Peritonitis in the Horse
Dr. Melissa Mazan
The peritoneal cavity is a very large space that encloses the abdominal organs. It is covered by a thin tissue layer called the peritoneum. The peritoneum is so thin that it is actually made of only one layer of cells. The peritoneum may seem delicate, but it is part of a critical defense system that protects the abdominal organs. Signs of colic
In addition to covering the abdominal contents, the peritoneum also governs the motion of fluid, proteins, and other molecules from the peritoneal space to the blood vessels. The peritoneum is also extremely important in lubricating the abdominal organs, so that when the horse moves, the internal organs can easily glide past each other.
Peritonitis is the medical term that refers to inflammation of the peritoneum. Peritonitis may be due to both infectious and non-infectious causes. Infectious causes are most common, particularly bacterial contamination from the intestinal tract. Penetrating wounds, ruptured gastric ulcers, migrating intestinal parasites, and foreign bodies can all contribute to the development of peritonitis.
Peritonitis due to ruptured gastric ulcers is most common in foals, and migrating intestinal parasites most commonly do their damage in horses that are not dewormed or are dewormed infrequently. An outbreak of strangles (S. equi) may result in intra-abdominal abscesses in a small number of horses. The majority of cases of peritonitis, however, are unpredictable.
Horses are very sensitive to endotoxin, a by-product of the gram negative bacteria that are the common culprits in peritonitis. Thus, peritonitis, when untreated, can be life-threatening. Survival depends very much on how severe the individual case is. The severity of the peritonitis often depends on the cause. A catastrophic rupture of the intestine usually causes the death of the horse. Microscopic ruptures from gastric ulcers, or penetrating wounds, however, can often be treated.
Horses are prone to forming adhesions (the intestines stick to each other) after peritonitis, so even horses that survive in the short-term can experience long-term difficulties.
What to Watch For
Loss of appetite
High heart rate
Your veterinarian will take a careful medical history and perform a complete physical examination. Based on the results of these, she will usually choose to perform more tests:
Abdominocentesis (sample of the peritoneal fluid)
A rectal examination
CBC and chemistry profile
Broad spectrum antibiotics
Removing the cause
It is important to follow all of your veterinarian's instructions for giving antibiotics. Horses with peritonitis may require weeks or even months of antibiotics. Antibiotic treatment often alleviates the symptoms of peritonitis, such as colic and weight loss, long before the infection itself is completely eradicated.
It is important to follow all of your veterinarian's feeding instructions. Horse with peritonitis may not be able to tolerate a rich diet; other horses who have adhesions may not be able to tolerate a diet with a high fiber content.
It will be important to monitor your horse's appetite and manure output. A horse's appetite may be the single best monitor of his sense of well-being. If your horse has diminished manure output, he may be developing adhesions that are preventing him from moving food and manure through his system.
Most cases of peritonitis are unanticipated and impossible to prevent. It is important to monitor for signs of colic in any outbreak of strangles – this may be the signal that your horse has developed an abdominal abscess.
Foreign body ingestion can be prevented by making sure that your pastures are free of any objects that your horse might want to nibble on – other than hay.