Treating hindgut ulcers in horses centers on removing the cause (usually anti-inflammatory drugs), resting the colon with a modified diet, and supporting mucosal healing over weeks to months. Unlike gastric ulcers, which respond well to acid-suppressing medications, hindgut ulcers sit in the large colon where the environment is entirely different, and no single drug reliably fixes them. Recovery depends heavily on dietary management and patience.
What Causes Hindgut Ulcers
The most common form of hindgut ulceration in horses is right dorsal colitis, an inflammatory condition localized to the right dorsal colon. It is strongly linked to the use of NSAIDs, particularly phenylbutazone (“bute”) and flunixin meglumine (“Banamine”). These drugs block an enzyme called COX-1, which normally produces protective compounds that maintain blood flow and mucus production in the colon wall. Without that protection, the tissue becomes vulnerable to damage.
The right dorsal colon is especially at risk because of its anatomy. The lumen narrows where it meets the transverse colon, slowing the passage of digested material. Phenylbutazone binds to roughage in the gut and gets released during fermentation, so it sits in prolonged contact with the colon wall at this bottleneck. Research from the American Journal of Veterinary Research found that phenylbutazone at standard doses can trigger adverse gastrointestinal effects in as few as three days. At moderate to high doses given twice daily, some horses developed acute necrotizing enterocolitis within seven to ten days. Horses that are dehydrated, fighting an infection, or already have compromised gut lining face significantly higher risk.
Recognizing the Signs
Hindgut ulcers don’t always announce themselves dramatically. Common signs include recurring mild colic, poor appetite, weight loss, a dull coat, loose manure or intermittent diarrhea, and sensitivity when pressure is applied to the flank area. Because the damaged colon wall leaks protein, horses with right dorsal colitis often develop low blood protein levels (hypoproteinemia), which can cause ventral edema, the puffy swelling along the belly and sheath or udder.
These symptoms overlap with many other conditions, which makes diagnosis tricky. Your veterinarian may use abdominal ultrasound to measure the thickness of the right dorsal colon wall. In healthy horses, that wall measures roughly 2.7 to 3.7 millimeters. Significant thickening beyond that range, combined with clinical signs and a history of NSAID use, points strongly toward right dorsal colitis. Fecal blood tests that detect albumin and hemoglobin can also support a diagnosis. These stall-side tests provide results within 15 minutes and show high sensitivity and specificity for detecting blood and protein leaking into the manure.
Stop the Damage First
The single most important step is discontinuing NSAIDs immediately. If your horse needs pain management for another condition, your veterinarian will look for alternatives that are less toxic to the colon. COX-2 selective options carry a lower risk of gut damage than phenylbutazone, though no NSAID is completely safe for a horse with active colonic ulceration.
If NSAIDs were given because your horse was dealing with a musculoskeletal injury or post-surgical pain, work with your vet to develop a pain management plan that doesn’t rely on bute. This might include topical treatments, joint injections, or non-pharmaceutical approaches like controlled exercise and cold therapy.
Dietary Management for Colonic Healing
Diet is the backbone of hindgut ulcer treatment. The goal is to reduce the mechanical workload on the damaged colon while still meeting your horse’s nutritional needs. This means shifting away from long-stem hay and grain toward feeds that are easier to digest and pass through the gut more quickly.
Alfalfa pellets or chopped alfalfa hay are preferred over grass hay during recovery. Alfalfa is more digestible, higher in protein (which helps replace what’s being lost through the damaged colon wall), and its smaller particle size allows faster passage through the large intestine, reducing contact time with ulcerated tissue. Pelleted commercial feeds work similarly. After experimental colon resections in horses, alfalfa-based rations produced better outcomes than straight grass hay.
Grain should be eliminated entirely for at least 10 to 14 days, and ideally longer. Starch that escapes digestion in the small intestine ferments rapidly in the hindgut, producing gas and volatile fatty acids that can further irritate damaged tissue and disrupt the microbial population. When you do reintroduce concentrates, use low-starch, high-fat, and high-fiber options, and introduce them gradually.
Adding corn oil to the diet offers a specific protective benefit. Corn oil is roughly 60% linoleic acid, and supplementation has been shown to decrease acid output while increasing production of prostaglandin E2, a compound that strengthens mucosal defenses. A daily dose of 45 milliliters (about 3 tablespoons) mixed into feed is a reasonable starting point, though some veterinarians recommend higher volumes for horses in active recovery. It’s inexpensive and easy to administer.
Medications Used in Treatment
Your veterinarian may prescribe misoprostol, a synthetic prostaglandin that replaces the protective compounds lost when COX-1 was suppressed by NSAIDs. It directly supports mucosal blood flow and mucus production in the colon. Misoprostol is typically given orally multiple times per day and is the most commonly referenced medication in the veterinary literature for right dorsal colitis specifically. It can cause mild, transient diarrhea or abdominal discomfort when first started.
Sucralfate is another option, usually given orally three times daily. It forms a paste-like barrier over ulcerated tissue, shielding it from digestive acids and bacteria. While sucralfate is well-established for gastric ulcers, its effectiveness in the hindgut is less clear since it may not survive transit through the stomach and small intestine in sufficient concentrations. Still, many veterinarians include it as part of a multi-pronged approach.
Omeprazole (commonly sold as GastroGard) is the standard treatment for gastric ulcers, but it targets stomach acid production and has no direct effect on the colon. If your horse has both gastric and hindgut ulcers, omeprazole addresses only the stomach component.
Supporting Gut Health During Recovery
Psyllium husk supplementation shows promise as a supportive therapy. Beyond its traditional role in clearing sand from the gut, psyllium has anti-inflammatory properties in the intestinal tract and stimulates gut motility. Research in horses found that psyllium supplementation increased microbial diversity in the hindgut, a marker associated with better overall gut health. It also boosted production of a bacterial antioxidant that may help protect the intestinal lining. Psyllium is widely available, affordable, and easy to add to a daily feeding routine.
Probiotics, including the yeast Saccharomyces boulardii, are frequently marketed for equine gut health. While S. boulardii has been shown to survive in the equine gastrointestinal tract, a clinical study in horses with antibiotic-induced diarrhea found no statistically significant difference in recovery time, appetite, or survival compared to untreated horses. Probiotics are unlikely to cause harm, but the evidence for a meaningful clinical benefit in hindgut ulcers specifically is limited.
Timeline and What to Expect
Hindgut ulcers heal slowly. Most horses need two to four months of dietary management and medical treatment before the colon wall returns to a normal thickness on ultrasound. Clinical improvement, including firmer manure, better appetite, and weight gain, often appears within the first few weeks, but that doesn’t mean the tissue is fully healed. Ending treatment too early is a common mistake that leads to relapse.
Your veterinarian will likely recommend follow-up ultrasound exams every four to six weeks to track colon wall thickness and decide when it’s safe to transition back to a normal diet. Reintroduce long-stem hay gradually, starting with small amounts mixed into the pelleted ration, and monitor for any return of symptoms.
Preventing Recurrence
Once a horse has had right dorsal colitis, the colon wall may remain more vulnerable to future damage. The most effective prevention strategy is strict NSAID discipline. Use the lowest effective dose for the shortest possible duration, never exceed recommended dosing, and avoid giving bute to horses that are dehydrated, off feed, or running a fever. These conditions impair blood flow to the gut and dramatically increase the risk of ulceration.
Maintaining a forage-first diet with minimal starch supports long-term hindgut stability. Keeping corn oil as a permanent part of the ration provides ongoing mucosal protection at minimal cost. If your horse requires repeated NSAID courses for a chronic condition, discuss alternatives or protective co-therapies with your veterinarian before starting each course rather than waiting for symptoms to reappear.