Dietary therapy is an important aspect of the management of intestinal disease in dogs. Therapeutic recommendations have classically focused on dietary rest followed by implementation of a highly digestible or "bland" diet. However, as our understanding of the pathophysiology of intestinal disease unfolds, it is clear that that no single diet is likely to be effective for every patient. The overall objectives of dietary modification are to enhance digestion and absorption of nutrients, support the mucosal barrier function, promote normal intestinal motility and function, decrease inflammation, and incorporate nutrients that have a positive effect on the small intestine and intestinal flora. In addition to these key objectives, dietary therapy for intestinal disease can be divided into four key strategies:
Diseases that respond to novel or hydrolyzed protein diets
Diseases that respond to high energy, high dietary fat
Diseases that respond to low levels of dietary fat
Diseases that respond to high levels of dietary fiber
Novel or Hydrolyzed Protein
Novel or Hydrolyzed protein diets are indicated for dogs with a diagnosis of dietary sensitivity or inflammatory bowel disease. Dietary sensitivity, an adverse reaction to food, is a term used to describe a clinically abnormal response to the ingestion of a particular food. The reason an immunological response against a specific protein (or food allergen) is mounted in certain individuals is not fully understood. Genetics, age, poor digestibility of proteins, a defective mucosal barrier, defective oral tolerance, and increased mucosal permeability are all predisposing factors for food allergy.
Highly digestible diets typically have digestibility values that exceed 85%. A highly digestible diet requires less gastric, pancreatic, biliary and intestinal secretions for digestion. This results in almost complete digestion and absorption in the upper small intestine so that minimal residue is presented to the lower bowel. Proteins that are incompletely digested have more potential to incite an immune response to the residual antigenic proteins and large polypeptides. Conversely, highly digestible proteins are completely digested to free amino acids and small peptides, which have less potential to elicit an allergic response. Therefore highly digestible protein should be selected for patients with intestinal disease.
Elimination diets and subsequent re-challenge with the original diet are the only way to confirm a diagnosis of food allergy in pets. The aim is to feed a complete and balanced diet while strictly feeding a protein and carbohydrate source to which the pet has never been previously exposed. Gluten sensitivity is a specific example of food hypersensitivity which has been documented in Irish Setters.
The antigenicity of dietary proteins can be minimized by enzymatic hydrolysis to produce low molecular weight protein hydrolysates. Decreasing the size of the proteins that are ingested reduces the chances of immunoglobulin cross-linking and subsequent mast cell degranulation. Hypoallergenic diets have been recommended for both the diagnosis and management of food hypersensitivity and inflammatory bowel disease in dogs. Dossin et al fed a soy isolate hydrolysate diet to eight dogs with biopsy confirmed inflammatory bowel disease. Within 4 weeks of feeding the diet, fecal scores improved in all 8 dogs, intestinal movements normalized in 6 of the 8 dogs, and the infiltration of the intestinal mucosa reduced in 2 of the 8 dogs.
Nelson et al reported that clinical signs resolved in 13 dogs with lymphocytic, plasmocytic idiopathic chronic colitis when they were fed a cottage cheese and rice diet. In 11 dogs, two commercial diets not previously fed to these dogs were successfully substituted for the initial test diet, without causing recurrence of signs. Only two of these 11 dogs subsequently tolerated a switch to diets that had been fed at the time of onset of signs of colitis. Patterson et al reported that 20 dogs that exhibited both a non-seasonal pruritus and gastrointestinal signs had either improvement or complete resolution when fed either a homemade fish and potato or commercial fish and soy based diet. Nineteen of the dogs were subsequently maintained successfully on the commercial food. Simpson et al evaluated the effect of a selected protein chicken and rice diet for the management of idiopathic chronic colitis. Within one month, clinical signs of straining, fecal blood, fecal mucus and fecal consistency were significantly improved. Within two months of dietary therapy, 90% of 11 dogs were stabilized and did not require drug therapy to control clinical signs of disease.
Fat
The selection of a diet with a high or low fat concentration depends on the origin of the intestinal disorder and the patient's clinical status. Fat is the most highly digestible of all the nutrients, with digestibility values exceeding 90%. High fat diets are energy dense, reducing the volume of food consumed at each feeding. Fat will slow gastric emptying and prolong digestion, which can be beneficial for some forms of intestinal disease. Twelve dogs with a confirmed diagnosis of chronic intestinal disease (exocrine pancreatic insufficiency, inflammatory bowel disease, bacterial overgrowth, acute or chronic gastritis) were fed a diet containing a high concentration of fat. The benefits of the high fat diet were readily apparent with improvements in appetite, weight gain, and resolution of clinical signs of vomiting and diarrhea noted at 15 and 30 days following institution of dietary therapy.
Of the energy-providing nutrients, fat digestion requires the interplay between the intestine, liver and pancreas. A deficiency of pancreatic enzymes impairs digestion and results in malabsorption of dietary nutrients. Bacteria in the intestinal tract can metabolize undigested fat to hydroxy-fatty acids which leads to secretory diarrhea in the large intestine. Bacteria also deconjugate bile acids further impairing fat digestion and absorption. For this reason, fat restriction is beneficial for conditions where fat may become available for microbial metabolism, for example in malabsorption syndrome, small intestinal bacterial overgrowth, or bile acid deficiency.
Unlike amino acids and monosaccharides which are absorbed directly into the blood stream, fat is discharged from enterocytes into lacteals and is transported to the systemic circulation via mesenteric lymph vessels and the thoracic duct. Lymphangiectasia, a disorder characterized by congestion and/or dilatation of lymphatic vessels, will impair fat transport. Therefore, restriction of dietary fat is clearly indicated for the management of some intestinal disorders.
A clinical study with 48 dogs with chronic diarrhea (exocrine pancreatic insufficiency, small intestinal bacterial overgrowth, malabsorption syndrome, colitis and idiopathic diarrhea) was conducted at the University of Edinburgh. All dogs had chronic diarrhea despite aggressive drug and dietary management. All dogs were transitioned to a low fat diet and 14 parameters of GI function were measured monthly for 5 months. A significant improvement in body weight, appetite, drinking habits, demeanor, coat condition, skin condition, fecal appearance, consistency and frequency of defecation, and a reduction in vomiting and copraphagia were reported.
Polyunsaturated fatty acids are essential for the maintenance of membrane integrity as constituents of membrane phospholipids and the provision of substrates for eicosanoid synthesis (prostaglandins, thromboxanes, and leukotrienes). Long chain ω fatty acids such as eicosapentaenoic acid and docosahexaenoic acid, directly compete with arachidonic acid for the lipoxygenase and cycloxygenase enzymes. Subsequent metabolism of eicosapentaenoic acid generates less inflammatory mediators such as LTB5, and PGE3 compared to the metabolism of arachidonic acid. In addition, the metabolism of eicosapentaenoic acid produces hydroxy-fatty acids that block the production of LTB4, a potent chemotactic factor, from arachidonic acid. Therefore, in general, ω fatty acids are anti-inflammatory compared with the derivatives of ω fatty acids. Fish oils have been suggested to improve the clinical status of human patients with ulcerative colitis and Crohn's disease. Indeed, many diets formulated for the management of gastrointestinal disease in pets have been enhanced with ω fatty acids.
Dietary Fiber
Fiber, which is the non digestible carbohydrate of plants, can be classified according to solubility or fermentability. Soluble fibers form a gel in water which delays gastric emptying and inhibits absorption in the small intestine. Insoluble fibers such as cellulose and oat fiber increase fecal bulk, fecal water content, absorb toxins and normalize both segmental and propulsive motility. Both insoluble and soluble dietary fiber may be beneficial in the symptomatic treatment of certain large bowel diarrheas since fiber helps to normalize transit time and increase fecal water content. By normalizing intestinal transit time, insoluble fibers are often recommended for patients with constipation.
Fermentable fibers such as beet pulp, pectin, guar gum, gum arabic, and fructu-oligosaccharides may have a positive effective on the mucosal barrier by stimulating the growth of intestinal bacteria such as lactobacilli and bifidobacter. These bacterial species have been shown to be beneficial to intestinal health by decreasing the growth of pathogens such as Clostridia and E.coli. In addition, they produce the short chain fatty acids butyrate, acetate and propionate, which provide fuel for the colonocytes. Short chain fatty acids enhance sodium and water absorption, increase mucosal blood flow and increase gastrointestinal hormone release. These mechanisms contribute to the trophic role that short chain fatty acids have on the intestinal mucosa, stimulating enterocyte and colonocyte proliferation.
Leib et al reviewed the medical records of 37 dogs diagnosed with chronic idiopathic large-bowel diarrhea. Twenty three of 27 dogs were classified as having a very good to excellent response to a soluble fiber supplementation. Diarrhea returned in 6 of 11 dogs when fiber supplementation was withdrawn.
Additional Nutrients of Interest
Mucosal atrophy typically leads to a decreased availability of disaccharidases and carbohydrate malabsorption. Bacterial overgrowth and decreased transport of monosaccharides by malfunctioning enterocytes can also contribute to carbohydrate malabsorption. Regardless of the mechanism, malabsorption of carbohydrates contributes to osmotic diarrhea. Therefore, diets formulated for pets with intestinal disease should use reduced quantities of highly digestible carbohydrate. Rice has long been considered the ideal carbohydrate of intestinal disease. White rice is highly digestible, gluten free, and has rarely been implicated in food hypersensitivity.
Glutamine long considered a non-essential amino acid, has been suggested to be particularly beneficial for intestinal health. Glutamine preserves the intestinal barrier function, increases brush border enzyme activity, promotes protein synthesis and aids recovery from intestinal injury. Glutamine is the preferred fuel source for enterocytes. It is also used as a substrate for denovo synthesis of purine and pyrimidine nucleotides for DNA and RNA synthesis. GIT epithelial have very high turnover rate, therefore glutamine now appears to be conditionally essential nutrient for optimal GIT function in starvation and stress. Glutamine supplementation has been reported to improve nitrogen balance, decreased mucosal atrophy, decrease bacterial translocation, and stimulate the immune system in humans and laboratory species.
The gastrointestinal tract provides a home to a diverse population of bacterial. Recent research is focusing on methods to manipulate the gastrointestinal bacterial population to improve health. Prebiotics are dietary substances, such as fructooligosaccharides (FOS), mannanoligosaccharides (MOS), inulin, resistant starch, or arabinogalactans (AG) that promote the health of beneficial bacteria in the gut and deter the growth of pathogenic bacteria, such as E. coli, Salmonella and Campylobacter. Williard et al evaluated the effect of 1% fructooligosaccharides in 16 IgA-deficient German Shepherd Dogs with small intestinal bacterial overgrowth. FOS supplementation resulted in significantly lower aerobic/facultative anaerobic bacterial colony-forming unites in the small intestine. The results of this study indicated that FOS can affect the population of bacteria in the small intestine in dogs with small intestinal bacterial overgrowth. Swanson et al reported that supplemental fructooligosaccharides (FOS) and (or) mannanoligosaccharides (MOS) have beneficial effects on colonic health and immune status of dogs.
Probiotics are live microbial feed supplements that are administered to improve the microbiological balance in the intestine. Baillon et al reported the ability of a probiotic strain to survive transit through the canine intestinal tract. Potential health promoting effects of the probiotic noted included increased phagocytic capability of neutrophils, a substantial reduction in serum endotoxin levels, and a lowering of erythrocyte fragility indices. Furthermore there was a significant decrease in the number of Clostridia reflecting a change in the colonic microflora towards a healthier balance. These changes are indicative of beneficial changes in immune function and intestinal barrier integrity, suggesting the possibility that probiotics could play an important role in protecting from disease.
Zeolite, or sodium silico-aluminate, a tetrahedral clay, is capable of absorbing bacterial toxins, bile acids, and gases. By forming a protective film on the intestinal mucosa, zeolite helps to enhance the intestinal mucosal barrier. Grandjean et al reported that the addition of clays to food decreased the duration and the severity of diarrhea in sled dogs. Clays have also been shown by Fioramonti et al to reduce diarrhea induced by experimental cholera toxin, in dogs.
References
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