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Colonic Ulceration in Horses

Ulceration of the large colon of horses is a syndrome that is not yet completely understood by veterinary researchers. Right Dorsal Colitis (RDC) secondary to NSAID administration is the most recognized form of colonic ulceration. RDC, in its most clinically obvious form, manifests as a syndrome of weight loss, diarrhea, colic, peripheral edema and profound hypoproteinemia. Researchers believe that colonic ulceration may also occur in the absence of NSAID administration, and that the ulcers may form in any of the four quadrants of the large intestine. Available research on colonic ulceration is scarce, largely due to the difficulty of visualizing the colonic mucosa in a live horse. Some conclusions may be drawn based on what we do know about RDC and related research on equine gastrointestinal health and management.

Performance horses that are fed diets low in roughage and high in grain are thought to be at risk of colonic ulceration.

Introduction to Equine Colonic Ulceration

Gastric ulceration in performance horses is a common and a well-recognized problem, which can be diagnosed by gastroscopy. Performance horses may also be at risk of developing colonic ulcers, however colonic ulcers are more difficult to diagnose, as the colonic mucosa cannot be easily visualized. The large colon cannot be completely examined without exploratory surgery or necropsy.

Pellegrini (2005) conducted a study that revealed how prevalent colonic ulceration actually may be. Dr. Pellegrini’s study is currently the only published, large-scale research that has been performed on this disease. The study was performed at a Texas abattoir, and 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.

Given that these horses were presenting to an abattoir, the study results do not necessarily reflect the general horse populations, and the reasons for the horses being taken for slaughter were not always available. However, the prevalence of gastric ulcers in the performance horses in this study did approximately reflect the upper limit of what we now know about the prevalence of gastric ulcers in performance horses, and so it gives some credence to the fact that the prevalence of colonic ulcers may be higher than was previously thought.

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 is one of the more commonly used NSAIDs for musculoskeletal pain in horses, and it is a non-specific COX inhibitor, the combination of which contributes to phenylbutazone being closely associated with RDC development. Many NSAIDs can induce RDC, including the COX-2 selective inhibitors such as meloxicam, but this usually only occurs when administered at doses well above the recommended dose.

Some horses are thought to be more sensitive to the side effects of NSAIDs and can develop ulcers at lower doses. Whether some of these horses have an underlying disease that predisposes them to RDC is not known (Jones 2009).

Ulceration tends to be worse in the right dorsal colon, however other parts of the large colon may also be affected. Researchers are currently considering the possibility that colonic ulcers may also occur in the absence of NSAID administration.

Possible, but unproven, causes of non-NSAID-induced colonic ulceration include:

  • Acidosis of the hindgut from fermentation of carbohydrate-rich foods (i.e. grains),
  • Helminth migration or encystment in the colon wall,
  • Chronic stress resulting in chronically high endogenous plasma cortisol concentrations.

A combination of these factors is also a possibility.

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 (Jones 2009).

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:

  • Vague signs of abdominal discomfort such as resentment to the tightening of a saddle or resentment to being ridden.
  • Low-grade colic symptoms, that wax and wane. Between episodes, the horse may appear to be normal.
  • Decreased performance.
  • Decreased appetite.
  • Rough dull hair coat.
  • Weight loss.
  • Diarrhea.

With severe disease, the horse may develop ventral and peripheral limb edema, inappetence, worsening colic, lethargy, fever, dehydration and endotoxemia. Complications of severe disease can include laminitis, infarction of the colon and bowel rupture (Jones 2009).

Biochemistry is useful with colonic ulceration since hypoalbuminemia is a common feature of generalized colonic disease. Hypocalcemia usually occurs concurrent to hypoalbuminemia, as a large percentage of blood calcium is bound to albumin. Hematology results are variable and may show an elevated white cell count, with possible elevated fibrinogen or serum amyloid A.

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 could 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. Positive result to fecal blood and albumin test (see below)
  5. Abdominal ultrasound finding of a thickened mural wall in the right dorsal colon (see below), or other parts of the colon.
  6. Ruling out of more common diseases, that have a similar presentation, i.e. gastric ulcers, salmonellosis, intestinal parasitism etc.

Gastric ulcers can occur concurrently with colonic ulcers, however gastric ulcers are unlikely to cause hypoalbuminemia or diarrhea.

Abdominal ultrasound. A limited portion of the right dorsal colon can be imaged using a 3.5-5 MHz transducer, 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 (Barton 2011). The sensitivity of abdominal ultrasound findings is not high; ultrasound is however a useful tool in combination with the rest of the physical examination.

The SUCCEED Equine Fecal Blood Test (Freedom Health) can detect the presence of hemoglobin and albumin in horse feces; this indicates damage to the intestinal mucosa with protein and/or blood leakage. If both hemoglobin and albumin (or only albumin) are present in the feces, the test has a high specificity for large colon disease. If only hemoglobin is present in the feces, then bleeding from the foregut is more likely. The test has a relatively low sensitivity for colonic disease, which means it may not detect all cases of colonic ulceration.

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 (Jones 2009). This technology may be available in some specialist centers.

Treatment for Colonic Ulceration

Current research indicates that 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 may lead to abnormal patterns of fermentation in the large bowel and to alterations of the intestinal microbiota. Readjusting feeding regimes to better mimic more natural feeding habits (high roughage diets) may go a long way to preventing colonic ulcer formation, and may also help treat low-grade ulceration. This is an area in which more research is required.

Horses with moderate-to-severe colonic ulceration may benefit from the following treatments (Jones, Andrews 2009):

  • Discontinue NSAID medication
    If pain medication is required, consider alternatives such as opioids (butorphanol or fentanyl), lidocaine/lignocaine infusions or epidural anaesthesia.
  • Minimize stress
  • Decrease bulk in the diet in order to give the colon time to heal.
    • Feed frequent small meals at regular intervals (4-6 times daily).
    • Use a pelleted complete feed that is alfalfa (lucerne) based and contains at least 30% dietary fiber.
    • Allow short periods of grazing fresh grass (10-15 minutes, 2-3 times per day) – this is also good for stress minimization.
  • Corn oil, 1 cup given 1-2 times daily. Corn oil helps increase the caloric intake without adding bulk to the diet. Other Omega-3-rich oils can also be used.
  • Psyllium mucilloid, 5 tablespoons given 1-2 times per day. Psyllium mucilloid is an amylase-resistant fermentable fiber that is 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 healing (Jones et al. 2009).
  • Sucralfate may bind to the ulcer bed and act as a protective cover over the ulcer. Once bound, sucralfate can stimulate the release of protective prostaglandins. Sucralfate is known to work for gastric ulceration, however is not clinically proven with colonic ulcers. Sucralfate has very few side effects in horses and is worth considering.
  • Plasma infusions for severe hypoproteinemia and edema.
    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 will benefit colonic healing. Hetastarch is a cheaper alternative than plasma for increasing the plasma oncotic pressure, but Hetastarch will not improve the hypoalbuminemia.
  • Water. Encourage regular water intake to maintain hydrated intestinal contents.

Improvements in clinical signs should be seen within 1-2 weeks, however the colon will take longer to heal – on average 3-4 months, sometimes longer. 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, such as antacids and ranitidine, have not been found to be beneficial in treating colonic ulcers. Proton-pump inhibitors, such as Omeprazole, also have no known effect, as there are no gastric-acid-producing proton pumps in the large colon.

Misoprostal, a synthetic form of prostaglandin E1, theoretically may prevent worsening of clinical signs due to its cytoprotective effect, however this is not clinically proven in horses. The side effects of Misoprostal include abdominal cramping, diarrhea, sweating, and abortion in pregnant mares. Use of Misoprostal may be indicated if the horse has a painful condition that requires continuing NSAID administration (Jones 2009).

In the rare, extreme cases, when 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. Advise clients of the risks of over-administration.

Ensure horses are fed an appropriate diet that constitutes primarily roughage, such as grass, hay and chaff. Carbohydrate-rich supplements such as grain should only be added to the diet as necessary to fulfill energy requirements. Consider beet pulp and Omega-3 rich oils as alternative energy sources to grain.


  • Andrews, F.A. et al. Colonic Ulcers: a pain in the hindgut!
  • Barton, M. (2011) Understanding Abdominal Ultrasonography in Horses. Which Way Is Up. Compendium: Continuing Education for Veterinarians.,
  • Jones, S.L. et al. (2009) Right Dorsal Colitis. In: Current Therapy in Equine Medicine, ed. N.E. Robinson and K.A. Sprayberry. Elsevier pp. 430-432.
  • Pellegrini, F.L. (2005) Results of a large-scale necroscopic study of equine colonic ulcers. Journal of Equine Veterinary Science 25:113-117.

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