Stanley L. Marks, BVSc, PhD, DACVIM (Internal Medicine, Oncology), DACVN
Associate Professor, University of California, Davis, School of Veterinary Medicine
Davis, CA, USA
This presentation will highlight the dietary management of common intestinal maladies in the dog and cat, including acute gastroenteritis, chronic small-bowel diarrhea (including inflammatory bowel disease), and chronic large bowel diarrhea.
Standard dietary recommendations for dogs and cats with acute gastroenteritis have been to withhold food for 24-48 hours, followed by the introduction of small quantities of a "bland" diet fed 4-6 times per day for 3-7 days. These dietary recommendations have stood the test of time but are based more on common sense than any specific research. Fasting the animal for a short period provides bowel "rest". This is traditionally considered of prime importance in the treatment of most gastrointestinal problems although it has been recently challenged in the treatment of diarrhea (see below) and is probably reserved for acute intractable vomiting. Short-term bowel rest is accomplished by completely restricting the oral intake of food. The gastrointestinal tract can also be afforded rest by feeding highly digestible diets that are rapidly assimilated in the proximal small bowel.
One theoretical justification for not feeding a vomiting dog or cat its usual diet is the observation in humans that acquired food allergies to proteins eaten during acute gastroenteritis can delay recovery. There is clinical and gastroscopic food sensitivity test evidence to suggest that the same phenomenon can also occur in the cat and dog-albeit at a very low frequency. However, these events are probably limited to significant mucosal insults where there is marked inflammation and increased permeability. In these instances, introducing a highly digestible novel protein or hydrolyzed protein is recommended. Small frequent feedings have been recommended in order to limit the duration of acid secretion at each meal and to minimize gastric distension, which can provoke nausea when the stomach is inflamed.
Boiled hamburger (with the fat poured off) and rice, cottage cheese and rice, or chicken and rice in an approximately 1:4 ratio are commonly utilized for managing acute gastroenteritis in dogs. Cats do not need a source of carbohydrate and can be managed initially with boiled chicken or hamburger alone for up to 2-3 weeks before balancing the diet.
The long-held belief in the value of bowel rest for the treatment of diarrhea has been challenged by the concept of "feeding-through" diarrhea. Recent studies of humans with acute diarrhea have shown that feeding through diarrhea maintains greater mucosal barrier integrity. However, most of these studies have been performed in people with secretory diarrhea. It is unlikely that feeding-though diarrhea is a sensible approach in the short-term management of dogs and cats suffering from acute diarrhea. These conditions are usually osmotic diarrheas and are often accompanied by vomiting and feeding usually exacerbates the vomiting and diarrhea. Without doubt, however, feeding of patients with chronic diarrhea is required.
Chronic Small Bowel Disease
Dietary modification is essential for the management of most patients with chronic small-bowel disease. Dogs with diarrhea associated with small-bowel disease should be managed with a diet that is highly digestible, moderately fat-restricted, lactose-free, gluten-free, containing a novel or hydrolyzed protein. In contrast to dogs, cats with small-bowel disease seem to tolerate diets containing higher levels of fat, and high fat diets (79% fat calories) do not appear to delay gastric emptying in the cat.
A fat-restricted diet is important in the management of a variety of gastrointestinal diseases in dogs, even though fat is a valuable caloric source and enhances the palatability of the diet. Fat delays gastric emptying in dogs, and fat-restricted diets appear to be better tolerated in a variety of gastrointestinal diseases. Malabsorbed fatty acids can also exacerbate the diarrhea and stimulate fluid loss.
Dietary Lactose and Gluten
Intestinal disease frequently destroys or reduces mucosal brush border enzyme activity, particularly lactase. Milk or other lactose-containing substances should therefore be avoided in patients with enteric disease since failure to digest lactose results in bacterial degradation of the sugar to volatile fatty acids which can cause an osmotic diarrhea. The lactose content of yogurt varies and is generally not recommended in the management of diarrhea. In addition, the organisms in yogurt have not been shown to colonize the bowel and displace the "unfavorable" microorganisms in either normal or diseased intestines. Gluten is a protein component of wheat, oats, barley, and rye, all of which should be avoided in patients with inflammatory bowel disease (IBD) in the event that the diarrhea is due to a gluten enteropathy.
Adverse reactions to dietary staple proteins are common in cats and dogs with chronic gastrointestinal disease, and can often be successfully managed by feeding novel-protein diets that are highly digestible. Remember that "novelty' is defined by what that particular animal has been exposed to. There are no protein sources that are inherently "novel" or "hypoallergenic". The protein source should be highly digestible because intact proteins are far more antigenic than polypeptides and amino acids.
Inflammatory Bowel Disease (IBD)
The inflammatory bowel diseases (IBD) are the most common causes of chronic vomiting and diarrhea in dogs and cats. Failure to eliminate known causes of gastrointestinal inflammation which can mimic IBD can result in frustration for the owner and clinician due to poor responsiveness of the animal to dietary or pharmacologic therapy.
The cause(s) of IBD are poorly understood, and most of the evidence for proposed causes in dogs and cats have been extrapolated from humans with ulcerative colitis and Crohn's disease. Caution should be heeded in making extrapolations across species, because human and canine or feline IBD are not synonymous. There is provocative evidence from clinical observations and animal models to incriminate normal luminal bacteria or bacterial products in the initiation and perpetuation of canine IBD. The clinical response to novel or hydrolyzed proteins suggest that dietary antigens may influence the pathogenesis of IBD.
Because the presumed pathogenesis of canine IBD involves hypersensitivity to luminal dietary or microbial antigens, therapy is aimed at removing any antigenic source of inflammation, followed by suppression of the cell-mediated inflammatory response in the gastrointestinal tract. It is important that the ingredients list of a putatively "hypoallergenic" diet be thoroughly evaluated, because diets with several protein sources (lamb, beef, rice, and wheat) are commonly marketed with a claim to hypoallergenicity. All flavored vitamins and flavored heartworm preventatives, table scraps, and raw-hide chews should be avoided during the feeding of the controlled diet.
A small percentage of dogs with severe IBD will fail to respond to commercial "hypoallergenic" diets containing intact protein sources, despite aggressive pharmacologic therapy. These patients may benefit from diets containing extensively hydrolyzed protein sources (Purina HA Canine Formula or Hill's Prescription Diet Canine z/d ULTRA and Feline z/d) or from home-cooked diets containing single novel protein and carbohydrate sources. Generally speaking, home cooked diets will have a higher digestibility than commercial diets.
Chronic Large-Bowel Disease
Dietary recommendations for the management of diarrhea associated with large-bowel disease is controversial, because the veterinary information is often derived from few data-based refereed publications and many uncontrolled clinical observations. The response to dietary therapy can vary dramatically from one patient to another, with some animals showing improvement on low residue, "hypoallergenic" diets, and others improving on less digestible diets containing soluble or insoluble fiber sources.
There is evidence to suggest that some forms of colitis may be associated with a dietary sensitivity similar to that observed with small bowel disease. The theoretical benefit for utilizing highly digestible "hypoallergenic" diets for patients with colitis is analogous to patients with small intestinal disease. Highly digestible commercial diets, without novel protein sources, have also been shown to be effective in the management of patients with large-bowel diarrhea. In one prospective study, 11 dogs with idiopathic, chronic colitis were treated for 4 months with a commercial restricted antigen diet containing protein sources limited to chicken and rice. Within 1 month of consuming the limited antigen diet, 60% of the dogs required no sulfasalazine, or a reduced dosage than when originally presented. Within 2 months, 90% were stabilized with no drug therapy.
High fiber diets containing soluble, insoluble or mixed fiber are frequently recommended for the treatment of chronic colitis. The use of soluble (fermentable) fiber in preference to insoluble (non-fermentable) fiber is sometimes advocated because most soluble fibers generate butyrate, the principle source of energy for the colonocyte, and other short-chain fatty acids. Short-chain fatty acids may lower the colonic luminal pH, impeding the growth of pathogens. The use of dietary fiber can have deleterious consequences. As dietary fiber increases, digestibility of essential nutrients decreases, which may result in nutritional imbalances, particularly if a marginal quality diet is being fed.
Fructooligosaccharides (FOS) are carbohydrates that resist digestion by the enzymes in the gastrointestinal tract and can be metabolized by the microbial species that colonize the distal small intestine and colon. The addition of FOS to feline diets at 0.75% (DM) did not affect duodenal flora, but it did increase the numbers of lactobacilli and reduce the numbers of E. coli in the fecal flora of healthy cats. Healthy German shepherds believed to have bacterial overgrowth were supplemented with FOS at 1.0% (AF) of their diet. Changes were recognized in the duodenal bacterial flora but these changes were of less magnitude than seen in normal dogs for these parameters. The clinical significance of these studies in cats and dogs with colitis is unknown.
Recently, treatment of chronic idiopathic large bowel diarrhea with a highly digestible diet and soluble fiber was reviewed in a retrospective study of 37 dogs. Treatment with a soluble fiber source (Metamucil), added to a highly digestible diet, resulted in a very good to excellent response in 23 of the 27 dogs that received supplementation. Dogs classified as having a very good or excellent response to soluble fiber supplementation received no other additional therapy except for occasional loperamide or diphenoxylate. Fiber supplementation was later reduced or eliminated in 11 dogs; diarrhea returned in 6 of them.
Polyunsaturated Fatty Acids
Manipulation of the dietary ratio of omega-6 to omega-3 polyunsaturated fatty acids (PUFA's) has the potential to reduce the inflammatory response in human ulcerative colitis and Crohn's disease patients. Diets enriched in n-3 fatty acids can result in the incorporation of the m-3 fatty acids into biological membranes, with a corresponding decrease in concentrations of the proinflammatory n-6 fatty acids such as arachidonic acid (20:4,n-6). The therapeutic potential of dietary precursor modulation by a fish-oil-supplemented diet (n-3 fatty acids), such as eicosapentaenoic acid (C20:5,n-3) and docosahexaenoic acid (C22:6,n-3) in the therapy of ulcerative colitis has been shown to result in a 35% to 50% decrease in neutrophil production of LTB4. Significant improvement in symptoms and histologic appearance of the rectal mucosa has been observed in several small series of patients with Crohn's disease and ulcerative colitis given fish oil at 3 to 4 g daily for 2 to 6 months in uncontrolled studies. However, a larger, randomized, double-blind trial comprising 96 patients with ulcerative colitis failed to reveal any benefit in remission maintenance or treatment of relapse on 4.5 g of eicosapentaenoic acid daily, despite a significant reduction in LTB4 synthesis by blood peripheral polymorphonuclear cells. It should be emphasized, however, that the anti-inflammatory actions of the fish oils, in addition to inhibition of LTB4 , include suppression of IL-1 and platelet activating factor synthesis and scavenging of free oxygen radicals.
Polyunsaturated Fatty Acids
Manipulation of the dietary ratio of n-6 to n-3 polyunsaturated fatty acids (PUFA's) has the potential to reduce the inflammatory response in human ulcerative colitis and Crohn's disease patients. The theoretical basis is the same as that for small intestinal disease. There are no reports in the veterinary literature demonstrating the efficacy of n-3 fatty acid supplementation in managing canine or feline large intestinal disease. Further research is necessary to establish a dosage of PUFA's and to determine the clinical benefits in dogs and cats with large bowel diseases.
Diet Selection for Large-Bowel Disease
The optimal nutritional approach for the management of large-bowel disease remains to be determined and varies from animal to animal. Three types of foods are frequently used in the management of large-bowel diarrhea; 1) highly digestible, low-residue foods, 2) fermentable fiber-enhanced foods, and 3) elimination or novel foods. There are a number of commercial diets available that meet these specifications. The supplementation of fermentable fiber sources such as psyllium or oat bran may be necessary in animals showing partial resolution of their clinical signs. Failure to respond to these recommendations may necessitate selecting another novel protein source diet, adding insoluble fiber to the diet, or further dietary-fat restriction.
References are available upon request.