The canine digestive system

Dogs require not only high-quality food, but – equally importantly – healthy digestion in order to absorb the maximum amount of goodness from their nutrition. Let’s take a closer look at your dog’s digestive system: the organs it’s made up of, how it works, how you can help your dog’s digestive system to remain healthy, the issues that could arise, and when to see the vet about your dog’s digestive system.

Organs of the canine digestive system

Your dog’s digestive system starts at his mouth and ends… under his tail. The components of a dog’s digestive system include:

  • mouth
  • oesophagus
  • stomach
  • liver (and gall bladder)
  • pancreas
  • small intestine
  • large intestine (colon)
  • rectum
  • anus

This shows just how many organs are involved in what we assume to be the simple process of eating and eliminating.

How does a dog’s digestive system work?

The aroma or anticipation of eating triggers the production of saliva in the dog’s mouth. Human saliva contains an enzyme (amylase) that starts the digestions process of starches, but dog saliva’s only function in the digestive process is to keep the mouth membranes moist and to lubricate the passage of food through the oesophagus and into the stomach.

When a dog has chewed up a mouthful of food, the contents he swallows are called a bolus. The bolus travels to the dog’s stomach along the oesophagus. The muscles of the oesophagus contract involuntarily in a one-directional wave – a process called peristalsis – that carries the bolus through the digestive system.

When the bolus reaches the stomach, the digestive process begins, thanks to the presence of highly acidic gastric juices and digestive enzymes. The stomach can hold a large amount of food, which is the evolutionary result of dogs not feeding regularly and the stomach being used to store food until they need to use the energy. Interestingly, swallowed food stays in the human stomach for far less time than in a dog’s stomach, but overall, our digestive process takes longer. Food passes through the human stomach in about 30 minutes; while it takes about six hours in a dog’s stomach (or less or more, depending on their size and digestive health). 

After the bolus has been subjected to processing in the stomach, it’s turned into a mushy substance called chyme, which enters the small intestine. Chyme is more liquid in consistency than the bolus, making it easier to break down and digest in the intestines.  

The small intestine is responsible for further breaking down and digesting food, but it’s also where nutrient absorption takes place. In order to help the process of fat absorption, the liver and gall bladder secrete bile into the first part of the small intestine (called the duodenum), which reduces the acidity of the chyme and aids the absorption of fat. What helps a dog digest food? The pancreas produces insulin to stabilise blood sugar and support the metabolism. It also secretes bicarbonate to alkalinise the digestible substances, and digestive enzymes to aid digestion.

In the next segment of the small intestine (the jejunum) the lining of this organ is covered in villi and microvilli – tiny ‘fingers’ that secrete digestive enzymes, absorb nutrients into the bloodstream, and prevent the absorption of waste materials. This is where amino acids (proteins) are absorbed into the bloodstream so they can be processed in the liver and used to support physical activity and maintain lean muscle in the dog’s body.

Peristalsis continues to push unabsorbed material through the last part of the small intestine – the ileum – that connects to the large intestine (colon). It is here that the last bit of moisture is extracted from the undigested material, which now accumulates and firms up as faecal matter. The colon moves this faecal matter into the rectum, out of the anus and onto your lawn. 

How long does it take for food to go through a dog's digestive tract?

Depending on the size and age of the dog, your dog’s food journey from mouth to rectum can take from eight hours (for small dogs) to 12 hours (for large dogs). This time directly correlates with the length of your dog’s digestive tract as well as their energy needs.

Puppies grow extremely fast, which requires a lot of energy. This fast absorption of nutrients means they need regular feeding to keep up with the energy demands of their rapid growth. Older dogs have a slower metabolism than younger dogs, which means their digestive process takes longer, especially since they don’t have as much of an energy need as younger or more active dogs.

How do you take care of your dog’s digestive system?

Feed your dog good food

All dogs’ digestive needs will be different, but the one rule of thumb for every dog is that they need high-quality food. In the early days of dog domestication, commercial dog foods didn’t exist, which meant that dogs were fed table scraps, waste foods, and sometimes – if they were lucky – the same foods that humans ate. Their digestive systems have adapted to ingest and digest whatever is available, but that doesn’t mean they automatically thrived from it. All dogs need the highest quality food you can afford, to meet their energy needs and to support a healthy digestive system.

Provide a probiotic

Many dogs also suffer from digestive upset and sensitive tummies, so their diets have to be adapted to ensure maximum nutrient absorption in spite of the problems. These dogs can benefit from a probiotic to help stabilise their gut bacteria. Similarly, some dogs will need digestive enzymes added to their food to help in the breakdown and absorption of nutrients, but these should not be over-used. Always confirm with the vet whether digestive enzymes could help or hurt your dog’s digestion. If necessary, the vet will recommend a prescription diet to help your dog with digestive issues.

Get daily exercise

As with humans, an integral part of good digestion is physical activity. This stimulates the digestive system to improve its motility (moving food along the small and large intestines) and to actively extract nutrients from food in order to use the caloric energy. A sluggish, sedentary lifestyle is not good for dogs’ digestive health at all – both humans and our canine friends can benefit from vigorous daily exercise and/or long walks!

What issues can arise with a dog’s digestive system?

Since digestion is such an integral part of a dog’s wellbeing, there are quite a number of problems that can occur in the digestive system, which are caused by genetics, allergies, poisons, stress, or simply bad food. Many of the symptoms of digestive upset are similar, since the body uses these processes to get rid of the toxin or allergen and to regain equilibrium, so it’s important to be aware of your dog’s habits, behaviours and what’s going on in their environment.

How do you know if your dog has a digestive problem?

There will always be some obvious telltale signs when your dog’s digestive system is being challenged – the two most obvious being vomiting and diarrhoea. A distended belly and/or abnormal noises in the gut (called borborygmi) can also indicate digestive distress. The less obvious signs include pain and inflammation, which may cause a lack of appetite or disinterest in food.

Common digestive issues in dogs

Since there are so many organs involved in a dog’s digestive system, there are many sites in the body in which issues can arise. Here, we look at a few of the more common digestive issues in dogs:

  • Obstruction – Dogs swallowing bones, a piece of food that is too large, or an inedible object can result in obstruction in the throat or oesophagus. They may retch or vomit to dislodge the obstruction. This is their body’s way of restoring equilibrium. Where an obstruction becomes stuck or embedded in the oesophagus or gut, surgery may be necessary for successful removal.
  • Mega-oesophagus – This is one of a number of structural issues that can occur with a dog’s oesophagus, making it difficult to eat and/or keep food down long enough for it to pass through the stomach.
  • Gastritis – Irritation or inflammation of the stomach can be caused by any number of things, but it disrupts the stomach’s ability to function normally. From bacteria and fungi, to toxins, viruses and even trauma, stomach inflammation can cause pain, vomiting, and changes in appetite.
  • Pancreatitis – While the underlying cause of pancreatitis can be many different things, an acute bout of it can be triggered by fatty food or some medications. Vomiting and diarrhoea are common symptoms of pancreatitis.  
  • Enteritis – Irritation or inflammation of the intestines caused by trauma, parasites, toxins or poor diet can cause vomiting and/or diarrhoea or other stool changes.
  • Constipation – Poor diet, not enough fibre, not enough water, or a problem with your dog’s motility could cause him to strain (painfully) and not produce any stool.
  • Diarrhoea – There are many, many causes of diarrhoea in dogs. See below about when to see the vet about your dog’s diarrhoea.

When should you see a vet about a dog’s digestive system?

A single bout of vomiting is relatively normal in most dogs, and is the primary way for a dog to get rid of a recently-ingested toxin. But if your dog vomits more than three times in a 24-hour period, or produces a yellow-greenish vomitus (which indicates the presence of bile), then it’s time to hurry to the vet, as this could be the symptom of a more serious problem.

Your dog may experience gastroenteritis at some point in their life, but gastro in puppies can quickly become dangerous to life-threatening. It’s best to treat digestive upset in puppies as a very good reason to visit the veterinarian.

Similarly, a bout or two of diarrhoea are nothing to worry about, but continuous episodes of watery stool can result in too much excreted water and the onset of dehydration, which is dangerous. If it doesn’t clear up after a day or two, take your dog to the vet. If you see blood in your dog’s stool, this indicates a more serious problem such as an ulcer, colitis, haemorrhagic gastroenteritis, pancreatitis or other intestinal damage or disorder. Never ignore excreted blood. Take your dog to the vet immediately!

Gastric dilatation-volvulus, bloat or torsion in dogs is a life-threatening medical emergency. It’s caused when the stomach (containing air) twists and blood supply to the surrounding organs is cut off. The dog can quickly go into shock and the condition may be fatal.

Chronic constipation can also have a number of simple or serious causes. If you see your dog struggling to pass his stool, it warrants a visit to the veterinarian to get him checked out.


This brief overview of the canine digestive system, its form and functioning, shows just how important it is to look after your dog’s eating and elimination habits. As part of a carefully calibrated collection of systems that make up Your Dog, the digestive system has a direct influence on the optimal functioning of those other systems too. We will cover those in future articles, so check back regularly to learn more about your dog’s body and how it works.

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