Don’t take your dog’s digestive system for granted, says animal scientist Dr Jacqueline Boyd as she highlights how important digestive health is for our dogs.
Next time you prepare a meal for your dog, take a moment to think about what happens to that food once he eats it. We often take our dog’s digestive system for granted. Everything happens out of sight and unless there is a problem, we only see what goes in one end, and what comes out the other! Dogs depend on their digestive systems to break down their food into smaller particles that can be efficiently absorbed. This is essential so that nutrients in the food can be used by the body to fuel activity, provide building blocks for growth, and support day-to-day life processes, and it highlights just how important your dog’s digestive health is.
A dog's digestive system
The digestive system (sometimes called the gastrointestinal tract or alimentary canal) is the ‘tube’ that runs from your dog’s mouth to his bottom. It is involved in digestion from the point of food consumption to the end products. Dogs are described as monogastric. This means ‘single stomached’ and indicates the fundamental digestive differences between dogs and other species with much more complex digestive systems, such as ruminants (cattle for example) and hind-gut fermenters, such as horses and rabbits. In addition to having a relatively simple digestive system, dogs also have a short digestive tract in comparison to many other species and a relatively rapid digestive process.
Stages of digestion
Digestion consists of four stages occurring along the length of the digestive system:
- Ingestion of food, which involves locating and eating foodstuff s; this starts in the mouth.
- Digestion where ingested material is processed to break it down into smaller particles by mechanical and chemical processes that begin in the mouth and continue into the stomach and small intestine.
- Absorption of nutrients (the end products of digestion) occurs in the small intestine.
- Elimination is the end point of digestion and is when waste material and anything not digested or absorbed is excreted from the body via the rectum.
The mouth and dentition
Dogs have specialised teeth to acquire and process food. Notably, dogs have a structure called the carnassial apparatus. This is characteristic of carnivores and consists of a pair of teeth — one in the upper jaw, one in the lower. The teeth overlap and work like a pair of scissors. Despite having a carnassial apparatus, dogs are more accurately classified as omnivores based on their dietary intake of plant and animal material, in addition to natural scavenger tendencies. Even giant pandas have carnassial teeth, despite the majority of their diet being plant based.
The mouth to stomach
The oesophagus is the tube running from the mouth to the stomach. Food is moved by peristalsis, a series of muscular contractions that move material from the mouth to the stomach. It also aids mechanical processing of food. The stomach is a site of food storage and can greatly expand in the dog as a scavenger and ‘gorge feeder’; they would have eaten large amounts of food quickly, based on availability.
The stomach is where chemical digestion starts. This is thanks to digestive enzymes, substances that break down specific food components; for example, lipases break down lipids. Hydrochloric acid is also found in the stomach and is essential to break down food components (including bone) and provides a protective function against potentially dangerous bacteria. This is why our dogs often appear able to eat things that would make us very ill.
Stomach to large intestine
The stomach leads to the small intestine which has three distinct areas — the duodenum, jejunum, and ileum. This is where digestion continues, especially protein breakdown. Nutrient absorption also occurs in the small intestine, which is aided by the presence of villi — finger-like projections that increase the surface area to support absorption. As well as villi, cells lining the small intestine have microvilli on their surfaces, further increasing the area available for nutrients to be absorbed. The small intestine leads to the large intestine, where water is resorbed, and anything not already digested or absorbed is processed into faecal matter. This is then excreted from the rectum for us to pick up and dispose of!
Digestive problems
Dogs tend to have pretty robust digestive systems by virtue of evolving as opportunistic scavengers — eating things because they are available. However, sometimes digestion falters. Certain diseases and conditions result in the digestive system becoming inflamed and not working as effectively as it should. Dogs might show signs of
digestive upset or distress including vomiting, diarrhoea, or pain — often seen as dogs stretching, groaning, or being unable to get comfortable.
Sensitive digestive systems
Sometimes our dogs can have sensitive digestive systems that react to certain food types, ingredients, or even stress and activity. If you notice your dog having loose poos, vomiting, showing discomfort, or signs of other digestive problems, it is a good idea to keep a food/activity diary. This can help to identify common factors in consultation with your vet and can also be useful if an elimination diet needs to be considered.
Parasites of the digestive system
Parasites such as roundworms and tapeworms can affect digestion and cause blockages in extreme cases. Other parasites such as Giardia and Cryptosporidium can be picked up from infected environments, including drinking water. These can all cause digestive problems and reduce how well a dog utilises his food. This means that good parasite control and management approaches are important for your dog’s digestive health.
Digestive infections
Occasionally, bacterial and viral infections can affect dogs causing digestive upset and other signs. In many cases these are transient and limited in severity. However, it is important never to become complacent about digestive upset in your dogs. They are often very good at hiding signs of pain and distress from us. Similarly, vomiting and diarrhoea can result in dehydration and other nutritional concerns very quickly, especially in puppies. For this reason, if you are at all concerned, always seek timely veterinary advice.
How to help your dog have a healthy digestive system
● While your vet should always be the first port of call in the case of digestive illness, you can help support your dog’s digestive health through good management and diet.
● Always ensure fresh, clean drinking water is freely available and discourage drinking from puddles or dirty water sources (if possible!). Wash food bowls and feeding utensils, including toys, regularly.
● Try to make any dietary changes gradually to allow the digestive microbiome (the population of microorganisms that live in the digestive system) to adapt. This can also avoid transient digestive upset. Interestingly, some evidence suggests that dogs exposed to a diet rich in different ingredients might have enhanced digestive health.
● The health of the whole digestive system is dependent on the health of the microbiome. Prebiotics are food ingredients (often fibre-based; MOS and FOS are common ones) that provide a source of food for the microbiome and thus support digestive health.
● Similarly, probiotics are living microorganisms that we can provide to replenish the microbiome population. Probiotics (and prebiotics) are sometimes used to maintain health generally or can be used in a targeted way after digestive illness to support recovery.