Why Does My Dog Have Diarrhoea?

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.

This page covers diarrhoea in general. Please also visit our page on how we treat the most common type of diarrhoea in dogs.

What Does Colour, Mucus or Blood Mean?

  • 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.

Knowing which part of the intestine it comes from can help your vet decide on the right treatment. It’s always a good idea to get a dog checked by the vet. Some simple diarrhoea caused by eating something silly can go away by itself within 24 hours. However, if it hasn’t passed by then, or if your dog is unwell, please see your vet.

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

Causes of Diarrhoea in Dogs

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

Eating Something Rotten
dog eat vomit

Dogs are masters of the ‘eat it and see if it’s OK’ philosophy. Sometimes it’s not OK. We discuss diarrhoea caused by eating the wrong thing here.

Viral Infection

In Adelaide, almost any dog who goes out not protected against parvovirus is at high risk of serious diarrhoea and death. Distemper, though now rare in urban areas, also causes diarrhoea early in its course. Read more about parvo and distemper in dogs here.
Coronavirus 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.

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 3 or more weeks. Most of these dogs by now have extra symptoms including:

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

The causes of this are usually trickier and require extra tests for diagnosis and treatment.

Pancreatic Insufficiency

Cause: a lack of digestive enzymes
Test: Trypsin Like Immunoreactivity blood test
Treatment: replacement enzymes and supplements.

Addison’s disease

Cause: a lack of steroid hormones
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).
Test: ultrasound examination, X-rays and exploratory surgery
Treatment: surgery


Many serious toxins of dogs such as snail bait cause diarrhoea but usually that’s not the main problem. Sometimes heavy metals such as Zinc and Lead can cause diarrhoea without many other signs.

Food Intolerance

Cause: immune-mediated or allergic response to food allergens.
Test: cure by elimination of the offending food item and recurrence when challenged with the item confirms the suspicion
Treatment: restricted diets. Read all about testing and treatment of food allergy and intolerance here.

Inflammatory Bowel Disease

Cause: unknown but suspected to be immune-mediated and genetic in origin. More common in the Weimaraner, Rottweiler, German Shepherd Dog, Border Collie and Boxer.
Test: Only diagnosed by first ruling out all other causes of diarrhoea, possibly including intestinal biopsies
Treatment: may need immunosuppressive drugs if no response to dietary or antibiotic trials.

Liver & Kidney Disease

Cause: Organ failure
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.


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