The word "colic" simply refers to abdominal pain. Therefore it can occur as a result of pain associated with any organ in the abdominal cavity. Such organs include the intestines, liver, kidneys, bladder, uterus, ovaries, etc. However, we typically associate colic with pain of the gastrointestinal system. The pain occurs as a result of stimulation of nerve endings within the intestinal walls. Consequently, distension and ischemia of the bowel or tension on the supporting mesentery can all be sources of pain and therefore causes of intestinal colic.
The gastrointestinal system consists of many sections which basically make up one long tube. Swallowed feed goes into the esophagus, which is approximately 3 feet in length. The esophagus empties into the stomach. Causes of stomach pain include severe distension, ulceration, and trauma. Feed then empties into the small intestine, which consists of the duodenum, jejunum, and ileum. The small intestine is approximately 72 feet long. It is not a very forgiving organ, and tends to become easily inflamed if distended or twisted for any length of time. Small intestinal problems appear to be more common in the southeast than in other parts of the country. Impactions of the ileum occur frequently in the southeast and is often a consequence of feeding coastal Bermuda grass hay. Inflammatory disease, impaction, volvulus (twisting), and strangulation due to a lipoma are all causes of small intestinal colic.
The small intestine empties into the cecum, which is analogous to the human appendix. Its form is that of a large comma-shaped blind sac. Unlike our appendix, the equine cecum performs an important function in the bacterial fermentation and breakdown of feed. The cecum is more forgiving than the small intestine and abdominal pain is usually milder with cecal problems. However, problems such as cecal impactions or excessive cecal gas (gas colic) can last for days and sometimes weeks. Therefore, problems in the cecum can certainly be life-threatening. The cecum empties into the large colon, a very large organ shaped like a horseshoe. It can be as long as 20 ft. The large colon consists of a) the right and left ventral colon, which rests on the floor of the abdominal cavity just behind the stomach and liver, and b) the right and left dorsal large colon which sits atop its ventral counterpart. One end of the horseshoe is called the pelvic flexure and is not attached to the body wall. If given the opportunity, the large colon can become displaced. Colon torsion, nephrosplenic entrapment, and right dorsal displacement are all forms of large colon displacement.
The large colon empties into the transverse colon, which connects the large colon to the small colon. The transverse colon is shaped like a funnel. This is the area where intestinal stones or "enteroliths" tend to become lodged. The small colon is about 32 feet long. This is where the fecal balls ("road apples") are formed. The small colon is not able to tolerate much distention and therefore can be a significant source of pain. Ponies and Minis have an increased tendency to develop small colon impactions which can be life-threatening. The small colon is attached to the body wall throughout its entirety, and is therefore difficult to exteriorize from the abdomen. This makes small colon problems difficult to manage surgically. The small colon moves fecal balls into the rectum, which is the last stop before the stall floor.
Most rectal problems occur as a result of trauma during breeding (in mares), neurologic disease, or excessive manipulation during rectal evaluation. Most horses with colic can be treated successfully with conservative therapy. Others require surgical intervention to overcome the problem. It is important to recognize what separates surgical and non-surgical colics. Simply, surgical colics will usually not resolve without the help of a surgeons hands to remove the cause of the obstruction. Examples of surgical colics include large colon displacement or torsions, and small intestinal incarcerations.
Indications for surgery are:
- Severe abdominal pain,
- Abnormal rectal findings, and/or
- Excessive duration of pain, especially in the face of appropriate medical therapy
Colic surgery can be categorized as either complicated or uncomplicated, depending on the viability of the affected intestine. If the bowel has an adequate blood supply and is still alive, the problem can usually be corrected without removal of the affected segment(s). Prognosis for uncomplicated surgery is typically good. If blood supply to a portion of the bowel is compromised (as a result of distension, twisting, strangulation, etc.) it will not receive the oxygen and nutrients it needs to function. It is also unable to remove toxins that accumulate in the tissues. One function of the intestinal lining is protection of the body from a substance called endotoxin produced by intestinal bacteria.
This important job may become altered with changes in blood flow. Consequently, the body absorbs these toxins into the blood stream, creating a situation called "endotoxemia". Endotoxemia is the primary killer of horses with colic. It causes shock, organ damage, laminitis, and vascular anomalies. Therefore, severely compromised or "dead" bowel should be removed to prevent further absorption of endotoxins into the body. Complicated surgery involves resection of damaged bowel. Prognosis is not as good due to the potentially lethal effects of endotoxemia in horses.