The term colic, literally translated refers to abdominal pain in the horse. Colic in horses is responsible for more deaths than any other disease process other than old age. It is estimated that 14.6% of all equine deaths per year are secondary to colic. The cost of colic to the Equine industry in the U.S. is estimated to be $144 million annually with approximately 12,000 to 24,000 colic surgeries being conducted in any given year.

The gastrointestinal tract of the horse is essentially a one way system. As a consequence, any condition that impedes the normal movement of gas, ingesta, and fluid through the digestive tract may result in severe dilation and strangulation of the organs or blood supply to the affected portions of the digestive tract. Horses can not vomit or regurgitate and when seen, is usually considered to be a terminal event.

The most common clinical signs associated with colic include pawing repeatedly with a front foot, looking back at the flank region, or raising a rear leg or kicking at the abdomen. Additional clinical signs include lying down and rolling from side to side. The horse may be sweaty and there may be visually apparent abdominal distension. There is usually a loss of appetite, depression, and a decrease in the number of bowl movements. A horse may curl the upper lip and arch the neck, stretch out as if to urinate, or strain to defecate. A fever may or may not be present. It is not common to see all of these clinical signs. The clinical signs that are exhibited are typical of abdominal discomfort and pain. Unfortunately, the clinical signs that are seen do not necessarily relate to what portion of the digestive tract is being affected or whether surgery will be indicated or not.

The general types of disease resulting in colic include:

Flatulent colic- conditions that cause excessive gas accumulation in the intestinal lumen.
Simple Obstruction – conditions resulting in obstruction of the intestinal lumen.
Strangulating obstruction – an obstruction of the intestinal lumen combined with interference of the blood supply to the intestines.
Nonstrangulating Infarction – an interruption of the blood supply to the intestines alone.
Inflammatory colic – caused by enteritis (inflammation of the intestines) or peritonitis (inflammation of the lining of the abdominal cavity).
Ulcers – deep ulcers in the stomach or bowel.
Unexplained colic.

Physical examination may help determine the severity of the colic as well as the area of the digestive tract that is affected. Animals in shock will have pale or cyanotic (blue) mucous membranes. Often a higher heart and respiratory rate will indicate a more severe intestinal problem. The passing of a nasogastric or stomach tube may assist in the release of pressure and gas from the stomach. Analysis of the volume and color of the stomach contents may assist in the diagnosis.

The abdomen as well as the chest should be auscultated (listening for heart, lung and sounds of ingesta moving through the intestinal tract). The presence or absence of intestinal sounds may help localize the problem area. A complete lack of intestinal sounds is typically associated with ileus (lack of intestinal movement) or ischemia (lack of blood supply). The most definitive test is rectal examination where many areas of the digestive tract and major vessels may be palpated and evaluated. Ultrasound evaluation may help differentiate medical versus surgical cases. In severe cases, evaluation of the peritoneal fluid (abdominal fluid) may prove helpful.

Horses with strangulating obstructions and complete obstructions require emergency abdominal surgery, while the other types of colic may usually be treated medically.

Most cases of colic are mild and analgesia is all that is required. Medications most commonly used are non-steroidal anti-inflammatory drugs (NSAIDs) of which the most frequently used is flunixin meglumine or Banamine®.

Many horses benefit from fluid therapy that will prevent dehydration and maintain the blood supply to vital organs. In cases of simple obstruction, mineral oil is the most commonly used medication for the treatment of these impactions. In the more severe impactions or when sand is responsible for the impactions, psyllium hydrophilic mucilloid (Metamucil®) is more effective in breaking up the obstruction and is given through a nasogastric tube as is the mineral oil.

Endotoxins are released from dying, typically gram-negative bacteria in devitalized tissue. Death in fatal cases of colic is usually related to the absorption of endotoxins from the gut lumen into the systemic circulation resulting in an endotoxemia. Typically death is a direct result of hypovolemia (low fluid or blood volume) and cardiovascular collapse secondary to the endotoxemia. In non-fatal cases, the endotoxemia may affect the circulation to other parts the body such as the hooves, resulting in laminitis as a direct sequela to the endotoxemia.

Antiserum is available against gram-negative endotoxins and may be administered intravenously diluted in a balanced electrolyte solution. Broad-spectrum antibiotics are also indicated when the patient is septic.

When ischemia (deficiency of the blood supply to a certain area) is suspected, dimethyl sulfoxide or DMSO has been administered intravenously diluted to a 10% solution in a balanced electrolyte solution. The efficacy of DMSO for ischemia has not been verified.

When horses exhibit severe abdominal distress that is non-responsive to medical therapy, surgery is indicated. Other indications for surgery include cardiovascular deterioration, changes in peritoneal fluid, or the demonstration of an obstruction on abdominal palpation or ultrasound. The earlier surgery is preformed, the better the prognosis.

The most common area involved in colic is the large colon, followed by the small intestine, cecum, and small colon respectively.

Diets that are lower in fiber (grain diets) have been shown to decrease the water content in the colon due to the decreased ability of grain to bind water. Grain is also believed to increase the production of gas in the gut which predisposes the horse to tympany (accumulation of gas), distention, and displacement of the organs in the digestive tract.

Changes in feeding practices, especially a sudden increase in the amount of grain, has been linked to an increased risk of colic. Studies have shown that feeding >2.7 Kg of oats daily will increase the incidence of colic. In fact, the feeding of pelleted feed and sweet feed, compared to no grain at all increases the horse’s risk of colic. Horses with no grain intake appeared to be protected from colic when compared to those animals being fed grain or concentrate on a daily basis.

Change in the amount of hay is also significant in the development of colic. The change of one type of hay to another did not appear to be as important as the quality of the hay. Poor quality roughage with low digestibility or particularly coarse fibers can cause impaction colic. Horses fed on Bermuda grass have an increased risk of ileal impaction.

Studies have also shown that horses having colic were significantly less likely to have been fed on pasture, however the overfeeding of a horse on lush grass, especially clover, may result in tympany. Having a horse spending 100% of time in a stall was also significantly associated with an increased risk of colic. In fact, the less access a horse has to pasture in general increases their risk of colic. One of the best ways to control the occurrence of colic is adequate parasite control and the assurance that there is adequate roughage in your horse’s diet.


References:

Kane, Ed. “Complexity of Colic Magnifies Challenge of Isolating its Cause”. DVM. April 2007 Pp. 6E-12E.

Smith, Bradford. Large Animal Internal Medicine. 2nd Edition. 1996. Mosby. St. Louis. Pp. 125-128.

Kahn, Cynthia. The Merck Veterinary Manual. 9th Edition. 2005. Merck and Co. Pp. 202-220.

Orsini, James and Thomas Divers. Equine Emergencies Treatment and Procedures. 3rd Edition. 2008. W.B. Saunders Pp. 107-113.

Radostits, Otto and Clive Gay, et all. Veterinary Medicine. 10th Edition. 2007. Pp. 215-228.

Brown, Christopher and Joseph Bertone. The 5-Minute Veterinary Consult Equine. Blackwell Publishing. 2005. Pp. 378-379.