Bit & Bridle

Equine Peritonitis

Other Names

  • Peritoneal inflammation
  • Abdominal cavity infection
  • Inflammation of the peritoneum

What is Peritonitis in Horses?

Peritonitis is an inflammation of the peritoneum — the thin, smooth membrane that lines the inner wall of the abdominal cavity and covers the organs within it. The peritoneum plays a vital role in supporting abdominal organs, producing lubricating fluid, and providing an immune defence within the abdomen. When it becomes inflamed, the consequences can be severe and life-threatening.

In horses, peritonitis may be classified as primary (caused by direct infection of the peritoneum) or, more commonly, secondary (resulting from another abdominal condition that allows bacteria or intestinal contents to contaminate the peritoneal cavity). It may also be localised (contained to one area) or diffuse (spreading across the entire abdominal cavity). Diffuse bacterial peritonitis carries a particularly grave prognosis.

Due to the horse’s sensitive digestive system and the large surface area of the equine peritoneum, even relatively minor contamination can escalate rapidly into a serious systemic illness. Peritonitis requires urgent veterinary attention and is almost always treated as an emergency.

Causes

Peritonitis in horses typically arises as a complication of another condition that disrupts the integrity of the gastrointestinal or reproductive tract:

  • Gastrointestinal rupture: Rupture of a distended stomach (gastric rupture), a devitalised section of intestine, or a colonic torsion can spill intestinal contents — bacteria, ingesta, and digestive enzymes — directly into the peritoneal cavity. This is usually rapidly fatal.
  • Colic complications: Intestinal accidents such as volvulus, intussusception, or strangulating colic can cause bowel ischaemia and bacterial translocation across the gut wall, even without frank rupture.
  • Post-surgical contamination: Abdominal surgery carries a risk of peritonitis through contamination during the procedure or post-operative bowel leakage.
  • Penetrating wounds: Stab wounds, fence injuries, or impalement injuries that breach the abdominal wall can introduce bacteria directly.
  • Uterine rupture or infection: Dystocia, post-foaling tears, or uterine infections (metritis) in mares can lead to peritonitis, particularly if uterine contents contaminate the abdomen.
  • Rectal tears: A serious complication of rectal examination or rectal palpation, particularly if performed by an inexperienced individual. Full-thickness tears allow faecal contamination of the peritoneal cavity.
  • Haematogenous spread: Bacteria carried in the bloodstream (bacteraemia) can seed the peritoneum, though this is a less common cause.
  • Idiopathic: Occasionally, no clear cause is identified.

Symptoms and Signs

The clinical signs of peritonitis in horses vary depending on the cause, severity, and whether the condition is acute or chronic:

  • Acute, severe peritonitis: Signs of shock — rapid heart rate, pale or congested mucous membranes, cold extremities, rapid breathing, profound depression, and collapse. The horse may show signs of extreme pain or, paradoxically, become very quiet and withdrawn.
  • Colic-like signs: Abdominal pain ranging from mild to severe, pawing, rolling, looking at the flanks, and reluctance to move.
  • Elevated temperature: Fever is common unless the horse is in circulatory shock, in which case temperature may drop.
  • Abdominal guarding: The horse may be reluctant to have the abdomen touched or palpated.
  • Reduced gut sounds: Decreased or absent borborygmi (gut sounds) on auscultation due to paralytic ileus.
  • Chronic peritonitis: May present with weight loss, intermittent mild colic, reduced appetite, and a tucked-up appearance over weeks to months — making it more difficult to diagnose.
  • Diarrhoea or absence of faecal output: Depending on the underlying cause and degree of ileus.

Diagnosis

Diagnosis of peritonitis involves a combination of clinical examination and diagnostic tests:

  • Peritoneal (abdominal) fluid analysis (abdominocentesis): A sample of the fluid within the abdominal cavity is collected via a needle through the ventral abdomen. In peritonitis, the fluid is typically cloudy or discoloured, with elevated white cell counts, increased protein, and often bacteria visible on cytology. This is the most important diagnostic test.
  • Blood work: Full blood count typically reveals elevated white cell count (or paradoxically low in severe endotoxaemia), elevated fibrinogen, and changes consistent with systemic inflammatory response.
  • Ultrasound: Transabdominal and transrectal ultrasound can reveal free fluid, thickened bowel, and areas of localised inflammation.
  • Rectal examination: May reveal distended or abnormal intestinal loops, thickened peritoneum, or masses.
  • Nasogastric intubation: To check for gastric reflux and relieve gastric distension in cases with concurrent ileus.

Treatment

Peritonitis requires intensive, urgent treatment. Management strategies include:

  • Broad-spectrum antibiotics: Intravenous antibiotics covering both gram-positive and gram-negative organisms, including anaerobes, are the cornerstone of treatment. Combinations such as penicillin plus gentamicin plus metronidazole are commonly used.
  • Non-steroidal anti-inflammatory drugs (NSAIDs): Flunixin meglumine (Finadyne) is preferred for its anti-endotoxin properties in addition to anti-inflammatory effects. Helps control pain and reduce the systemic effects of endotoxaemia.
  • Intravenous fluid therapy: Essential to combat dehydration, support blood pressure, and address electrolyte imbalances, particularly in horses with concurrent ileus or shock.
  • Peritoneal lavage: In some cases, the abdominal cavity is repeatedly flushed with sterile saline via indwelling drains to physically remove bacteria and inflammatory products. Most practical in acute cases where surgery is not an option or as post-surgical management.
  • Surgery: Exploratory laparotomy may be required to identify and address the source of contamination — bowel resection, uterine removal, wound repair. The decision must be weighed carefully against the horse’s prognosis and condition.
  • Supportive care: Nutritional support (often parenteral or via nasogastric tube), gut motility drugs (e.g., lidocaine infusions), and careful management of systemic complications.

Prevention

  • Manage colic cases promptly — delayed treatment of surgical colic significantly increases the risk of peritonitis.
  • Ensure any rectal examinations are performed by a trained veterinarian using appropriate technique and lubrication.
  • Manage reproductive emergencies (dystocia, retained foetal membranes) promptly and with veterinary oversight.
  • Use experienced surgical teams when abdominal surgery is required, and follow meticulous post-operative monitoring protocols.
  • Inspect fencing and field hazards regularly to minimise penetrating abdominal injuries.
  • Administer tetanus vaccination — though not directly preventive for peritonitis, it protects against one serious consequence of penetrating wounds.

Prognosis

The prognosis for peritonitis in horses depends heavily on the underlying cause and the speed of diagnosis and treatment:

  • Gastric or colonic rupture: Almost universally fatal. Humane euthanasia is generally the only appropriate course of action once rupture is confirmed.
  • Acute bacterial peritonitis without rupture: Prognosis is guarded to poor, but survival is possible with aggressive, early treatment. Reported survival rates vary widely (20–60%) depending on the study and case severity.
  • Post-surgical peritonitis: Prognosis is guarded; outcome depends on the degree of contamination, pathogen involved, and how rapidly it is detected.
  • Chronic/idiopathic peritonitis: Generally a better prognosis than acute septic peritonitis; many cases respond well to prolonged antibiotic therapy.

When to Call the Vet

Peritonitis is a veterinary emergency. Call your vet immediately if your horse shows:

  • Signs of severe abdominal pain or colic that does not respond to initial management
  • Rapid deterioration in condition — increasing heart rate, pale or discoloured gums, cold sweat
  • Known penetrating abdominal wound, even if the horse appears stable
  • A mare that has recently foaled showing signs of pain or systemic illness
  • A horse recovering from colic surgery that develops fever, reduced gut sounds, or signs of pain

Do not delay — peritonitis progresses rapidly and every hour matters. Early intervention dramatically improves the chances of a successful outcome.

Frequently Asked Questions

What is the difference between peritonitis and colic in horses?

Colic is a general term for abdominal pain and can have many causes — most of which are not peritonitis. However, certain types of colic (particularly surgical colic involving bowel displacement or strangulation) can lead to peritonitis if untreated or if bowel leakage occurs. A horse with peritonitis will often show colic-like signs, but typically appears more systemically unwell — with fever, elevated heart rate, and signs of toxaemia — than a horse with simple spasmodic colic.

Can a horse recover fully from peritonitis?

Full recovery is possible, particularly in cases of mild or chronic peritonitis treated early and aggressively. However, many horses that survive acute septic peritonitis develop adhesions — fibrous bands of scar tissue that form between abdominal organs — which can cause ongoing problems including recurrent colic. The likelihood of returning to full athletic work depends on the severity of the original episode and the extent of any adhesion formation.

Is peritonitis in horses contagious?

Peritonitis itself is not contagious — it is not spread between horses. However, if it is caused by a highly contagious underlying infection (such as Salmonella), appropriate biosecurity measures should be observed, as the infection causing the peritonitis may be transmissible. Your vet will advise on any necessary isolation measures.

How quickly can peritonitis develop in a horse?

Acute peritonitis from bowel rupture or major contamination can result in rapid deterioration within hours. A horse that appears to have a routine colic in the morning may be in critical condition by the afternoon if a significant intestinal accident has occurred. This is why any colic that fails to resolve within two hours, or where signs worsen, should be assessed by a vet without delay. Early referral to an equine hospital greatly improves outcomes.