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Veterinary surgeon

Sally Hodgson

XLEquine practice

Hook Norton

Veterinary Group


What is peritonitis?

The peritoneum is the thin membrane that

lines the abdominal cavity. Its job is to

secrete the small volume of peritoneal fluid

that lubricates the abdomen. The term

‘peritonitis’ means inflammation of the

peritoneum. The cause may be mechanical,

chemical or infectious. Mechanical causes

include trauma, breeding or foaling

accidents and abdominal surgery. Chemical

peritonitis arises from irritation from leaking

body fluids such as urine, lymphatic fluid,

blood, pus or gut contents, and from drugs

administered into the peritoneal cavity.

Leakage of urine from a ruptured bladder

or abnormalities of the lymphatic drainage

from the intestines (lymphangiectasia) are

seen almost exclusively in very young foals

(Figure 1)


Secondary bacterial infection usually

accompanies mechanical or chemical

causes. Other causes of infectious peritonitis

include abscesses within the abdomen,

parasite migration and some viral infections.

Clinical signs

Symptoms of peritonitis include colic,

dullness and inappetance. The abdominal

wall is often tensed or ‘guarded’ and is

painful to external palpation. The horse may

be reluctant to move. Examination by a vet

will usually find decreased gut motility,

dehydration and fever. Chronic cases may

show weight loss, ventral oedema and

exercise intolerance. Some will have

excessive amounts of peritoneal fluid, which

causes the abdomen to swell up and makes

the horse look bloated. Peritonitis can be

confirmed or ruled out by taking a sample

of peritoneal fluid through the body wall

with a needle, a procedure called a

peritoneal tap or ’belly tap’. The peritoneal

fluid can then be examined to determine the

types and numbers of cells present and the

protein levels. This information helps the vet

to determine whether or not peritonitis is

present, and in some cases can help identify

the cause.

Normal peritoneal fluid is clear and

straw-coloured. Cloudy or dark/red

peritoneal fluid is abnormal. It is also very

useful to send a sample for culture and

sensitivity testing. This identifies the type

of bacteria involved and checks which

antibiotics should treat them and which

they are resistant to.


Pain relief and intravenous antibiotics (most

commonly penicillin, gentamicin and

metronidazole) are essential for the treatment

of septic peritonitis. Antibiotic treatment must

be started straight away, and may need to

be altered depending on the results of culture

and sensitivity testing of the peritoneal fluid

sample. Peritonitis caused by abdominal

abscesses need antibiotic treatment for

weeks to months depending on the types of

bacteria involved. Aggressive intravenous

fluid therapy may be needed to correct

dehydration. Abdominal drainage and

lavage can help to remove bacteria and

toxins from the abdominal cavity in severe

septic peritonitis.

(Figure 2)


Figure 1: Lymphangiectasia

Figure 2: Abdominal drain/tapped



The prognosis varies depending

on the cause. If the primary cause

(e.g. ruptured bladder) can be

identified and corrected, the

prognosis for survival is reasonably

good, however survival in horses with

septic peritonitis after abdominal

surgery is less than 50%. If there is a

gastrointestinal rupture the prognosis

is very grave indeed.

Sally Hodgson VetMB BA BSc MRCVS,

Hook Norton Veterinary Group


in horses