Thursday, February 18, 2010

Thurs 2/18/2010 - Colic

Vet Tip of the Day: What is Colic?
Key Words: gastrointestinal, endotoxin

I had a special visitor today.  Dr. James Moore, from the University of Georgia, was in Reno speaking at the AERC National Convention.  Dr. Moore was my major professor when I completed my doctoral research back in the early 90's.   He is a brilliant surgeon and researcher, and has spent much of his career investigating the factors that make colic such a deadly disease in horses.  As we ate pizza and swapped old stories this evening, I thought I would use his visit as inspiration for today's Vet Tip of the Day.

Colic is a very general term that refers to pain originating from the abdominal region.  In horses, colic has been associated with any disease of the gastrointestinal (GI) system that causes clinical signs of  GI pain.  The most common mechanisms of GI pain are distension and loss of blood supply.  Both of these occur when a section of bowel shifts into an abnormal position, or rotates on its own access.  The equine gastrointestinal system is composed of the esophagus, stomach, small intestine, cecum, large colon, small colon and rectum. The large colon is divided into 4 sections, which lie folded on each other, running along either side of the abdominal cavity. The intestinal tract of an adult horse, from stomach to rectum, is over150' in length!  Here's the most amazing part: the vast majority of the intestinal tract is free to move all over the abdomen,  only the cecum is attached at its base to the body wall.  Therefore, whenever the horse's complex intestinal motility pattern is upset, loss of coordination in progressive motility can lead to displacement of portions of the small intestine, or any of the colons.  When this occurs food material cannot move in an organized manner through the GI system.  When food transit is slowed, the bowel wall becomes distended.  This distension causes pain and further disrupts motility.  If the bowel rotates on itself (torsion or volvulus), a complete obstruction occurs, with loss of blood supply and severe distension, which can rapidly lead to death.

What kills horses with severe colic?  When a piece of the intestinal tract loses motility, becomes distended, or has reduced blood supply, several things happen.  First, the contents of the intestine stop moving. Second, the wall of the intestine begins to lose integrity as its oxygen supply is cut off due to lack of blood supply.  The intestinal contents are normally rich in bacteria which aid digestion.  However, when gut contents stop moving, the chemical environment in the gut contents is altered, resulting in bacterial death.  The dead bacteria decompose, and are absorbed across the now unhealthy gut wall into the blood stream.  One of the components of the bacterial cell wall is called endotoxin or lipopolysaccharide.  Endotoxin is a very powerful toxin to which horses are exquisitely sensitive.  Very small amounts of endotoxin in the equine blood stream cause severe inflammation, which leads to shock, cardiovascular collapse, and ultimately death.  So horses which die due to colic are actually poisoned by the contents of their own gastrointestinal tract.

Less serious colics, caused by temporary delay of transit through parts of the gut, such as large colon impactions, often respond to conservative treatment including anti-inflammatory analgesic medication such as flunixin meglumine (Banamine) combined with administration of fluid, and mineral oil via a naso-gastric tube.  When a complete obstruction occurs, however, surgical intervention is necessary to empty the affected bowel and return it to a normal position.  In the most severe cases, where segments of bowel have had severe compromise to their blood supply, surgical resection (removal of the affected bowel) may be necessary.

Can you list 5 signs of colic (gastrointestinal pain) in order or increasing severity?
Do you know what the 2 most reliable indicators are to determine whether a horse with colic requires surgery?

Answers in tomorrow's Tip of the Day.


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