Equine colitis

Colitis in horses is a very challenging condition that involves inflammation of the large intestine (cecum and colon). It is seen in both mature horses as well as foals, and can be serious enough for horses to require intensive treatment at an equine hospital.

What causes colitis?

There are a number of different possible causes of equine colitis, which can be either infectious or non-infectious. These include:

Infectious causes

• Bacteria e.g. Salmonella
• Viruses e.g. equine coronavirus
• Parasites e.g. strongyles (small red worms). For more on worming, see here.

Non-infectious causes

• Antibiotic-associated diarrhoea
• Sand impaction (the horse accidentally eating sand, which becomes impacted in their large colon)
• Dietary imbalances/sudden feed changes
• Tumours
• Inflammatory bowel disease
• Eating poisonous plants
• The use of non-steroidal anti-inflammatory drugs (NSAIDs), such as Bute or Finadyne, can lead to a specific form of colitis termed ‘right dorsal colitis’.

As colitis develops, the inflamed wall of the colon secretes large amounts of fluid and proteins from the body and reduces absorption of water, nutrients and electrolytes (salts and minerals). The intestinal wall also becomes permeable to bacteria and their toxins, which may gain access to the bloodstream and cause a syndrome termed endotoxaemia (bacterial toxins in the blood). This can affect various organs, so colitis is a disease that is not just limited to the large intestine, but can affect the entire body.

Common clinical signs of equine colitis

The main symptom of equine colitis is diarrhoea, which can range in consistency from watery to cowpat. It will often have a foul smell and can sometimes contain blood. In some cases, faeces can be normal but other signs are present, such as colic (decreased appetite, rolling, kicking at the belly, stretching out or flank watching).

Affected horses are often lethargic, have a high temperature, have no or a reduced appetite, and aren’t keen to exercise. If diarrhoea is severe, and the horse has lost large volumes of fluids, dehydration can develop. Signs of dehydration include:

• Sticky gums
• Prolonged skin pinch test
• Cold ears and lower legs
• Weak pulse

When horses lose a lot of protein, they can suffer from swelling of the abdomen and puffy lower limbs. Protein loss can also cause ‘internal oedema’, a thickening of the intestinal wall due to fluid accumulation that is visible on ultrasound imaging.

Additionally, signs of endotoxaemia can occur, including:

• Increased heart rate
• Increased respiratory rate
• Reddened gums with a thin purple line above the teeth
• Decreased blood flow to body tissues

Horses can be affected in varying degrees, but most horses appear very unwell.

How to diagnose colitis

Diagnosis of equine colitis is usually made based on the horse’s clinical signs and the results of blood tests.

To determine the cause of colitis, a faecal sample is tested for bacteria, viruses and parasites, and blood tests can also be helpful. However, in around 50% of cases, a cause is never identified.

As well as attempting to detect the cause of the illness, blood tests can also assess the severity of disease and help in determining a treatment plan. Abdominal ultrasound can be used to evaluate the thickness and motility of intestinal organs, and identify ‘right dorsal colitis’.

Your vet may also perform: 

• A rectal examination
• X-rays
• Assessment of the abdominal fluid collected through a belly tap

Ways to treat equine colitis

Although colitis in horses can be caused by many things, the treatment for the disease is mostly the same. Affected horses are often taken to an equine hospital in order to receive intravenous fluids to enable rehydration as well as replace electrolytes.

If protein loss and endotoxaemia are severe, horses may undergo a plasma transfusion. If bacteria is present in other organs, antibiotic therapy is given, and anti-inflammatory and pain medication may also be administered.

In cases of endotoxaemia, an anti-endotoxic agent is given, and oral medicines that absorb disease-causing bacteria are occasionally administered, alongside probiotics, to promote the good bacteria in the body.

Endotoxaemic horses are also at risk of developing laminitis, so vets may use ice boots to prevent this.

Clinical signs are closely monitored, and a physical examination is often repeated, with various blood tests undertaken frequently to adjust therapy.

Some causes of colitis can be passed between horses and some bacteria can also be transmitted to humans. Therefore, horses with colitis are always isolated to prevent transmission. It is important to follow the vet’s biosecurity instructions for the entire barn to prevent the spread of disease.

When to call the vet

In all but the mildest cases of diarrhoea in your horse, it is best to call your vet. The prognosis of equine colitis depends on the severity of disease and response to therapy within the first two to three days. So the sooner your vet can diagnose colitis and begin treatment, the better.