ulceration may also occur in the absence of NSAID administration, and the ulcers may form in any of the four quadrants of the large intestine. Performance horses that are fed diets low in roughage and high in grain are thought to be at risk of colonic ulceration. Available research on colonic ulceration is scarce, largely because visualizing the colonic mucosa in a live horse is not possible.
Gastric ulceration in performance horses is a common and a well-recognized problem, which can only be diagnosed by gastric endoscopy. Performance horses are at risk of developing colonic ulcers; however, colonic ulcers are more difficult to diagnose, as the colonic mucosa cannot visualized. The large colon cannot be completely examined without exploratory surgery or necropsy.
One study involved the necropsy of over 500 horses. One hundred and eighty of these horses were known to be performance horses, and colonic ulcers were found in 63% of these horses (87% had gastric ulcers). In the remaining group of horses, 44% had colonic ulcers and 55% had gastric ulcers.
The prevalence of gastric ulcers in the performance horses in this study approximated the prevalence of gastric ulcers in performance horses, so the prevalence of colonic ulcers may be higher than was previously thought. Necropsies performed at Fox Run Equine Center often find colonic ulceration. Ulcers have also been noted during endoscopy in the small intestine of miniature horses overdosed with phenylbutazone.
Etiology and Pathophysiology of Colonic Ulcers in Horses
Gastric ulcers and colonic ulcers can both occur secondarily to NSAID administration. Phenylbutazone, administered at high doses, or over a long period of time, poses a particular risk. Phenylbutazone (PBZ) is one of the more commonly used NSAIDs for musculoskeletal pain in horses, and it is a non-specific COX inhibitor (COX 1,2,3- cyclooxygenase), the combination of which contributes to phenylbutazone being closely associated with RDC development. Many NSAIDs can induce RDC, mainly PBZ, flunixin meglumine and ketoprofen. The COX-2 selective inhibitors such as meloxicam and firocoxib may cause ulcers when administered at doses well above the recommended dose, but are well-tolerated at normal doses and even three times normal doses.
Some horses are thought to be more sensitive to the side effects of NSAIDs and can develop ulcers at normal, and even lower than normal doses. Whether some of these horses have an underlying disease that predisposes them to RDC is unknown. Ulceration tends to be worse in the right dorsal colon; however other parts of the colon may also be affected.
Possible, but unproven, causes of non-NSAID-induced colonic ulceration include:
1. Acidosis of the hindgut from fermentation of carbohydrate-rich foods (i.e., grains) When sweet feed is fed at >1.0% of body weight per day, starch and sugar will not be fully absorbed by the small intestine, spilling over into the colon.
2. Helminth migration or small strongyle larval encysted in the colon wall.
3. Chronic stress resulting in chronically high endogenous plasma cortisol concentrations.
A combination of these factors is likely.
The pathology of colonic ulceration includes mucosal ulceration of varying severity, with thickening of the underlying submucosa and lamina propria resulting from edema and inflammation. Fibrosis and the formation of internal strictures are possible sequelae.
Clinical Presentation of Colonic Ulceration in Horses
All ages and breeds of horses can be affected; however, young performance horses are considered to be at greatest risk. The earliest symptoms of colonic ulceration may be subtle, and could possibly include:
1. Vague signs of abdominal discomfort such as resentment to the tightening of a saddle or resentment to being ridden.
2. Low-grade colic symptoms, that wax and wane. Between episodes, the horse may appear to be normal.
3. Decreased performance.
4. Decreased appetite.
5. Rough dull hair coat.
6. Weight loss.
7. Diarrhea.
With severe disease, the horse may develop ventral and peripheral limb edema, anorexia, colic, lethargy, fever, dehydration and endotoxemia. Complications of severe disease can include laminitis, infarction of the colon, and bowel rupture.
Blood work is useful with colonic ulceration. Hypoalbuminemia is a common feature of PLE. Hypocalcemia usually occurs concurrently with hypoalbuminemia, as a large percentage of blood calcium is bound to albumin. Hematology results are variable and may show an elevated white cell count or a low red blood cell count. Fibrinogen or serum amyloid A may be elevated.
Abdominocentesis findings are non-specific; there may be an increased white cell count and increased total protein, depending on the severity of disease.
Diagnosis for Colonic Ulcers in Horses
An accurate diagnosis of colonic ulceration cannot be made without visualizing the colonic mucosa; however, a presumptive diagnosis can be made based on a combination of the following findings:
1. History of NSAID administration (if there is no NSAID exposure, colonic ulcers cannot be ruled out, especially if the following signs are present).
2. Intermittent colic, especially if combined with diarrhea, weight loss and/or peripheral edema.
3. Hypoalbuminemia
4. Abdominal ultrasound finding of a thickened wall of the right dorsal colon or other areas of the colon.
5. Ruling out of more common diseases, that have a similar presentation, i.e. gastric ulcers, salmonellosis, intestinal parasitism etc.
6. Gastric ulcers can occur concurrently with colonic ulcers. Gastric ulcers are unlikely to cause hypoalbuminemia or diarrhea.
Abdominal ultrasound is able to image a limited portion of the right dorsal colon on the right side between the 11-15th intercostal spaces, below the lung margin and axial to the liver. Normal wall thickness is less than 0.4 cm; horses with RDC may have wall thickness >0.6cm. Although the sensitivity of abdominal ultrasound findings is low, ultrasound is a useful tool in combination with the rest of the physical examination.
Nuclear scintigraphy, using technetium-99m hexamethylpropyleneamine oxime to radiolabel white blood cells, has been described as a method of imaging inflammatory lesions in the large colon. This technology may be available in some specialist centers.
Treatment for Colonic Ulceration
Diet plays a significant role in the health of the equine intestinal tract. Many performance horses are fed diets that are high in grain and low in roughage. This feeding practice leads to abnormal patterns of fermentation in the large bowel and to alterations of the intestinal microbes. Mimicking natural feeding habits (high roughage diets) may go a long way to preventing colonic ulcer formation and may also help treat low-grade ulceration. Horses are continuous grazing animals, so frequent, small meals and/or continuous access to forage help prevent gastric and colonic ulcers.
Horses with moderate-to-severe colonic ulceration should discontinue NSAID medication, using COX-2 inhibiters, if needed, or other pain medication. Stress should be minimized. These horses should be fed frequent, small meals at regular intervals (4-6 times daily), along with a low residue diet to decrease the bulk in the colon during healing (no hay). There are a number of complete feeds available that are low in carbohydrates, but have at least 30% fiber. Short periods of grazing fresh grass (10-15 minutes, 2-3 times per day) are also good for stress levels and to lower the colonic load. Omega-3-rich oils can also be used to provide calories without bulk, and the necessary fats for cell membrane formation. They also help limit inflammation. Psyllium mucilloid is an amylase-resistant fermentable fiber hydrolysed by colonic bacteria into short-chain fatty acids (SCFAs). The SCFAs are an important energy source for colonocytes and can help improve the function of the cells, and promote faster colonic. Sucralfate may bind to the ulcer bed and act as a protective cover over the ulcer; it may stimulate the release of protective prostaglandins. Sucralfate has not been clinically proven with colonic ulcers, and I have not found it to be particularly helpful.
Horses with severe hypoproteinemia and edema benefit from plasma (the acellular portion of blood). Replacing the albumin deficit increases the plasma oncotic pressure, which improves tissue perfusion and helps reduce edema, both peripheral edema and edema in the colon, which benefits colonic mucosal healing. Vetstarch is a less expensive alternative than plasma for increasing the plasma oncotic pressure, but it will not improve the hypoalbuminemia.
Horses with colonic ulcers should be encouraged to drink so as to maintain hydrated intestinal contents. Adding salt to grain, hay, or water often improves water intake.
Improvements in clinical signs should be seen within 1-2 weeks; however the colon will take longer to heal – on average 3-4 months, but some horses take longer to heal. Blood work can be monitored regularly, as improvements in blood albumin concentrations will indicate that the treatment is working.
Medications used to treat gastric ulcers have not been found to be beneficial in treating colonic ulcers. Misoprostol, a synthetic form of prostaglandin E2, is cytoprotective and improves healing. The side effects of Misoprostol include abdominal cramping, diarrhea, sweating, and abortion in pregnant mares (and women- so do not handle this medication if you are, or could be, pregnant).
In cases where abdominal pain from colonic ulceration is severe and uncontrollable, a bypass surgery has been reported that alleviates discomfort.
Prevention of Colonic Ulceration
Administer NSAIDs at appropriate doses and for no longer than necessary. Ensure horses are fed an appropriate diet that constitutes primarily roughage, such as grass, hay and chaff. Continuous access to forage helps to buffer acids in the stomach and colon. Carbohydrate-rich supplements such as grain should only be added to the diet as necessary to fulfill energy requirements- in other words, couch potatoes do NOT NEED GRAIN, only those with consistent exercise that increases energy requirements above what hay/grass alone can provide. Consider beet pulp and Omega-3 rich oils as alternative energy sources to grain. Excessive carbohydrate is dumped into the colon and may lead to hind gut acidosis, causing changes to the colonic microflora and erosion of the intestinal lining. Do not kill your horse with kindness.
Fox Run Equine Center
www.foxrunequine.com
(724) 727-3481
