Dr. David Williams,
College of Veterinary Medicine Texas A&M

Dietary recommendations, just like individual patient responses to specific diet types, for dogs with large bowel disorders vary. Some patients respond more favorably to low residue highly digestible, "hypoallergenic" diets, while others do better on fiber augmented diets.

Fiber effects vary depending on fiber type (soluble vs. insoluble). Alterations related to soluble fiber include delayed passage of ingesta, which allows for more water absorption, and increases in bacterial flora and their by- products which occur secondary to fermentation of soluble fiber by the microflora. The latter effect results in increased fecal bulk. Soluble fibers tend to have high fermentability (insoluble fibers tend to have low fermentability). Degradative products of soluble fiber include butyrate (the principle energy source for the colonocyte) and other short chain fatty acids. Short chain fatty acids help lower the colonic luminal pH, which helps impede the growth of pathogens. Examples of soluble fiber types are oat bran and psyllium-containing products (psyllium products are a mix of both soluble and insoluble fiber sources).

Insoluble fiber also increases fecal bulk because it is poorly digested. With increased bulk there is colonic distention, which may then help normalize colonic myoelectrical activity and segmentation. This results in slower transit of stool through the colon. Slower transit provides more time for water absorption in the colon, and less fecal water, which often results in passage of formed vs. non-formed stool. Both soluble and insoluble fibers bind bile acids and aid in preventing deconjugated bile acids from causing large bowel diarrhea. Sources of insoluble fiber include coarse bran, canned pumpkin, and bran cereals.

The choice of a diet for dogs with large intestinal diarrhea depends on the condition. Dogs with mild acute large bowel diarrhea often respond well to a short course of metronidazole and/or sulfasalazine therapy (5 to 14 days). If the patient is already eating a high quality diet, there may be no need whatsoever to change the diet. If there is concurrent small intestinal disease, especially a protein-losing enteropathy disorder (e.g., moderate to severe IBD, lymphangiectasia), a highly digestible diet rather than a fiber augmented one is recommended, since higher fiber content can have the deleterious effect of decreasing digestibility of essential nutrients. In my experience, dogs with histiocytic ulcerative colitis often respond best to a combination of pharmacotherapy (e.g., sulfasalazine plus metronidazole plus tylosin) and a highly digestible low residue diet, preferably one which includes a protein source novel to the patient.

Some dogs with large intestinal disorders respond quite well to dietary management alone (either fiber augmented or bland and highly digestible). Supplementation of fermentable fiber sources such as oat bran or psyllium may prove beneficial. Well-balanced commercial diets. Dogs with mild colitis frequently respond to dietary management, and pharmacotherapy may be limited to short periods designed to help control flare-ups of inflammation, with the dietary component serving as the enduring form of therapy. It is recommended that animals with Clostridium perfringens enterotoxicosis be fed a fiber supplemented diet, since alterations of the colonic pH may help decrease the growth of pathogens.