The gastrointestinal tract plays a crucial and central role in the health of our cats and dogs. As the organ that facilitates the uptake, digestion and absorption of water and feed, its physiological function is essential to provide our pets’ bodies with the nutrients they need to utilise their full potential. The food we offer our pets is, therefore, not only crucial for the benefits that are obvious to us, such as ensuring adequate growth, maintaining a specific body weight and having a shiny coat. It also supports organ function, allowing our pets to stay internally healthy, even aiding in the management of diseases and supporting healthy ageing.
Without gastrointestinal health, however, the nutrients we provide for our pets cannot be adequately absorbed and thus cannot be utilised, which can compromise all other bodily functions. The impact of gastrointestinal health is, therefore, essential to allow our pets to make the best use of the nutrients we provide them in their food. This article outlines how we can use the power of nutrition to allow the gastrointestinal tract to work at its full capacity, ensuring the health of our dogs and cats.
The direct impact of nutrition on gastrointestinal function
The functionality and integrity of the gastrointestinal tract is directly impacted by an animal’s diet, but diet also directly affects the intestinal mucosa as well as the microbiota. There are various factors that moderate gastrointestinal function, impacting how our pets’ diets directly and indirectly contribute to the functionality of their gastrointestinal tracts (Figure 1).
Nutrition comes in many shapes and forms. Both the specific nutrient levels required for the animal’s biological function and how these nutrients are delivered to the intestinal tract are relevant. The careful selection of ingredients needs to be considered in the diet formula as feed ingredients with proven functional benefits can help to address specific health issues. Diet processing ensures food safety and allows nutrients to be biologically more readily available. All these factors also impact the microbiota as well as the intestinal immune system.
Just as our pets have individual needs, the variety of available diets provides individual support for each pet. Figure 2 shows an overview of the dietetic tools that can be used to ensure our pet’s health, including their gastrointestinal health.
The direct impact of nutrients on gastrointestinal function
Nutritional interventions need to integrate husbandry and management to address our pets’ genetic requirements on top of their physiological, metabolic and immunological needs. However, without adequate nutrition, the best husbandry and management actions will not achieve their desired outcomes (Table 1).
Nutritional interventions need to integrate husbandry and management to address our pets’ genetic requirements on top of their physiological, metabolic and immunological needs
|Fat||Fibre||Protein and amino acids|
|1. Regulation of gastric emptying|
3. Intestinal resection
7. Protein-losing enteropathy
8. Short bowel syndrome
3. Bacterial dysbiosis/diversity
4. Chronic enteropathies
2. Portosystemic shunt
3. Hepatobiliary diseases
4. Protein-losing enteropathy
5. Chronic enteropathies
6. Gastritis/gastroduodenal ulcers
7. Bacterial dysbiosis
8. Hepatic lipidosis
Fat is a very efficient energy source which, due to its high energy density and high digestibility, allows us to feed smaller volumes to our dogs and cats. This can be especially helpful when animals are too sick to eat large quantities or have a limited intestinal surface area for nutrient absorption (for example, after surgical resection due to a foreign body, a tumour or gastric dilatation volvulus). In addition, fat is very palatable, so cats and dogs like to eat foods with a high fat content. As such, high-fat diets can encourage them to take in sufficient calories when they are not feeling their best or need to increase their body weight. This is especially relevant when the gastrointestinal tract is in a state of malabsorption.
Fat is a very efficient energy source which, due to its high energy density and high digestibility, allows us to feed smaller volumes to our dogs and cats
When is fat useful?
Malabsorption can be defined as a loss of integrity and function in the intestinal barrier. This can happen as a result of a viral or pathogenic bacterial infection, or inflammation caused by allergies and microbial dysbiosis, among other pathological reasons. As a consequence of malabsorption, the passage rate of the intestinal digesta increases, and fewer nutrients are absorbed. The increased luminal content of nutrients can lead to osmotic diarrhoea, which further increases the problem. Depending on the cause of malassimilation and its effect on the large or small intestine, increased or decreased fat in the diet will be helpful. An increased fat level allows for efficient energy uptake from smaller portions. In addition, fat slows down gastric emptying, which can help to regulate intestinal transit time. However, any undigested fat that reaches the distal ileum and colon can stimulate bacterial fermentation, leading to osmotic diarrhoea. Therefore, the presence of steatorrhea should be monitored and the fat intake adjusted accordingly.
Several commercial high- and low-fat gastrointestinal diets are on the market to tackle these issues. Low-fat diets are also important when facing gastrointestinal diseases such as pancreatitis, lymphangiectasia and hyperlipidaemia, wherein the body’s fat metabolism is impaired. Due to this, the provision of a low-fat diet is key to the animal’s ability to manage these conditions.
Undigested fat that reaches the distal ileum and colon can stimulate bacterial fermentation, leading to osmotic diarrhoea. Therefore, the presence of steatorrhea should be monitored and the fat intake adjusted accordingly
Many types of fibres are known and used for their beneficial impact on gastrointestinal health in the veterinary profession. The functional characteristics of these fibres are mostly determined by their chemical composition and a range of feed ingredients that combine different fibre qualities exist. For example, you can determine the function of a fibre by presence and number of fermentable or non-fermentable, soluble or non-soluble and digestible and non-digestible fractions. Furthermore, different feed ingredients, such as barley, corn, psyllium, cellulose powder and beet pulp, can have different levels and combinations of these individual chemical fibre fractions. It is, therefore, crucial to understand that no two “high-fibre” diets are alike, and the list of ingredients and their inclusion levels are of great importance when deciding a patient’s diet.
No two “high-fibre” diets are alike, and the list of ingredients and their inclusion levels are of great importance when deciding a patient’s diet
When is fibre useful?
In general, fibre provides bulk, and this regulates intestinal transit time. As the fibrous bulk travels along the intestinal tract at its own pace, it can be very helpful for animals with diarrhoea or constipation. The volume of digesta cannot be transported as fast as “runny diarrhoea”, and the bulk provides a physical stimulus to the gastrointestinal wall to maintain rhythmic slow wave motility, which can help in dogs and cats suffering from constipation. The soluble fibres that bind water in the intestinal tract are especially beneficial for this physical stimulation; however, high levels of soluble fibres can hinder digestive enzymes from efficiently breaking down proteins and fats. Unfavourably high levels of soluble fibre thus reduce the overall nutrient digestibility.
Fibre provides bulk, and this regulates intestinal transit time [therefore] it can be very helpful for animals with diarrhoea or constipation
Fibres, especially fermentable fibres, can be broken down and utilised by the intestinal microbiota, thus serving as a very important microbial food source. The provision of fibre-targeting microbiota has shown to be essential to maintain the protective mucus layer of the intestinal enterocytes. Fibres included in the pet’s diet specifically for the purpose of bacteria digestion are called prebiotics, and they have been used in many pet diets for decades. Some of the most common prebiotics include oligosaccharides and inulin, which can be found in beet pulp, chicory, Jerusalem artichoke and wheat bran.
The provision of fibre-targeting microbiota has shown to be essential to maintain the protective mucus layer of the intestinal enterocytes
Because of the individual variable response of faecal quality in cats and dogs when provided with different levels and different types of fibres, a systematic trial and error approach can be required to successfully manage diarrhoea and constipation. The results, however, can be very rewarding. It is now well known that the use of fibres can abolish the need for antibiotics and/or steroids, especially in dogs with severe and long-term chronic enteropathies.
Protein provides energy and delivers individual amino acids, some of which are essential and must be consumed in food for the pet to survive. A suitable amino acid composition is therefore important, and this determines the quality of the protein and the digestibility of the diet. The digestibility of proteins directly affects gastrointestinal health. If an animal absorbs too many unnecessary amino acids, their liver and kidneys need to work harder, which can impair their functionality. This is especially true in elderly pets and those that already have clinical or subclinical liver or kidney diseases.
Why are proteins important?
Any protein that is unabsorbed when overly high quantities are fed or because the protein’s quality is not adequate to be fully digested can cause two major threats. Firstly, it can be a source of antigens: when an inflammation of the gastrointestinal tract results in a barrier breakdown, the larger protein molecules that usually remain in the lumen of the gut can come into direct contact with immune cells and cause further inflammation or even an allergenic reaction. Secondly, malabsorbed protein in the hindgut serves as a microbial feed source. In contrast to the (mostly) beneficial action of fibrolytic bacteria on mucosal health and short-chain fatty acid production, proteolytic bacteria are mostly associated with bacterial dysbiosis and are responsible for bad odour and flatulence as well as poor faecal consistency.
Dietary proteins, including functional proteins and peptides (IgG, lactoferrin), seem to be especially important in the maintenance of immune homeostasis and immune competence of the gastrointestinal tract. In addition, by modifying intestinal microbiota composition, the bacterial production of antimicrobial peptides can interfere with bacterial pathogens and their adhesion to the intestinal mucosa. (Some of the key benefits of the intestinal microbiota are listed in Table 2.) How the health of our pets can be maintained or improved by targeting a certain microbiota composition is still subject to intensive research.
Dietary proteins […] seem to be especially important in the maintenance of immune homeostasis and immune competence of the gastrointestinal tract
Essential protein characteristics of gut-friendly diets are reduced levels of fermentable protein in the hindgut, the supply of beneficial compounds such as functional proteins and peptides and, under certain circumstances, the administration of hydrolysed protein.
|Beneficial gastrointestinal microbiota function|
|Defence/immune system||Barrier function/structural support||Metabolic/nutritive support||Neuronal signalling|
|1. Produce antimicrobial factors|
2. Compete with pathogens for space
3. Compete with pathogens for food
4. Compete with pathogens for GI receptors
5. Immune signalling via conjugated linoleic acids, NF-κβ aryl hydrocarbon receptors, interferons, short-chain fatty acids and others
|1. Stimulate immune system development|
2. Stimulate mucosal barrier function
3. Stimulate mucus production
4. Stimulate IgA production
5. Stimulate tight junction tightening
|1. Produce short-chain fatty acids for enterocyte nutrition|
2. Synthesise vitamins
3. Control enterocyte differentiation
4. Control enterocyte proliferation
5. Regulate ion absorption
6. Ferment residual fibres and proteins
7. Ferment epithelial-derived mucus
|1. Gut-brain axis communication via production of serotonin, tryptophan, GABA, neurotrophic factor (BDNF) and others|
2. Produce secondary bile acids