The small intestine (or SI, for short) is the same in horses as it is in dogs, cats or humans. It's made up of 3 segments - the duodenum, the jejunum and the ileum. The duodenum is the first section, just after it leaves the stomach and for about the next 12-16 inches (that's it - so, not much goes wrong with the duodenum!) The jejunum makes up the bulk of the small intestine, and the ileum comprises the last foot or so before it enters the cecum. There are minor variations in these structures, but we don't have to worry about them here. All this SI is suspended within the abdomen by a sheet of connective tissue called "mesentery". (If you laid a garden hose straight across a towel, then picked the towel up at all 4 corners it would create the same effect.) The mesentery brings blood supply to the intestines.
Once the horse goes to surgery, some questions still remain. (You can answer some of those questions at this blog.) The tissue is not always dead, and simply removing the obstruction can allow blood to flow back into it. If this occurs, then the tissue will regain a more normal color. If not, then that section of bowel has to be removed, and the cut ends reattached. This is referred to as an resection-anastamosis. If a small section, of bowel is compromised (a few feet), then chances of survival increase. However, if large amounts are affected, prognosis will drop quickly. A horse can have up to 50% of its small intestine removed, but taking 30-40 feet of SI out is a risky endeavor. Many times, the decision needs to be made whether to finish the surgery, or to euthanize while under anesthesia.
Small intestinal strangulations are one of the more severe types of colic. Treatment must be fast and aggressive, and even then it's not always successful. Always have a trailer readily available in case you need to transfer to a surgical facility. Time can be critical in these situations, and an hour can make a huge difference.