Peritonitis in Horses: Abdominal Infection, Colic, and Fever
- See your vet immediately. Peritonitis is inflammation or infection inside the abdominal cavity and can become life-threatening fast.
- Common signs include fever, depression, reduced appetite, belly pain or colic, decreased manure, and a tucked-up or guarded abdomen.
- Your vet often confirms the problem with an exam, bloodwork, ultrasound, and abdominocentesis (an abdominal fluid sample).
- Treatment usually involves antibiotics, pain control, fluids, and close monitoring. Some horses also need referral hospitalization or surgery if there is a ruptured organ, penetrating wound, or intestinal problem.
- Early treatment improves the outlook. Mild to moderate medical cases may recover well, while septic or surgical cases carry a more guarded prognosis.
What Is Peritonitis in Horses?
Peritonitis is inflammation of the peritoneum, the thin lining that covers the abdominal cavity and many abdominal organs. In horses, this inflammation may be septic (caused by bacteria or contamination) or nonseptic (caused by irritation, inflammation, surgery, trauma, or leakage of irritating material). Either form can make a horse feel very sick very quickly.
Many horses with peritonitis show signs that overlap with colic, including abdominal pain, reduced appetite, and less manure production. Fever is especially important. A horse with colic plus fever raises concern for an infectious or inflammatory process, and peritonitis is one of the conditions your vet may want to rule out.
Peritonitis can happen after a gastrointestinal leak or rupture, a penetrating wound, abdominal surgery, rectal tear, reproductive tract injury, liver disease, or spread of infection from another site. In some horses, no clear source is found. Because the condition can progress to endotoxemia, shock, adhesions, or laminitis, prompt veterinary care matters.
Symptoms of Peritonitis in Horses
- Fever, often over 101.5-102.5 F
- Mild to moderate colic signs, such as pawing, looking at the flank, or lying down more than usual
- Depression, dull attitude, or reluctance to move
- Reduced appetite or complete refusal to eat
- Decreased manure output or signs of ileus
- Tucked-up abdomen, abdominal guarding, or pain when the belly is touched
- Elevated heart rate and breathing rate
- Dehydration, injected gums, or toxic appearance
- Weight loss and intermittent abdominal pain in chronic cases
- Diarrhea or signs related to the underlying cause in some horses
See your vet immediately if your horse has colic with fever, repeated pain episodes, worsening depression, a high heart rate, or very little manure output. Those signs can point to peritonitis, colitis, strangulating intestinal disease, or another emergency.
Some horses show only mild colic at first, then become much sicker over hours. If your horse recently had abdominal surgery, a penetrating wound, foaling complications, a rectal exam injury, or an abdominal procedure and now has fever or belly pain, treat that as urgent.
What Causes Peritonitis in Horses?
Peritonitis develops when the abdominal lining becomes inflamed or contaminated. In horses, important causes include intestinal leakage or rupture, penetrating wounds, abdominal surgery, rectal tears, liver biopsy complications, intraperitoneal injections, and reproductive tract injuries. Mares can also develop abdominal contamination after foaling-related trauma.
Bacteria may enter the abdomen directly, or inflammation may spread from a nearby organ. Common scenarios include bowel compromise from severe colic, abscesses, uterine or reproductive tract damage, and trauma. In other horses, the cause is less obvious and may be called primary peritonitis when no clear source is identified.
Not every case is caused by a catastrophic rupture. Some horses develop more localized or lower-grade inflammation and respond well to medical treatment. Still, because septic peritonitis can deteriorate fast, your vet will usually approach a horse with fever and abdominal pain as an emergency until proven otherwise.
How Is Peritonitis in Horses Diagnosed?
Your vet will start with a full physical exam, including temperature, heart rate, hydration status, gut sounds, and pain level. Bloodwork often helps show inflammation, infection, dehydration, protein loss, or endotoxemia. Ultrasound can reveal free abdominal fluid, fibrin, thickened bowel, abscesses, or other clues about the source.
A key test is abdominocentesis, also called an abdominal tap. This lets your vet collect peritoneal fluid and evaluate its color, protein, cell count, and bacteria. In septic cases, the fluid often looks abnormal and may have low glucose compared with blood. Cytology and culture can help identify infection, although treatment may begin before culture results return.
Depending on the case, your vet may also recommend rectal examination, nasogastric intubation, lactate testing, repeat abdominal fluid sampling, or referral for advanced imaging and intensive monitoring. Diagnosis is not only about confirming peritonitis. It is also about finding the underlying cause, because that strongly affects treatment options and prognosis.
Treatment Options for Peritonitis in Horses
Spectrum of Care means you have options. Here are treatment tiers at different price points.
Budget-Conscious Care
- Urgent farm call or clinic exam
- Basic bloodwork and abdominal ultrasound when available
- Abdominocentesis if feasible
- Broad-spectrum antibiotics selected by your vet
- NSAID pain control and anti-endotoxin support
- Oral or limited IV fluids, close recheck plan, and strict monitoring
Recommended Standard Treatment
- Hospitalization or day-stay monitoring
- CBC, chemistry, fibrinogen or inflammatory markers, and repeat bloodwork
- Abdominal ultrasound and abdominocentesis with cytology and culture
- IV fluids, broad-spectrum IV antibiotics, and pain control
- Anti-endotoxin care, laminitis monitoring, and nutritional support
- Repeat exams and serial abdominal fluid or ultrasound checks
Advanced / Critical Care
- Referral hospital intensive care
- Continuous IV fluids, plasma or colloid support when indicated, and advanced monitoring
- Serial ultrasound, repeated abdominocentesis, blood gas or lactate testing, and culture-guided antibiotic adjustments
- Management of endotoxemia, ileus, shock, or laminitis risk
- Exploratory surgery if there is suspected rupture, foreign body, devitalized bowel, abscess requiring intervention, or another surgical source
- Extended hospitalization and aftercare planning
Cost estimates as of 2026-03. Actual costs vary by location, clinic, and individual case.
Questions to Ask Your Vet About Peritonitis in Horses
Bring these questions to your vet appointment to get the most out of your visit.
- Do my horse's signs suggest septic peritonitis, nonseptic inflammation, or another cause of colic and fever?
- What did the abdominal fluid sample show, and does it suggest infection or leakage from the intestine?
- Which tests are most important today, and which ones can wait if we need to manage the cost range carefully?
- Does my horse need hospitalization now, or is monitored treatment at home a reasonable option?
- What complications are you most worried about, such as endotoxemia, laminitis, adhesions, or ileus?
- Which antibiotics and pain-control medications are you recommending, and what side effects should I watch for?
- At what point would referral or surgery become the safer option for my horse?
- What signs at home mean I should call you back immediately?
How to Prevent Peritonitis in Horses
Not every case can be prevented, but good management lowers risk. Prompt treatment of colic, penetrating wounds, foaling injuries, fever, and abdominal pain matters. Horses that have had abdominal surgery or invasive procedures need careful aftercare and close monitoring for fever, depression, reduced appetite, or worsening pain.
Work with your vet on safe procedure technique and follow-up care after castration, abdominal taps, reproductive procedures, rectal exams, or surgery. Clean wound care, early attention to drainage or swelling, and fast rechecks when a horse seems "off" can help catch complications before they become severe.
General wellness also helps. Keep vaccinations, parasite control, dental care, and nutrition current so your horse is in the best condition possible if illness occurs. Most importantly, have an emergency plan. Know who to call, where the nearest equine hospital is, and how you would transport your horse if colic and fever develop together.