The Causes Of Diarrhoea In Dogs

Updated February 18, 2021

Diarrhoea is when dogs pass poo (faeces) that is softer than usual, more frequent or more is passed than normal. Vets call it diarrhoea any time faeces are less solid than usual, not just when they are watery.

Here I’m going to help you find the cause for your dog’s runny poop. First let’s look at what the mess itself can tell us.

Types of Dog Diarrhoea

Colour, mucus or blood can all tell you something about the origins of the problem.

• If diarrhoea has red blood or mucus, especially if a dog is also straining, it’s probably caused by a problem in the colon, or large intestine.
• If diarrhoea is yellow, brown or green, it probably has a small intestinal cause, especially if it’s quite runny.

Be careful: many causes of canine diarrhoea can also affect human health. Read about what you can catch from dogs here.

Causes of Acute Diarrhoea

Acute, or short-term causes of diarrhoea in dogs include:

Eating Something Rotten

Dogs are masters of the ‘eat it and see if it’s OK’ philosophy. Sometimes it’s not OK. We discuss the treatment of simple diarrhoea in healthy dogs here.

Viral Infection

In Adelaide, almost any dog who goes out not protected against parvovirus is at high risk of severe diarrhoea and death. Another serious viral disease, distemper, also causes diarrhoea but is now very rare. Read more about parvo and distemper in dogs here.
Canine coronavirus (not the human one) produces similar but milder diarrhoea and can be a problem in shelters and breeders.

Bacterial Infection

Salmonella and Campylobacter can cause diarrhoea in certain cases and are one of the reasons why we don’t recommend raw chicken be fed to dogs. Read more here on making safer raw diets for dogs.

Protozoal Infection

Giardia is an extremely common cause of diarrhoea in puppies, and will even persist into adulthood if not recognised.

Read here about the signs of Giardia infection in puppies.

Intestinal Worms

Yes, all worms regularly cause diarrhoea without regular use of dewormers, especially hookworms, roundworms and whipworms in dogs.

Haemorrhagic Gastroenteritis

HGE is a true emergency caused by a sudden onset of severe watery diarrhoea with fresh blood. Dogs are usually very lethargic, sick and vomiting. They rapidly go into shock from fluid and electrolyte loss and can die within hours if not treated.

The cause is unknown but recovery is usually rapid if fluid resuscitation can be given quickly enough.

Toxins

The most common ‘toxin’ to cause diarrhoea in dogs is medication from your vet! The best example is anti-inflammatories being used for arthritis treatment. If your dog is taking these and has diarrhoea, you need to stop at least until the diarrhoea goes away.

Sometimes heavy metals such as zinc and lead can cause diarrhoea, and many plants can cause diarrhoea if eaten. Signs and tests will depend on the toxin suspected.

Antibiotics

Yes, dogs can get diarrhoea from almost any antibiotic. If your dog has developed diarrhoea after starting a course of antibiotics, please contact your vet straight away. If a vet is not available, it’s probably best to stop the antibiotics unless the infection itself is life-threatening.

Diet Change

It’s very rare to see diarrhoea caused simply by changing brands of dog food. Dogs who get diarrhoea with diet change usually have been been fed large amounts of an unusual food. Examples could be feeding leftovers, raiding the kitchen cupboards or after eating a fatty marrowbone.

Causes Of Chronic Diarrhoea

We call diarrhoea ‘chronic’ when it goes for 2 or more weeks. Most of these dogs by now have extra symptoms such as:

• Nausea & vomiting
• Abdominal pain
• Not eating or a picky appetite
• Weight loss
• Harsh dry coat

The causes of chronic diarrhoea usually require extra tests for diagnosis and treatment. These include:

• Routine blood tests
• Specific testing based on suspicions
• Faecal testing
• Ultrasound and X-rays

These tests are chosen based on the vet’s suspicions. Each disease is listed below.

Pancreatic Insufficiency

Cause: a lack of digestive enzymes
Signs: weight loss with an increased appetite and pale, bulky, smelly faeces
Test: Trypsin Like Immunoreactivity blood test
Treatment: replacement enzymes and supplements.

Addison’s disease

Cause: a lack of steroid hormones
Signs: can be from only diarrhoea and vomiting to severe illness and collapse
Test: routine blood testing and ACTH stimulation test
Treatment: replacement hormone treatment

Obstruction

Cause: anything causing a partial intestinal obstruction can cause chronic diarrhoea. These can be a foreign body, a tumour or an intussusception (telescoping of the bowel).
Signs: reduced appetite and weight loss
Test: ultrasound examination, X-rays and exploratory surgery
Treatment: surgery

Liver & Kidney Disease

Cause: Organ failure
Signs: reduced appetite and weight loss
Test: routine blood testing should be enough to find it
Treatment: ideally a liver biopsy is required to treat liver failure, although even liver failure diets alone can help. Read here about the treatment of kidney disease.

Chronic Enteropathy

The last diseases are grouped together as chronic enteropathy, because they cannot be detected on the tests mentioned earlier. They often go by the following names:

• Inflammatory Bowel Disease
• Food Intolerance
• Food Allergy
• Food Responsive Enteropathy
• Antibiotic Responsive Diarrhoea
• Steroid Responsive Disease

The diagnosis and treatment of these diseases is discussed in Part Two: Chronic Diarrhoea in Dogs. Please visit if you have reached this point without a diagnosis.

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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here.