Penny is a 5-year-old spayed female mixed breed terrier who recently developed a problem with her bowel movements.

A few weeks ago, Penny began to have more frequent bowel movements.

The problem subsided, only to return with increased frequency and more volume.

Even more recently, Penny's stools have included a whitish gelatinous material and blood.

Dawn and Desmond, Penny's owners, are describing colitis. Penny has something wrong in her colon, which is the end of the line for the digestive tract.

The colon, or large intestine, is connected at one end to the small intestine and flows to the other end - the rectum.

The colon's main function is to absorb water from the stool. When the small intestine is done with the digestive process, the waste material enters the colon, along with a significant amount of water. The colon then reabsorbs much of the water, in essence conserving water while causing the stool to become more solid and formed. If the colon becomes irritated, this absorption process is disturbed and the stool is correspondingly less solid and more voluminous.

With more severe inflammation, the colon will produce a mucous secretion that appears as a gelatinous whitish material on and around the stool.

As the inflammatory process, colitis, continues, the colon wall can become irritated to the point of hemorrhage and, as a result, blood will be seen in the bowel movements.

Most cases of colitis are secondary, meaning there is a problem with digestion further up the digestive tract, usually the small intestine. There can be many causes, including parasites such as roundworms, whip worms, hookworms, protozoal parasites and so on.

There are too many possibilities that cause secondary colitis to list them all, but it is usually possible to distinguish primary colitis from secondary colitis by taking a radiograph of the abdomen to look at the bowel. If inflammatory changes are noted within the colon but not the small bowel, primary colitis is likely.

If changes are noted in the small bowel, then the noted colitis is probably secondary.

Penny needs to visit her veterinarian.

Most cases of primary or secondary colitis, once specifically diagnosed, are treatable and have a good prognosis. At this point, we do not definitively know the underlying cause of Penny's colitis. Once that determination is made, she can ride the road to recovery.

(Jeff Kahler is a veterinarian in Modesto, Calif. Questions can be submitted to Your Pet in care of LifeStyles, The Modesto Bee, P.O. Box 5256, Modesto CA 95352.)

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