Right dorsal colitis: a pain the In hindgut (Proceedings)

Unlike EGUS, colonic ulcers and the condition Right Dorsal Colitis (RDC) occur less frequently, but may lead to hypoproteinemia and more severe clinical signs. In a necroscopic study of 545 horses, 44% of non-performance horses and 65% of the performance horses had colonic ulcers. Colonic ulcers are probably associated with inhibition of prostaglandins by stress induced release of endogenous corticosteroids or the administration of NSAIDs. Early in the condition, horses present with non-specific signs of mild intermittent or recurring colic episodes, lethargy and partial anorexia. However, as the condition worsens clinical signs may include complete anorexia, fever, and diarrhea. Progression of RDC may lead to dehydration, ventral edema, and weight loss. Differential diagnoses for this condition include EGUS, large colon displacement and/or impaction, infectious causes of diarrhea (Salmonellosis, Potomac Horse Fever, Clostridium), granulomatous enteritis, eosinophilic enterocolitis, and intestinal neoplasia.

Diagnosis

A presumptive diagnosis of RDC can be made on history, clinical signs, changes on CBC (mild anemia, toxic changes in PMNs, left shift), hyperfibrinogenemia, hypoalbuminemia, and hypocalcemia. Peritoneal fluid analysis may show a mild increase in WBC count and increase in total protein concentration. In a recent study, a guaiac-based fecal occult blood test was shown to have a good positive predictive value (72%) and a poor negative predictive value (51%) in the diagnosis of RDC.7 In that study many horses that had gastric or colonic ulcers had negative tests (i.e. false negatives). Gastroscopic examination of the stomach if negative may help rule-in RDC in horses showing typical clinical signs, especially if there is concurrent hypoproteinemia. Abdominal ultrasonography of the right dorsal colon may show mural thickening (normal = < 4mm).8 The peripheral wall of the right dorsal colon can be scanned percutaneously through intercostals spaces 11 to 15, ventral to the ventral margin of the right lung field.

Every effort should be made to rule-out infectious causes of diarrhea such as, Salmonellosis and Potomac Horse fever (PHF) in horses with diarrhea. Fecal cultures and PHF serology and PCR can be helpful in ruling-out these conditions. Horses with Salmonellosis will have signs similar to RDC and these diseases may occur together.

Treatment

The principle goals of treatment for RDC includes discontinuing use of NSAIDs, decreasing gut fill to allow the colon to rest, frequent feedings, reducing inflammation, and restoring the normal colon absorptive function. Reduction in gut fill can be accomplished by decreasing or eliminating dry hay from the diet and replacing with frequent feeding of alfalfa-based pelleted complete feeds with at least 30% dietary fiber (Purina Senior™, 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 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. The complete feed diet should be continued for 3 to 4 months or at which time hypoproteinemia and hypoalbuminemia has resolved.

Psyllium mucilloid (Equisyl Advantage™, Animal Health Care Products) or psyllium hydrophilic mucilloid (Metamucil®, Proctor & Gamble, Cincinnati, OH) can be added to the diet to shorten transit time for ingesta and increase water content of the GI tract. Also, psyllium increased the concentration of short-chain fatty acids in the colon of other species which reduces inflammation and thus may reduce inflammation in the horse colon. Furthermore, Corn or Safflower oil (1 cup, added to feed, q12h) can be added to the complete feed to increase Omega-3 fatty acids. Omega-3 fatty acids competitively inhibit the activity of cyclooxygenase enzyme, which is necessary for eicosanoid production. A diet rich in omega-3 fatty acids may reduce the eicosanoid production, thereby decreasing inflammation.

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, sucralfate (22 mg/kg, orally, q6-8h), a sucrose octasulfate and polyaluminum hydroxide complex, has been used for treatment of RDC. This compound has a strong affinity to bind to gastrointestinal mucosa. It has a greater affinity to bind to ulcer craters when compared to intact epithelial cells. In man, sucralfate is more adherent to duodenal ulcers than gastric ulcers despite the duodenal pH > 4.0. Thus, sucralfate may bind to "ulcer craters" in the colon of horses forming a proteinacous bandage. Furthermore, sucralfate, once bound to the ulcer crater, may stimulate local prostaglandin production which may exert 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 trailering 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.8

References (available on request)