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One simple and accurate description of colic is “severe griping pain in the belly”. This means that what we recognise as equine colic – a horse in obvious pain, restless, often on the ground rolling – is the symptom, not the disease. Colic can be caused by a number of underlying conditions.


Some of the signs of a horse with colic include discomfort and appearing unsettled, pawing the ground, looking back at the flanks and kicking at the abdomen. If the pain is severe enough, the horse will go down and begin to roll in an effort to ease the pain. A horse in this state is distressing to watch and indicates it’s time to immediately ring our hospital to speak with a vet.

Colic can be fatal – the sooner your horse is assessed and treatment begun the better the outcome.

Causes of colic

Colic can be transient and pass quickly or continue to worsen indicating a serious underlying problem. Some of these causes are listed below.

1. Stress

Some horses are more excitable and vulnerable to stress than others. They may react to thunderstorms, or very windy weather – often developing a gut ache in the process. We call this spasmodic colic – the pain can be intense but is responsive to pain relief medication and the colic episode is usually short-lived following treatment.

2. Nutrition

Horses are notoriously sensitive to even the most simple changes in diet. Different foodstuffs can cause intestinal movements to increase and the intestinal muscles to contract painfully. This sort of spasmodic colic usually responds well to veterinary intervention and careful management of the horse’s diet. Or a flatulent colic can result when large amounts of lush green pastures or mouldy hay cause excessive gas production.

Impaction colic results from horses eating too much sand or dirt with their food – often seen in times of drought – or if a horse eats dry straw bedding. This type of colic can take a number of treatments to move the impaction and get the gut back to normal.

3. Gastrointestinal parasites

Bloodworms (strongyles) are the most dangerous of equine internal parasites. They are suspected of causing up to 90% of all colics – many of which are fatal. The most dangerous is Strongylus vulgaris, a pink-grey worm growing to 2cm long.

After worm larvae are picked up off pastures and swallowed by the horse they burrow through the large intestinal wall into arteries (blood vessels). Here they develop into adult worms over the next four months. The young adult worms migrate back to the large intestine where they attach to the walls, causing ulceration, bleeding and bouts of colic. The female worms lay eggs – up to 5,000 each day – and these pass out in the horse’s droppings onto pasture. In humid weather, eggs can become infective larvae in just 1 week and the cycle starts again. Refer to Internal parasite control in horses for more information.

The larvae of bloodworms are the real killers. During their time in the blood vessels, they inflame, weaken and injure the vessel lining, causing blood clots and clusters of larvae to form. The resulting pain causes intermittent bouts of colic.

In the most severe cases, the larvae can totally block the blood vessels, cutting off blood supply to the intestine, and causing the death of that part of the gut. Major surgery to remove the inflamed and dying intestine is the only treatment option.

4. Infections

Infections in organs such as the liver, uterus and spleen can cause symptoms of colic. In these cases, the horse will often have a raised temperature, lack appetite and have a general demeanor of being unwell.

5. “Twisted bowel”

For reasons still not well understood, a horse’s intestine can twist around itself, completely blocking the passage of intestinal contents. Food and fluid builds up in the gastrointestinal tract forward of the “twist”, causing pain and signs of colic.

6. Tumours

A not uncommon cause of colic is blockage of the bowel caused by fatty or other tumours. Often these tumours are quite small and benign, but they’re sometimes attached by a pedicle or “stalk” of tissue. This can twist around a piece of bowel, strangulating the intestine, blocking the passage of food and ultimately causing death of this section of the gastrointestinal tract.


Fortunately, most colics respond to veterinary intervention including pain relief and other relevant medications (paraffin oil, antibiotics etc depending on the horse’s symptoms).

We will often take a blood sample to determine the level of dehydration (an important pointer to the severity of the colic and its underlying cause), and a faecal sample to check for worm eggs. An accurate history from the horse owner is essential. This helps to determine, for example, if a simple change in diet has initiated spasmodic colic.

Always ring us immediately if your horse is showing signs of colic. Because colic can be caused by a multitude of husbandry and disease conditions, prompt veterinary attention is essential – not only to provide fast pain relief, but to help diagnose the underlying cause and initiate correct treatment as soon as possible.