LVMA Equine Committee Professor and Director
Equine Health Studies Program
Professor of Equine Medicine
Department of Veterinary Clinical Sciences
School of Veterinary Medicine
Louisiana State University
Baton Rouge, LA 70803
Ulcers in the equine colon (intestine) are common in performance horses and lead to decreased performance, vague clinical signs (partial loss of appetite, rough dull hair coat, intermittent mild colic, and diarrhea), changes in blood work (low protein and high white blood count, and inflammation) and may go undiagnosed for months because horses are usually normal between acute episodes. All ages and breeds of horses are susceptible to ulcers of the colon and current treatment focuses on reducing bulk in the diet, use of gut coating agent and condition agents, mild laxatives, and oils to promote healing.1
Ulcers of the colon are usually referred to as Right Dorsal Colitis (RDC) as most of the ulcers are located in this part of the large intestine, which is in contact with the right body wall. This condition occurs less frequently than gastric ulcers, but might lead to fluid under the skin (edema) and diarrhea. In one study of 545 horses, nearly half (44%) of non-performance had colonic ulcers, whereas 65% of performance horses had colonic ulcers.2 Colonic ulcers are probably associated with stress induced release of the body's natural steroids or the administration of non-steroidal anti-inflammatory agents, like Bute or Banamine. Early in the condition, horses present with non-specific signs of mild intermittent or recurring colic episodes, lethargy and loss of appetite. However, as the condition worsens clinical signs may include complete loss of appetite, fever, colic and diarrhea. Progression of RDC may lead to dehydration, ventral edema, and weight loss. Other conditions that could look like RDC include gastric ulcers, other causes of colic (large colon displacement and/or impaction), infectious causes of diarrhea (Salmonellosis, Potomac Horse Fever, Clostridium), granulomatous and eosinophilic enteritis (inflammatory bowel disease), and intestinal neoplasia (cancer).
A presumptive diagnosis of RDC can be made on history (recurrent colic episodes, intermittent diarrhea, loss of performance, weight loss), clinical signs as mentioned above, changes in blood work (mild anemia, toxic changes in white blood cells, and a high number of white blood cells, low blood proteins and high inflammatory proteins, and low calcium). Peritoneal (belly) fluid analysis might show a mild increase in WBC count and increase in total protein concentration (> 2.5 g/dl). The presence of blood in the manure can be helpful as an ancillary diagnostic test in horses with RDC.2 Recently, a new test (Succeed Fecal Blood Test, Freedom Health, LLC, Aurora, OH) (Figure 1) was commercially developed to measure blood in the manure and this test was shown to be very good at predicting RDC. The positive test might help your veterinarian determine if the horse has RDC, but will be used as a part of a total diagnostic approach.
Figure 1. Succeed® Equine Fecal Blood Test™ showing positive result (TST) for albumin (A) and hemoglobin (H), denoting hemorrhage from the hindgut (colon) in a horse with colonic edema (on ultrasonographic examination) and right dorsal colitis.
Your veterinarian may put an endoscope (gastroscope) in the stomach, to see if the horse has gastric ulcers, because the clinical signs of gastric ulcers are similar to those of RDC. If gastric ulcers are present then your veterinarian may want to start antiulcer treatment to see if the horse gets better. However, sometimes gastric and colonic ulcers can occur in the same horse, especially if there is concurrent changes in the blood work. Treatment with antiulcer medications will have no affect on colonic ulcers.
Another diagnostic your veterinarian may perform is abdominal ultrasound of the right dorsal colon. This technique may show thickening (normal < 0.4 cm) of the colon wall, which lies against the right body wall in the abdominal cavity.3 Your veterinarian will scan the right dorsal colon by placing the probe between the ribs over the colon in the right side of the horse. Examination of the colon might reveal thickening of the colon wall as see in the photos below (Figure 2a and 2b).
If the horse has diarrhea, your veterinarian will make every effort to rule-out infectious causes such as, Salmonellosis and Clostridium, by using fecal cultures. However, these conditions will have similar clinical signs might occur in the same horse.
The principle goals of treatment for RDC includes discontinuing or avoiding the use of NSAIDs (especially Bute and Banamine), decreasing gut fill and bulk in the diet (mechanical load on the colon) to allow the colon to rest, frequent feedings, reducing inflammation, coating and restoring the normal colon absorptive function and implementing methods to decrease stress.1 To reduce gut fill your veterinarian might recommend replacing the dry hay in the diet with an alfalfa-based complete pelleted feed like Equine Senior (Purina SeniorÔ, Purina Mills, St. Louis, MO). This reduces gut fill and decreases the mechanical load on the colon. The horse can be allowed to graze small amounts of fresh grass (10 to 15 minute intervals four to six times daily) to help decrease the stress of stall or dry paddock confinement and maintain body weight. The switch to a complete feed diet should be made over several days to a week to allow the gastrointestinal tract time to acclimatize to the feed change. This dietary change is only temporary and may last up to 3 to 4 months or at which time the blood work returns to normal. Your veterinarian may recommend weekly blood work once the horses diet is switched to the pellets.
Figure 2a. Edema (1.37 cm; yellow box) in the wall of the Right Dorsal Colon in a pony before diet and pharmacologic treatment.
Figure 2b. Right Dorsal Colon in the same pony after 4 weeks of dietary change and treatment with medications. Note that the wall of the Right Dorsal Colon is 0.45 cm (yellow box).
Your veterinarian may recommend psyllium mucilloid (Equisyl AdvantageÔ, Animal Heath Care Products) or psyllium hydrophilic mucilloid (MetamucilÒ, Proctor & Gamble, Cincinnati, OH) added to the diet to lubricate and shorten transit time for feed material and increase water content in the intestines. Also, psyllium increased the concentration of fatty acid in the colon and reduces inflammation.
Furthermore, your veterinarian may suggest the addition of corn or safflower oil (1 cup, added to feed, q12h) added to the complete feed to increase Omega-3 fatty acids. Omega-3 fatty acids effectively block the chemicals released in the body due to stress, which decreases inflammation in the colon due to the ulcers.
The use of medication routinely used for gastric ulcers (antacids, omeprazole, or ranitidine) would not be expected to be effective in treatment of RDC. However, your veterinarian might recommend the use of sucralfate, a sucrose octasulfate and polyaluminum hydroxide complex, that binds to the ulcer bed and forms a bandage over the ulcer. Also, sucralfate, once it has adhered to the ulcer crater, stimulates local protective chemicals called prostaglandins, which has a “cytoprotective” effect on the colon mucosa.
Minimizing physiologic and environmental stresses can also be helpful in controlling RDC. Stall rest, reduction of strenuous exercise or training, and reduction in travel are ways to decrease stress. Horses should always have adequate amounts of clean fresh water and should be provided a mineral/salt mix to ensure adequate water intake. Flavored water can be given to horses at home so that water intake can remain the same on the road and at shows.
Generally it takes between 1 to 2 weeks to see improvement in clinical signs, once the diet has been changed. Weekly monitoring of blood work is important indicators of response to treatment and prognosis. Improvement in blood work might take several weeks. In addition to blood work, your veterinarian will recommend serial ultrasonographic examinations of the Right Dorsal Colon to help in monitoring response to treatment. Typically weekly to every two week ultrasonographic examinations can help your veterinarian gauge therapy. The swelling in the wall of the Right Dorsal Colon should decrease within 4 to 6 week after initiation of dietary changes and treatment (Figure 2b), but may take longer in some horses.
The response to treatment is good, especially if the horses' clinical signs, blood work, and ultrasound signs improve rapidly. Be sure you contact your veterinarian as soon as you recognize these signs as the longer it continues the more difficult it is to treat successfully.