Updated November 29, 2020
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.
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.
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.
Giardia is an extremely common cause of diarrhoea in puppies, and will even persist into adulthood if not recognised.
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.
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.
Do Antibiotics Cause Diarrhoea?
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.
Does Changing The Food Cause Diarrhoea?
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 are usually trickier to find and 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.
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.
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
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
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.
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.
By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. These blogs are from a series regularly posted on email and Twitter. Subscribe via email here to never miss a story!
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