Ensuring the smooth passage of feed material around the horse’s lengthy colon is an important part of winter management. Rosie Naylor MRCVS discusses the causes and consequences of a pelvic flexure impaction


Horses are hindgut fermenters, having a large colon and a caecum within which hay is digested, and nutrients and water are absorbed.

The horse’s colon accounts for an incredible 13% of his bodyweight, compared to less than 0.5% in humans. One of the points where the large colon folds back on itself and narrows is called the pelvic flexure. This change in direction and sudden reduction in size predisposes development of a blockage at this location, a condition known as a pelvic flexure impaction.

When a pelvic flexure impaction occurs, feed material (ingesta) builds up in front of the blockage. This leads to stretching of the colon wall and intestinal spasm, causing signs of abdominal pain, commonly termed colic.

Pelvic flexure impactions are one of the most common causes of colic, accounting for between 12-40% of colic cases treated in the UK horse population. While these accumulations of dehydrated ingesta can occur anywhere along the intestinal tract, the pelvic flexure is the most common location.

Changes in a horse’s management, in particular a reduction in turn-out and exercise, are significant risk factors for developing an impaction — hence the increase in cases seen in winter months when horses tend to be stabled for longer. Horses on box rest are also at risk, for similar reasons, as are older horses and those with dental problems, who are unable to chew their hay or haylage as effectively.

Other triggers include abrupt changes in diet, the eating of bedding or feeding of poor-quality roughage. A reduced water intake, perhaps due to reduced availability when pipes are frozen, will rapidly lead to problems.

Occasionally, however, it is not possible to identify an underlying cause for an impaction. In the small number of cases where impactions recur, it has been suggested that an underlying disturbance in the motility of the intestines may play a role.

What are the signs?
Horses with a pelvic flexure impaction typically show mild to moderate signs of colic, such as pawing the ground, lying down or turning frequently to watch their flanks. Some roll or kick at their abdomen, while others may simply be quiet and off their feed.

There is often a reduction in the number of droppings passed. Any that do appear may be smaller, drier and firmer than normal.

These signs should prompt a veterinary examination, which often identifies a mildly increased heart rate and a reduction in gut sounds. The diagnosis is usually confirmed by examination via the rectum.

If discomfort is severe, further investigations such as an ultrasound examination of the abdomen may be performed to rule out another cause of abdominal pain.
Impactions can occasionally form as a result of dehydration secondary to a more serious cause of colic.

Managing with medication
Most pelvic flexure impactions can be resolved without the need for surgery, but it can take days.

Fluids administered via a stomach tube, in conjunction with intravenous fluids in severe cases, are the mainstay of treatment to rehydrate the impacted ingesta. Laxatives such as liquid paraffin or magnesium sulphate may also be added to the oral fluids.

Fluids are usually given along with pain relief as required, preferably at hospital where the horse can be monitored. Treatment is continued until the colic signs resolve, rectal examination confirms that the impaction has passed and droppings return to normal.

Feed may be withheld to prevent further enlargement of the impaction, but care must be taken to ensure that starved horses do not eat their bedding — especially straw. If there is any doubt, moving the horse to a stable with shavings or rubber matting is advisable. If this is not possible, or if the horse tries to eat the shavings, try using a muzzle.

Plenty of fresh water should be provided and gentle walking may be beneficial. When the impaction begins to pass, small amounts of grazing may be introduced to stimulate intestinal motility and to help clear the rest of the impaction.

The case for surgery
Once the impaction has resolved completely, feed can gradually be increased. Monitor the horse closely at this point for recurrence of colic signs and to make sure that he is passing droppings easily and frequently.

Most cases are managed successfully this way and the prognosis is usually very good.
Surgery is rarely necessary. It may be considered for cases that do not respond or for those showing unusually severe signs of pain, and may be unavoidable, if there is concern that the distended bowel has been damaged.

Simple management measures are usually sufficient to prevent the problem but some horses, such as those with dental problems, are prone to recurrent impactions. They may be best managed on a low-residue diet, where long-stem fibre such as hay is replaced by a complete pelleted high-fibre feed that is easier to digest.

This article was first published in Horse & Hound magazine (18 December 2014)