The digestive tract is something we don’t often think about in detail with our pets unless we are seeing problems such as vomiting, diarrhea, or constipation. This article delves a bit deeper into our dog’s digestion and how his diet can impact that. 

How does a dog’s digestive system work?


The dog’s digestive system takes a similar road to ours but with a few differences which are natural adaptations inherited from their wild ancestors.


The first place food enters is the mouth and chewing is the start of the process of digestion. Dogs are unable to grind food or chew side to side. Instead, they have teeth that are designed for tearing, ripping and gnawing, due to their predominantly carnivorous diet. This doesn’t stop them from tackling other foods though like fruit and veg.


Food is swallowed and, lubricated with saliva from the mouth, it moves down the esophagus (food pipe) by waves of muscular movements propelling it into the stomach.


A dog’s stomach can expand greatly to accommodate large meals. This is because dogs in the wild used to eat large quantities of meat in one sitting when an opportunity arose. Food is stored and partially digested here with stomach acids and stomach movements start to break the food down.

Small intestine

Food passes from the stomach into the duodenum (small intestine). Enzymes are added from the pancreas which helps to break down fats, as well as bile acids from the liver. Absorption of nutrients occurs across the walls of the guts as the food moves through this long passageway, heading into the large intestine.

Large intestine

Water and electrolytes leave the large intestine being absorbed by the body over the gut lining, making the stools firmer.


The fully formed stool is stored temporarily in the rectum before being passed out. Stools are a mixture of the body’s waste products and indigestible food material and should be well-formed in dogs (watery stools are a sign of diarrhea). Click here for a fecal scoring chart for images of ideal stool consistency.

How long does it take a dog to digest food?

The time taken to digest a meal can depend on the food type consumed. Some foods are digested much quicker than others. Also, the breed, age, and size of the dog can all impact digestion time too.

On average it takes around 8-10 hours for a meal to be fully digested by an adult dog, but it could be a bit quicker or longer than this, depending on other factors.


What is digestibility and why is it important?

Digestibility describes the amount of nutrients that are available for your dog’s body to use after digestion of its food. This is often used as a measure of the quality of different diets.

The ingredients used in pet foods are usually what determines how digestible it is, with egg whites, meat, and offal being highly digestible and grains like wheat and oats being much less so. This is mainly due to fiber content, with ingredients higher in fiber being harder to digest.

Digestibility is important as it dictates the amount of nutrients a dog receives from its diet as well as impacting things like stool quality and frequency – which is usually what most owners notice!

The balance needs to be right. Whilst ‘highly digestible’ may seem like a good thing, feeding a dog a very highly digestible diet with little or no fiber will lead to a small stool size, reduced frequency of defecation, and constipation. On the other hand, feeding a very low digestibility diet will cause food to pass through the intestinal tract more quickly, with increased gas production and loose feces.

Many manufacturers of commercial dog food will look at digestibility as a factor when developing their products. 

How to help your dog’s digestion


1. Feed meals rather than free feed.

Most adult dogs do best being fed once or twice a day, replicating their wild past where they would have a large meal and then rest before the next hunt or scavenging event. They don’t tend to be able to graze all day or have lots of small meals like humans might.

2. Avoid too many treats

You should stick to your dog’s normal diet where possible to avoid digestive upsets. Some dogs cannot tolerate lactose in milk and dairy products, resulting in diarrhea. Some fatty or greasy foods could irritate too or even contribute towards pancreatitis – severe and painful inflammation of the pancreas (a small organ near the intestines).

3. Get them tested

Other things can also upset your dog’s digestion such as parasites, bacteria, or viral infections causing vomiting and diarrhea. In some cases, historical disease like parvovirus can cause severe gut damage that makes it harder for your pet to digest their food.

4. Consider supplements

Probiotics can be of benefit for some dogs in these situations, but the evidence is fairly limited for cases of chronic diarrhea and poor stools. Probiotic supplements for dogs are aimed at increasing the number of ‘good gut bacteria’ to help with digestion. Your vet will be able to advise.

5. Consider a special diet.

Dietary management tends to have better effects for dogs with tummy issues. Your veterinarian will be able to advise you better on the diets available and what might be most appropriate for your dog, as well as any other treatment options your dog might require.

If you are thinking of changing your dog’s usual diet you should do so gradually to allow your dog’s system to adjust to the new food.

What happens to dog food that can’t be digested?

Food that cannot be digested passes relatively unchanged through the digestive tract, which may be why you sometimes see small pieces of material in your dog’s stools like grass or sweetcorn.

When dog food can’t be digested properly it is likely to pass more quickly through the dog’s system leading to a high volume of loose stools, sometimes with associated gas. This could occur when the food has a low digestibility (i.e it is very high in indigestible fiber), or if your dog has health issues preventing proper digestion such as inflammatory bowel disease (IBD) or other stomach upsets.

The role of exercise in food digestion


Just as in people, exercise is important in keeping the digestive tract in good order. Exercise encourages bowel movements and can help avoid issues such as constipation. If a dog is busy burning off energy through exercise, his body will be trying to process his food quicker and more effectively to provide him with more fuel.

Make sure your dog is receiving an adequate amount of food to match his exercise levels, otherwise he will start to lose weight. Similarly, more sedate dogs will need fewer calories than energetic or working breeds.


Hopefully, this article has given you some more insight into your dog’s diet and digestion. If you are seeing issues with your dog’s stool quality, then you should seek veterinary advice to rule out underlying health complaints. They will also be able to advise you on suitable diets for your pet too, in case changing their food could be beneficial.