Dietary management of chronic diarrhoea in dogs

Chronic diarrhoea – defined as diarrhoea of over three weeks’ duration (Purina Scientific Review, 2012) – is a very common presentation in clinical practice and, in many cases, is one in which dietary management is central. It is important to highlight that diarrhoea is only a symptom, not a diagnosis.

Successful management of chronic diarrhoea relies on identifying whether the disease is small or large intestinal in origin and, as far as possible, reaching a definitive diagnosis, since this will significantly impact treatment strategies. The diarrhoea may be due to intestinal disease or may be the result of secondary or systemic conditions such as Addison’s disease or liver or renal disease. Whilst discussion of diagnosis is beyond the remit of this article, Table 1 highlights some of the differences in clinical presentation between small and large intestinal diarrhoea.

Small intestinal diarrhoea

An appropriate diet to help manage canine small intestinal chronic diarrhoea should incorporate most or all of the following components. Some of these may vary in their importance or appropriateness for a particular condition (for example, limited antigen diets are of particular importance in the case of adverse reactions to food or IBD).

High energy density food 4 to 4.5kcal/g

This is useful in many cases to help combat weight loss that could result from nutrient malassimilation (Hand et al., 2011).

High digestibility, low residue

This helps to maximise nutrient availability, reduce expo-sure to dietary antigens and minimise complications from the presence of undigested food (eg osmotic diarrhoea, altered microflora) (Hand et al., 2011).

Protein of a high biological value, coming from a limited number of protein sources

This reduces exposure to ingredients that could cause a dietary allergy (adverse immunological reaction) or intolerance (non-immunologically mediated) (Purina Scientific Review, 2012). A reduced antigen diet reduces the risk of acquiring allergies to dietary allergens when tight junctions are disrupted. Maldigestion of poorer quality proteins can result in undigested material reaching the colon where it is broken down by colonic flora, producing higher levels of faecal water, which can worsen diarrhoea. It can also serve as a substrate for the growth of potentially pathogenic bacteria, and produce ammonia and sulphur-containing compounds, which can increase faecal odour and negatively affect the colonic mucosa. All of these cause further compromise to the gastrointestinal tract.

An appropriate level of mixed fibres (soluble and insoluble)

This helps to normalise gastrointestinal motility and slow colonic transit time to promote maximal absorption of colonic contents. Soluble fibres including inulin and oligosac-charides can function as prebiotics to selectively promote the growth of beneficial bacteria (eg Bifidobacteria) and provide nutritional support to the gastrointestinal mucosa and enteric cells. Fibre reduces the digestibility of the diet, so care should be taken to ensure it is not excessive.

Prebiotics incorporated into some pet foods include fructooligosaccharides (FOS), mannanoligosaccharide (MOS) and inulin (Purina Scientific Review, 2012), and have a number of supporting studies demonstrating benefits on digestive health in dogs. Prebiotics may also play a direct role in host defences and immunomodulation. Prebiotics are selectively fermented in the colon by beneficial micro-organisms such as Bifidobacteria to produce short chain fatty acids (SCFAs) including acetic acid and lactic acid. These organic acids are an energy source for colonocytes and reduce growth of potentially pathogenic bacteria.

High carbohydrate digestibility of more than 90 percent

High carbohydrate digestibility is advised (Hand et al., 2011); carbohydrate malassimilation can result in osmotic diarrhoea or bacterial overgrowth (Purina Scientific Review, 2012).

Low in fat

Fat malabsorption is associated with IBD, EPI, lymphangectasia and a number of other causes of small intestinal diarrhoea (Lecoindre et al., 2010). Fat digestion involves eight steps including the requirement of bile acids and pancreatic lipase. Absorption occurs predominantly via the epithelial cells at the tip of the villi, which are the cells most susceptible to mucosal injury. Thus, mucosal damage or deficiencies in pancreatic lipase or bile acids can result in fat malassimilation (Lecoindre et al., 2010).

A low-fat diet limits the quantity of malabsorbed fats that are fermented to hydroxylated fatty acids, and which can exacerbate diarrhoea. It also helps minimise fat malassimilation, bile acid malabsorption and consequential deconjugation of unabsorbed bile acids, and minimises increased mucosal permeability. Since fat delays gastric emptying, a low-fat diet is useful for any patients suffering from concurrent nausea or vomiting. Ideally, fat should provide a maximum of 15 percent of the total diet’s calories (Hand et al., 2011), and lower than this in some disease states.

Increased omega-3 fatty acids from fish oils

EPA and DHA help to maximise natural anti-inflammatory processes by modulating the generation and biological activity of inflammatory mediators (Lecoindre et al., 2010).

High palatability

This is important since many patients with chronic diarrhoea may suffer from inappetance.

Appropriate electrolyte levels

Chronic diarrhoea can cause abnormalities in electrolytes, eg sodium, chloride and potassium (Hand et al., 2011).

Antioxidants

It remains to be determined whether there are long-term clinical benefits of antioxidant supplementation for patients with chronic diarrhoea, but oxidation by free radicals will exacerbate any tissue damage and chronic inflammation. Antioxidants tend to be incorporated into most diet plans to help protect cells (LaFlamme et al., 2007).

Large intestinal diarrhoea

Causes of colitis include inflammatory bowel disease (IBD), irritable bowel syndrome (IBS), histiocytic ulcerative colitis in Boxers and food sensitivities. The three main dietary options to consider in colitis cases are:

• High digestibility (fat and digestible carbohydrate greater than 90 percent digestibility, protein greater than 87 percent)
• Increased fibre (with a blend of soluble fibres (particularly prebiotics) and insoluble fibres)
• Hypoallergenic (Purina Scientific Review, 2012)

Other dietary factors that may be of benefit in colitis include a low-fat diet to reduce irritation to the colon from hydroxylfatty acids and bile salts as well as increased omega 3 fatty acids to help reduce inflammation (Hand et al., 2011). These are similar to management in small intestinal diarrhoea.

The choice of diet should be based primarily on the nature of the clinical disease present. For example, in IBD and food sensitivities, a hypoallergenic diet is likely to be most preferable, whereas in IBS, increased fibre may be the most effective (Hand et al., 2011). Other patient factors should also be considered; for example, if an animal has a low body condition score, a high-fibre diet may not be helpful. Optimal case management will often involve a multimodal approach with consideration of the diet, medications and environmental management. The rationale behind each is summarised in Table 2, along with potential disadvantages of the diet.

Additional considerations

In most cases of chronic diarrhoea, and particularly small intestinal diarrhoea, food should be given in small meals, little and often. Given that commercial complete diets are balanced, more convenient for owners and designed to meet the nutritional needs of animals with gastrointestinal disease discussed above, these are recommended over a home-cooked diet in most cases, and particularly given that these patients will require long-term dietary management. Ideally, any treats given should provide a maximum of 10 percent of the daily intake and consist of the main meal (for example, many wet commercial diets can be “shaped and baked” by owners to produce shaped treats).

Nutritional supplements

Probiotics are live microorganisms which, when administered in adequate amounts, confer a health benefit on the host (Lecoindre et al., 2010), and they can be an additional useful nutritional aid in many cases of small and large intestinal diarrhoea. Within the pet food industry, they tend to be given as a supplement rather than incorporated into the food. They may help via several different modes of action, eg direct competition between pathogenic bacteria in the gut, creation of a hostile luminal environment for pathogens to grow and immune modulation and enhancement.

Though now quite commonly incorporated into the management of diarrhoea, there is variable evidence for their use. They are usually used as part of a multimodal approach where it is difficult to determine their specific impact on any clinical improvement. There is little regulation regarding their use, resulting in marked variability in the quality, strains and doses incorporated into products.

Within veterinary medicine, most commercially available probiotics are strains of Enterococcus faecalis but even between these, the strain of bacteria used – and the strength of evidence for its use – can vary. The clinician should critically assess the evidence for the particular strain and preparation of the probiotic before use, and ideally select a veterinary probiotic showing success for the disorder and species the veterinarian intends to use it for. Each animal will have a differing gastrointestinal microbiome and this, alongside other aspects of management, may influence how well any given probiotic works in a particular individual.

Another key consideration in chronic enteropathies is the level of vitamin B12. Many patients suffer from cobalamin deficiency, particularly those with a compromised distal small intestine, gut dysbiosis or EPI, and supplementation may be required. Whilst commercially available diets may have vitamin B12 supplementation, additional supplementation is usually required. This may be in the form of weekly parenteral subcutaneous injections of vitamin B12 (Lecoindre et al., 2010), or a veterinary-approved oral formulation.

Conclusion

Canine chronic diarrhoea is a commonly encountered condition. Appropriate nutritional support, tailored to the individual case and underlying disease, has an important role in management. Some of these nutritional aspects are similar for small and large intestinal disease, including reduced dietary fat and prebiotics, whereas other aspects, such as increased insoluble fibre, may be very beneficial for some patients with large intestinal diarrhoea but contraindicated in many types of small intestinal diarrhoea. Alongside a suitable main meal diet, advice on meal size and frequency of feeding and use of a probiotic should be considered.