Small Intestine Impaction - Horse

Introduction

Bermuda grass (Cynodon dactylon) Sourced from Mike, Wikimedia Commons

Small Intestinal impaction causes total or partial obstruction of the intestinal lumen resulting in colic. The obstruction is most often associated with ascarid impaction due to ascarid infection in young horses, or ileal impaction due to ingestion of Bermuda grass in the USA or tapeworm infection in the UK. Ingesta and fluid builds up proximal to the impaction and does not reach the absorptive large intestine, this results in systemic volume depletion and reduced cardiac output.

Impaction may also result due to postoperative ileus; the risk can be minimised by good surgical technique, appropriate postoperative care and the administration of prokinectic drugs.

Signalment

Foals and yearlings are particularly susceptible to infection with ascarids, impaction usually occurs following the administration of an anthelmintic with a high efficacy.

Ileal impaction is more common in younger animals which are at greater risk of infection with tapeworms such as Anoplocephala perfoliata.

Clinical Signs

Clinical signs are of simple small intestine obstruction. Typically the condition starts with mild signs of colic which then progress as the condition becomes established. There will be additional signs of parasite infestation, weight loss, diarrhoea and ill thrift, in cases associated with ascarid and tapeworm infection.

The severity and speed of onset of clinical signs is determined by the level of the obstruction. Proximal obstructions will progress more rapidly than distal ones.

Passage of a stomach tube will produce nasogastric reflux depending on the site of obstruction and its duration; for a proximal obstruction fluid will build up in the stomach after approximately 3-6 hours, and for a distal obstruction, after 12 hours. Gut sounds will decrease as the small intestine becomes distended and atonic.

On rectal examination the small intestine is palpable as distended loops; in the early stages of ileal impaction a tubular structure may be felt in the mid abdomen.

Clinical signs and rectal examination will diagnose the problem to the small intestine but it may not be possible to make a definitive diagnosis until the horse is taken to surgery.

See Colic Diagnosis in Horses

Ultrasound

Abdominal ultrasound reveals distended loops of small intestine which are frequently immotile.

Treatment

In cases of partial impaction medical treatment with laxatives, IV fluids and analgesia may be successful but surgical management is usually recommended for small intestinal impaction. A ventral midline laparotomy is carried out to gain access to the small intestine, in severe cases the impacted portion of the intestine is removed and an anastamosis performed. In mild cases the impaction may be manually reduced but the intestine must be inspected closely for viability and sections removed if they are damaged. In the case of ascarid impaction several enterotomies are usually performed.

See Medical Treatment of Colic in Horses

Prognosis

If the impaction causes complete obstruction to the small intestine then the prognosis is poor, with mortality rates of up to 92%.

Literature Search

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Small Intestinal Obstruction in horses publications

Refernces

• Mair, T.S, Divers, T.J, Ducharme, N.G (2002) Manual of Equine Gastroenterology, WB Saunders.
• Merck & Co (2008) The Merck Veterinary Manual (Eighth Edition) Merial