Peritonitis — what it is and how to treat it [H&H VIP]

  • Colic in horses and peritonitis are closely linked. One condition can soon lead to the other and both need to be taken seriously.

    A quick review of the abdominal area reveals many reasons why horses are vulnerable to abdominal pain — particularly colic, but also peritonitis. When we consider some modern management methods, the equine abdomen could be considered an accident waiting to happen.

    The stomach of an average sized horse has a capacity of between 5-15l. This would be adequate for his natural grazing habits, but it’s relatively small for an animal confined to a stable and eating irregularly rather than continuously. Certainly, stabled horses fed concentrates are more likely to develop colic than those out at grass.

    Next, consider that the thoroughbred-type horse will have more than 22m of small intestine and 4m of large bowel (colon) crammed inside his abdominal cavity. None of this lengthy bowel is securely attached, so there is a risk that it may become twisted and tangled.

    Horses are hindgut fermenters. This means most of their high-fibre food is digested at the rear end of the guts, causing another digestive challenge.

    And there’s yet further potential for problems if parasitic worms attack the intestines.

    Nature’s cling film

    Peritonitis means inflammation of the peritoneum, a thin membrane layer within the abdomen. The peritoneum is a little like nature’s equivalent of cling film, lining the abdominal cavity and acting as a protective covering for almost all of the abdominal contents.

    Not only does the peritoneum act as a protective wrapping, but it also secretes a protective substance called serous fluid. Serous fluid helps lubricate the abdominal contents and has antibacterial properties. This produces a healthy surface for the gut, so the various structures slide smoothly over one another.

    Peritonitis occurs when the normally smooth peritoneal surfaces become inflamed, resulting in soreness and irritation.

    Lowered defences

    To understand the signs of peritonitis, it is important to understand the causes.

    Frequently, peritonitis is thought of as some kind of abdominal infection. In many cases, bacteria are involved, but there has to be some reason why they are multiplying in the wrong place inside the abdomen.

    There are many possible underlying causes, such as trauma — for example a nasty stake wound that penetrates the abdomen — or some kind of foaling or breeding accident. People often imagine that a horse might have eaten something sharp that has perforated the bowel, but this is rare.

    Much more common is that the gut is diseased and the natural defences impaired, resulting in a leaky gut that allows bacteria to seep through. It is also possible for horses to develop peritonitis as a result of a tumour or because of a parasite infection.

    The precise cause is often unidentified. In different studies, no definitive diagnosis was found in somewhere between 15-50% of cases. So vets can tell that peritonititis has happened — but not why.

    Violent signs

    When compared with other animals, horses seem to have a low pain threshold for the infl ammation and irritation that is peritonitis. A horse may be rolling around and showing violent signs of colic pain, whereas a cow would just look mildly uncomfortable.

    The signs (see box, below) vary depending on the nature and severity of the condition.

    A localised peritonitis affecting a small area of the abdomen may grumble on for a long time and can be hard to identify.

    On the other hand, a sudden (peracute) episode with a ruptured bowel can present with extremely severe signs of shock, accompanied by sweating and a very painful abdomen. The horse may be unwilling to move at all and such cases will rapidly collapse or may sadly even be found dead.

    Taking a sample

    It is possible to confirm peritonitis in most cases simply by examining a peritoneal fluid sample.

    Your vet will need to perform a relatively straightforward clinical test, commonly known as a “belly tap” or, more properly, abdominocentesis. This test involves collecting a small sample of peritoneal fluid from the horse’s abdomen. Sometimes the fluid is not readily forthcoming, but an ultrasound scanner can be used to help find a pocket of fluid to sample.

    A few drops of fluid can be sufficient to provide the vet with almost all the answers. Just looking at the colour of the fluid is helpful. The normal colour is rather similar to white wine, but if it resembles red wine or, even worse, custard, then it is time to worry.

    In cases of peritonitis, a cloudy fluid that appears more solid and custard-like means that there are pus cells involved. A red colour means bleeding, inflammation and possible bowel damage.

    If there is a ruptured bowel, the peritoneal fluid will be a cloudy green/brown due to the gut contents floating free within the abdomen. This is a catastrophic event and the sooner it is discovered, the sooner something can be done about it.

    More detailed information can be obtained using lab tests to check the type and numbers of cells present and to measure the protein content, as well as check for infection.

    Repeated peritoneal taps are an effective way of monitoring progress in peritonitis cases.

    Treatment options

    Treatment options vary depending on the severity of the condition and the underlying cause, if it is known.

    Early, aggressive treatment is necessary, if it is going to be of benefit. But medical treatment is not the only option open to vets and owners.

    Opening the abdomen may permit any abdominal contamination to be identified — perhaps an area of diseased bowel can be removed, for instance. Surgery is a relatively major procedure, however, and is generally reserved for cases that fail to improve with medical therapy or for horses with worsening abdominal pain.

    Laparoscopy, using small telescope-like instruments, can be an alternative approach to look inside the abdomen in the conscious standing horse, but it does not permit the whole abdomen to be fully examined.

    Another therapy option is abdominal drainage and lavage, where a tube is inserted into the abdomen and sterile fluid is fl ushed in and out. The size of a horse and the limited access to many parts of the abdomen, however, mean that this is not always the ideal solution.

    There are several scientific vet studies on the survival rate, which ranges from 53-86% depending on a multitude of variable factors. These various studies all agree that speed is of the essence.

    Prompt veterinary attention, early diagnosis and proper, effective treatment will increase the horse’s chance of recovery from peritonitis

    Annie’s abdominal problems

    Annie, a 6-year-old riding horse, contracted strangles. After the respiratory signs resolved, she remained dull and depressed. She then started to lose weight and developed mild signs of colic, much to her owner’s consternation.

    The vet’s clinical examination included a peritoneal tap, which confirmed peritonitis as the cause. It was thought the condition was due to an internal abdominal abscess causing strangles complications.

    Annie was admitted to hospital and underwent laparoscopy. The abscess was identified within the abdominal mesentery, which is a double layer of the protective peritoneum. It was carefully drained at surgery and a catheter was inserted to flush out (lavage) the residual infection.

    Annie then received a prolonged course of antimicrobial injections. It was a challenge to effectively lavage through the catheter without allowing leakage into the abdomen or under the skin. The mare and the vets were happier when the tube could at last be pulled out and all were delighted when Annie made a full recovery.

    Is it peritonitis?

    Recognising peritonitis can be tricky. Colic (that is, abdominal pain) can be the most obvious sign of peritonitis, but colic can also have many alternative causes. Other signs of peritonitis can include:

    • A raised heart rate and a fast pulse
    • Fever — a raised temperature
    • Weight loss
    • Loss of appetite
    • Diarrhoea

    Always call your vet if you have any concerns about your horse.

    This article was first published in the 15 May issue of Horse & Hound magazine