Bit & Bridle

Equine Ulcerative Colitis

Other Names

  • Ulcerative colitis in horses
  • Equine large intestinal ulceration
  • Inflammatory bowel disease (IBD) of the large colon

What is Equine Ulcerative Colitis?

Equine ulcerative colitis is an inflammatory condition of the large intestine characterised by the formation of ulcers in the mucosal lining — the inner surface of the colon. Unlike equine gastric ulcer syndrome (EGUS), which affects the stomach, ulcerative colitis targets the large colon and, in some cases, the caecum and small colon. The condition disrupts normal colonic function, impairing fluid and electrolyte absorption and leading to diarrhoea, protein loss, and systemic illness.

Ulcerative colitis in horses is less well characterised than gastric ulceration and can be challenging to diagnose without specialist investigation. It can occur as a primary condition or secondary to other disease processes. When significant colonic inflammation is present alongside protein-losing enteropathy, the clinical consequences can be severe.

Related conditions affecting the gastrointestinal tract include equine gastric ulcer syndrome and equine colitis X, both of which may share some clinical features.

Causes

The causes of equine ulcerative colitis are varied and in some cases multifactorial:

  • Non-steroidal anti-inflammatory drugs (NSAIDs): Prolonged or high-dose use of phenylbutazone (“bute”) and other NSAIDs is one of the best-documented causes of large intestinal ulceration in horses. NSAIDs inhibit prostaglandin synthesis, which is important for maintaining the integrity of the intestinal mucosa.
  • Infectious agents: Salmonella spp., Clostridium difficile, and Neorickettsia risticii (the cause of Potomac horse fever) can all induce colonic inflammation and ulceration.
  • Inflammatory bowel disease: Idiopathic inflammatory conditions of the equine intestine, including eosinophilic, granulomatous, and lymphocytic-plasmacytic enterocolitis, may involve the large intestine.
  • Right dorsal colitis: A specific form of NSAID-induced ulceration affecting the right dorsal colon, this is a well-recognised entity in horses on chronic phenylbutazone therapy.
  • Dietary factors: Sudden changes in diet, high-starch feeding, and inadequate roughage may compromise the colonic environment and predispose to mucosal damage.
  • Stress: Transportation, competition, illness, and changes in routine can alter gut motility and microbial populations, potentially contributing to mucosal vulnerability.

Symptoms and Signs

  • Diarrhoea: Ranging from loose, cowpat-like faeces to watery diarrhoea. May be intermittent or chronic.
  • Weight loss: Resulting from protein-losing enteropathy and malabsorption
  • Ventral oedema: Fluid accumulation under the belly and in the lower limbs due to hypoproteinaemia (low blood protein)
  • Lethargy and reduced performance
  • Colic: Variable in severity; some horses show intermittent abdominal discomfort
  • Reduced appetite
  • Fever: When an infectious component is present
  • Poor body condition despite apparently adequate feeding

Diagnosis

Diagnosis of equine ulcerative colitis requires a systematic approach to exclude other causes of diarrhoea and protein loss:

  • Clinical examination: Vital signs, assessment of gut sounds, palpation for colic pain, and evaluation of mucous membranes and hydration status
  • Haematology and biochemistry: Low serum albumin and total protein levels are a hallmark. Elevated white cell count may indicate infection. Faecal culture and PCR testing can identify Salmonella, Clostridium, or Neorickettsia.
  • Abdominal ultrasound: Thickening of the colonic wall, free peritoneal fluid, and changes in wall layering are characteristic findings
  • Rectal examination: Palpation per rectum allows assessment of the pelvic flexure and small colon for wall thickening or abnormal content
  • Colonoscopy: Endoscopic examination of the rectum and small colon can identify mucosal ulceration, though access to the full large colon is limited without specialist equipment
  • Intestinal biopsy: Definitive diagnosis of inflammatory bowel disease or specific mucosal pathology requires histopathological examination of tissue obtained by rectal biopsy or, less commonly, laparoscopy
  • NSAID history: A detailed drug history is essential — right dorsal colitis should always be considered in horses on chronic NSAID therapy

Treatment

Treatment depends on the underlying cause and severity:

  • Remove the cause: Immediate cessation of NSAIDs in cases of NSAID-induced colitis. Treat any identified infection appropriately.
  • Nutritional support: High-quality hay, reduced concentrate feeding, and in severe cases enteral or parenteral nutritional support. For right dorsal colitis, a low-starch, high-fibre diet using alfalfa hay and oil is frequently recommended.
  • Colonic mucosal protectants: Sucralfate is widely used to coat and protect ulcerated mucosal surfaces. Misoprostol (a prostaglandin analogue) may be used to promote mucosal healing in NSAID-induced cases.
  • Corticosteroids: Used in cases of idiopathic inflammatory bowel disease to suppress the immune-mediated inflammatory response. Prednisolone or dexamethasone may be used under veterinary supervision.
  • Intravenous fluids and colloids: Essential for horses with severe dehydration, electrolyte imbalances, or critically low albumin levels
  • Plasma transfusion: In horses with severe hypoproteinaemia, commercial equine plasma or fresh frozen plasma is used to increase colloid osmotic pressure and support recovery
  • Probiotics and prebiotics: May help restore a healthy gut microbiome, though evidence in horses is still emerging

Prevention

  • Use NSAIDs at the lowest effective dose for the shortest necessary duration
  • Avoid chronic NSAID use in horses without regular monitoring — a horse on long-term phenylbutazone should have periodic blood work and ideally abdominal ultrasound
  • Maintain consistent feeding — avoid sudden diet changes
  • Provide adequate fibre and forage as the foundation of the diet
  • Implement good hygiene and biosecurity to reduce the risk of infectious colitis
  • Minimise unnecessary stress around feeding, transport, and competition

Prognosis

Prognosis depends on the underlying cause and the degree of intestinal damage. Horses with NSAID-induced right dorsal colitis that are identified early and managed aggressively have a reasonable chance of recovery, though some develop permanent scarring leading to colonic stricture. Cases caused by infectious agents often resolve with appropriate treatment and supportive care. Idiopathic inflammatory bowel disease carries a more variable prognosis — some horses are well controlled with ongoing treatment, while others deteriorate progressively.

When to Call the Vet

  • Any horse with acute or ongoing diarrhoea — particularly if associated with weight loss, colic, or fever
  • Visible oedema (fluid swelling) under the belly or in the lower limbs
  • A horse on long-term NSAID therapy that develops loose faeces, weight loss, or reduced appetite
  • Any horse that is losing condition despite apparently adequate nutrition

Frequently Asked Questions

Is equine ulcerative colitis the same as right dorsal colitis?

Right dorsal colitis is a specific form of equine colonic ulceration caused by NSAID use, affecting the right dorsal segment of the large colon. Equine ulcerative colitis is a broader term encompassing ulcerative inflammation of any part of the large intestine from various causes. Right dorsal colitis is one subtype of equine ulcerative colitis, and it is one of the most important to recognise given that NSAIDs are routinely used in equine medicine.

Can horses with ulcerative colitis be managed long term?

Yes, many horses can be successfully managed long term with the right combination of dietary modification, appropriate medication, and regular monitoring. Horses with idiopathic inflammatory bowel disease may require ongoing corticosteroid therapy, while those with NSAID-induced colitis that are removed from the offending drug and supported through the healing process often return to normal function.

What is the link between stress and colitis in horses?

Stress alters the normal function of the gut in multiple ways: it changes gut motility, affects the balance of intestinal bacteria (the microbiome), and can compromise mucosal barrier function. Horses that are frequently transported, housed in changing environments, or subjected to intense competition schedules may be at increased risk of intestinal inflammation. Managing stress as part of the overall management plan is therefore worthwhile.

How is equine colitis different from colic?

Colic is a general term for abdominal pain in horses, which can arise from many causes. Equine ulcerative colitis is a specific disease of the large intestinal wall. While colitis frequently causes some degree of colic (abdominal discomfort), it also typically causes diarrhoea and systemic illness — distinguishing it from most simple colic presentations. A horse with chronic diarrhoea and occasional colic signs warrants colitis investigation rather than a routine colic workup. See equine gastric ulcer syndrome for comparison with gastric disease.