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.
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.
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.
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.
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.
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! Have something to add? Comments are welcome below and will appear within 24 hours.
