Introduction

Nutrition is pivotal in the management of gastrointestinal (GI) disease, many cases being managed by dietary therapy alone. Diet has a direct effect on intestinal physiology, motility, cell renewal rate, microbiome, enzyme production, ammonia production, and volatile fatty acid content. Since most GI diseases are influenced by diet, it is vital to perform a good nutritional assessment. The World Small Animal Veterinary Association (WSAVA)'s Global Nutrition Committee (GNC) has developed guidelines for nutritional assessment.

Nutritional Assessment

Nutritional assessment has two parts: firstly a screening evaluation and an extended evaluation if areas of concern are found. The screening evaluation should be performed at every veterinary visit as part of routine history taking and physical examination. It includes a diet history, body weight, body condition score (BCS), muscle condition, and evaluation of the coat and teeth.

A good dietary history is crucial for patients with GI disease. Many diseases are caused by diet while others are benefited by a change in diet. You need to know everything the patient is fed. Often the pet has access to treats, foods provided to give medications, or outside food sources (e.g., scavenging or hunting) which the owner may not consider part of the "diet," so the questioning must be done carefully. The amount fed should be determined.

Other feeding factors include the frequency, timing, location, and method of feeding. Environmental factors include the pet's housing, presence of other animals, access to the outdoors, and environmental enrichment.

The 9-point body condition scale (BCS) is used by the WSAVA. Body condition is determined using a combination of the visual appearance and palpation of the pet. A video for determining canine BCS is available on the WSAVA website. A pet can be normal weight or overweight but still have muscle loss, especially ill pets and the elderly. Muscle mass scoring systems are based on palpation of skeletal muscle over the skull, scapulae, spine and pelvis. Acute and chronic disease may cause loss of muscle mass disproportionate to the loss of fat due to the cytokine and neurohormonal effects on metabolism. Muscle loss is often evident in pets with excess protein loss in their feces (protein-losing enteropathies). Muscle loss also occurs in many dogs when they are given corticosteroids.

Acute Vomiting and Diarrhoea

Previously, acute vomiting and diarrhoea was often managed by withholding food for 24 hours; however, when possible, it may be better to continue to feed small amounts of a highly digestible diet. Fasting affects the health of the intestinal villi and the microbiome and should be avoided if possible. The diet selection is ideally made with some knowledge of the ingredients in the previously fed diet and of any ingredients to which the pet may be sensitive. Highly digestible diets are easy for the stomach and intestines to process. Basically, they are primarily used for symptomatic therapy of acute gastroenteritis or as adjunctive therapy for symptomatic therapy of chronic gastric disease. They are not generally recommended for chronic diarrheas. They consist of diets that are low in fat (which is relatively difficult to digest for some patients with GI disease), low in fiber (which slows gastric emptying), and contain easily digested proteins and carbohydrates. Your grandmother gave you this type of diet when she fed you chicken noodle soup when you had the "flu."

Chronic Diarrhoea in Dogs and Cats

Chronic diarrhoea is diarrhoea which has lasted longer than 2 weeks and has many potential etiologies. Adverse reactions to food or food sensitivities are classified into two categories: food hypersensitivity which is synonymous with food allergy and is an immunologically mediated phenomenon; and food intolerance, which is an adverse reaction without an immunologically mediated basis. The signs are similar for both categories. Signs of adverse reactions to foods in cats and dogs usually affect the skin or gastrointestinal tract. Adverse reactions to food may occur when a food is first fed or after years of being fed the same food.

Adverse reactions to food are diagnosed using elimination-challenge trials. Dietary trials confirm or rule out adverse reactions to food but do not establish an immune-mediated basis for the reaction, although that does not affect the management of the case. Choosing a diet requires a very detailed history of what has been fed, as these ingredients should be avoided in the food chosen for an elimination trial. Alternatively, a hydrolyzed protein diet is often used as the hydrolysed proteins are usually less antigenic than whole proteins. The pet should be exposed to absolutely no other foods or ingredients during the diet trial as this would invalidate the trial making it impossible to confirm the diagnosis that diet is part of the problem. Counselling the owner on feeding management, including the feeding of treats or snacks, is key to the success of a dietary trial. Elimination diets can be used for patients with chronic small intestinal or chronic large intestinal diarrhea due to dietary allergy or intolerance. Dogs with antibiotic-responsive enteropathy often respond better if the antimicrobial therapy is combined with a high-quality elimination diet. Animals that respond to elimination diets usually do so within 3 weeks, although rare patients may require 4–6 weeks.

Therapy for protein-losing enteropathy due to intestinal lymphangiectasia is based upon feeding an ultra-low fat diet. Supplementation with medium-chain triglyceride oil (MCT) used to be recommended in these patients because MCT oil was supposed to bypass the intestinal lymphatics, thus preventing further rupturing of the lacteals and subsequent protein loss. Pancreatic enzymes were often added to the diet to ensure digestion of the medium-chain triglyceride oil. MCT oil is seldom used anymore because there are commercial ultra-low fat diets that have sufficient calories and are usually effective. A homemade ultra-low fat diet (e.g., white turkey meat plus potato or rice) can be used instead of a commercial diet, but it is almost never necessary. Such a diet can be so successful that it might occasionally be appropriate to use it as a therapeutic trial. Dogs with lymphangiectasia often show a marked increase in serum albumin concentration within 7–14 days of starting such a diet. If a homemade diet is used for more than a couple of weeks or used in a puppy or kitten, it should be balanced by a veterinary nutritionist, as many recipes on the web or online are not balanced.

Prebiotic and/or probiotic supplements are sometimes added to the diet. Prebiotics are complex carbohydrates which are fermentable, promote the growth of beneficial intestinal bacteria and decrease the growth of pathogenic bacteria (e.g., fructooligosaccharides and mannosoligosaccharides. Probiotics containing nonpathogenic bacteria, such as Bifidobacterium or Enterococcus faecium, are used to increase the ratio of normal to pathogenic GI microbes, which have a variety of effects on the intestine.

Some Specific Nutrients Used in Treatment of Gastrointestinal Diseases

Omega-3 fatty acids are helpful in many types of inflammation, although there are no good studies which examine their use in GI disease. When omega-3 fatty acids are fed, they replace some of the membrane omega-6 fatty acids and produce less inflammatory cytokines than those produced from omega-6 fatty acids. There are also some direct anti-inflammatory effects. Omega-3 fatty acids are found in oils from fish, such as menhaden, mackerel, herring, and sea salmon, which are rich in eicosapentaenoic acid and docosahexaenoic acid, and in plant oils such as flaxseed and canola oils which contain precursors for alpha-linolenic acid. The oils from fish should be used in dogs and cats as the plant sources aren't effective.

Dietary Fibre

Fibre is plant material resistant to digestion by the small intestine of dogs and cats. Dietary fibres include a wide variety of different materials, including cellulose, hemicellulose, pectins, gums, and lignins. Fibres have been divided into soluble and non-soluble types. Generally, soluble fibres attract water, form gels, delay gastric emptying, and are highly fermentable in the colon. Insoluble fibres may hasten gastric emptying, are not gel forming, are less fermentable, and provide bulk within the colon. Many fibre sources have properties of both classifications. The "crude fibre" reported on pet food labels is mostly insoluble fibre and does not include the amount of soluble, fermentable fibre.

Added dietary fibre is most often used for disorders of the large intestine such as colitis, and also for some types of constipation. Fermentation of fibre by intestinal bacteria produces short-chain fatty acids, which provide an energy source for the colonocytes, and lowers the pH of the colonic contents which helps impede the growth of pathogenic bacteria and decreases the absorption of ammonia. Insoluble fibres provide faecal bulk, aids in maintaining good faecal consistency and colonic motility. Many commercial pet food companies have developed diets with added fibre, and there are also fibre products which can be added to the food. Dogs and cats with chronic large-bowel diarrhea are often treated successfully with fiber-supplemented diets. In some cases, the high-fiber diet may be sufficient to resolve the clinical signs by itself. In other cases, initial treatment with tylosin or amoxicillin may be needed to make the patient respond, but the response is maintained by the diet. Animals that respond to high-fiber diets usually do so within 7–10 days.

Cobalamin

Cobalamin (vitamin B12) is deficient in many animals with severe or chronic GI disease. It is absorbed from the ileum and ileitis decreases absorption. Cobalamin is needed for GI epithelial cell turnover and repair, and in many cats with IBD, signs won't resolve until cobalamin deficiency is treated.