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What Causes Diarrhoea in Dogs?

What Causes Diarrhoea in Dogs?

Written by Dr. Nandita Mirajkar, BVSc & AH, PhD, Scientific Affairs Lead at ilume

We get it. Diarrhoea is a gross topic and isn’t something most people want to read about. But here’s why you should.

Diarrhoea is amongst the most common conditions veterinarians come across in clinics, and almost 29% of dogs have probably experienced it within the previous month.1, 2 If your pooch isn’t already amongst those unfortunate ones, there’s a high chance they will be in the future.

Diarrhoea is a change in your dog’s faeces or defecation patterns.

This means that the faeces may either be unformed or watery, or are passed in larger volumes or more frequently than usual.3

Diarrhoea occurs when something goes wrong with the normal process of forming faeces.

In a healthy dog, digested food material moves through the bowel as necessary nutrients, fluids, and electrolytes are absorbed, resulting in well-formed faeces that are comfortably voided. 3-5

When a dog has diarrhoea, the digested food moves quickly through the bowel with excessive secretion of or insufficient absorption of nutrients, fluids, or electrolytes, resulting in unformed or watery faeces, sometimes with blood or mucus, that may be voided frequently or after straining.3-5

Diarrhoea by itself is not a disease, rather, it is a sign of an underlying issue.

That’s why your veterinarian will ask you some questions to understand what’s causing the diarrhoea and what diagnostic tests and treatment are most appropriate. So, put on your detective hat, and join us in understanding what’s going on when your dog gets the runs. 

- How long has your dog had diarrhoea? This will tell you if the diarrhoea is acute or chronic, and accordingly what treatment is required.

‘Acute diarrhoea’, which makes up almost 90% of diarrhoea cases, is quite common in dogs, starts suddenly, lasts less than two weeks, and resolves by itself or with basic symptomatic treatment.5, 6

In contrast, ‘chronic diarrhoea’, which is far less common, lasts for more than two weeks or recurs often, and requires targeted treatment depending upon the cause and diagnosis.5 As chronic diarrhoea persists for longer, dogs may show other signs such as vomiting, abdominal pain, loss of appetite, weight loss or dry hair coat.5

- Is there a change in the way your dog defecates? This will tell you which region of the bowel is causing diarrhoea, and that’s important information that helps decide next steps.

If your dog is passing faeces more often and after much straining, but voiding small amounts of semi-formed faeces with blood or mucus in it, it likely is because of an issue in the colon (large intestine) and is called ‘large bowel diarrhoea.3, 5

If your dog doesn’t show much change in the frequency, isn’t straining to void, and passes watery, dark, and occasionally fatty or frothy looking faeces, it likely is because of an issue in the small intestine and is called ‘small bowel diarrhoea’. 3, 5

Sometimes, although you may see more symptoms of either one, the diarrhoea can be caused by issues in both, the large and the small intestine, and that’s known as ‘mixed bowel diarrhoea’. 3, 5

- What colour is the diarrhoea? A colour change is a reminder for you to have a closer look at the faeces and your dog’s diet to understand what may be causing it.

Your dog’s faeces can often change colour because of something they ate, including foods like carrots or beets, grass, food colour / dyes, supplements, dental chews, or medications. Usually, the faeces return to normal colour once it’s been voided from the body, and there’s no need to worry about these minor changes.7

Sometimes though, colour change, especially when accompanied by diarrhoea, may indicate an underlying issue, so it’s best to have a closer look.

For instance, white spots are usually worms, red or black faeces may suggest bleeding in the digestive tract, grey/white/yellow faeces may be a sign of issues in the gallbladder, liver, or pancreas, and green faeces could be caused by accidental consumption of rodenticide.7, 8 Pink-purple (‘raspberry jam’-like) diarrhoea may be seen in haemorrhagic gastroenteritis (HGE), a serious infection needing immediate veterinary attention.

So how should you as a dog owner know when the colour change is normal and when it’s a concern? Keep an eye out for other changes in faeces or defecation, other signs that indicate a change in health or behaviour, or if this colour change has lasted for two or more days. Always reach out to your veterinarian if something seems amiss.

- Have you noticed any other changes in your dog? You would expect to see other changes in health if there’s a more serious underlying cause of diarrhoea that needs attention.

If it is caused due to an issue in the gastrointestinal system, it is called ‘primary diarrhoea’.5

If it is a sign of a disease elsewhere in the body, such as diseases of the pancreas, liver, thyroid, or kidneys, it is called ‘secondary diarrhoea’.5

In both types, you’d expect to see other signs that the dog is unwell. This includes vomiting, showing signs of a tummy upset (passing wind, bloated belly, rumbling sounds), bad breath, signs of being in pain, a change in appetite, thirst, urination, or defecation, weight loss, lethargy, weakness, dehydration, or a poor hair coat.5

- Can you think of any recent events that may have caused the diarrhoea? Diet, stress, or your dog eating something they shouldn’t be, commonly cause diarrhoea.

Did your dog devour spoiled food off the road or step in another dog’s faeces at the park? Did they get into the garbage, break into their treat box, your kid’s toy box or worse, get into your pest control supplies?

Did you recently change their food, or maybe you shared your dinner with them?

Did they recently travel or stay in a kennel? Was there a major storm recently that bothered them?

Life is busy and it’s hard to always keep track of the smaller details. Yet, they may give clues as to why your dog has diarrhoea. Dietary indiscretion (dogs eating something they shouldn’t, or overeating something thats would have been okay in smaller portions), and stress are some of the most common causes of diarrhoea in dogs.3, 5, 6, 9, 10

Most episodes of diarrhoea in dogs are mild and related to something your dog ate.

In fact, up to 78% of cases may resolve within two days, and only 10% may require veterinary treatment.10

Dogs who scavenge, have recently changed diets, eat home-cooked food, stay in kennels, or don’t have up-to-date immunisations are at a much higher risk of experiencing diarrhoea. The risk of diarrhoea also increases for males, younger puppies, those living in populated urban areas and in the summer months.6, 11, 12 You may notice that most of these factors enable a dog picking up food poisoning, infections (bacteria, viruses, fungi or protozoa) or worms that can cause diarrhoea, and also reflects their gut becoming irritated or inflamed and having difficulty digesting or adapting to what they’ve eaten.

Since the gut is linked with every part of the body, varied factors, ranging from mild to serious, may cause diarrhoea.

These include 3, 5, 13:

  • dietary (e.g., eating something they shouldn’t, a sudden change in diet, overeating)
  • infectious (viral, bacterial, fungal, protozoal, parasitic)
  • stress (e.g., recent travel, boarding, severe weather, environmental changes)
  • intestinal conditions (e.g., food-responsive enteropathy due to food allergy or food intolerance)
  • inflammatory (e.g., IBD)
  • extra-intestinal disorders (e.g., diseases affecting the pancreas, liver, kidney, and thyroid)
  • metabolic (e.g., hypoadrenocorticism)
  • neoplasia (e.g., mast cell tumour)
  • medications (e.g., antibiotics, NSAIDs, chemotherapy)
  • toxins (e.g., heavy metals, insecticides)
  • anatomic (e.g., bowel obstruction)
  • trauma (e.g., intestinal penetration)
  • miscellaneous (e.g., toxaemia, septicaemia) 

If you’re reading this list and your dog has diarrhoea, don’t panic! While the above list includes potential causes of diarrhoea, the most common causes are related to a dog’s diet, and in particular, scavenging.9

Not every runny poo needs a vet visit, but it’s important to know when to consult your vet.

If your dog doesn’t have any underlying medical conditions, is appropriately vaccinated and dewormed, and although they have diarrhoea, if they continue to eat, play, and behave normally, wait, and observe their next bowel movement. Uncomplicated diarrhoea may resolve on its own, or may respond well to basic at-home care.4, 14

If you notice other signs of your usually healthy dog being unwell, it’s likely there’s an underlying issue causing the diarrhoea, and it’s time to contact your veterinarian. They’ll tell you if tests are needed, and what treatment option is best for your dog. Keep an eye out for odd changes in your dog’s faeces (e.g., blood, mucus, colour changes, worms, foreign objects), if the diarrhoea has lasted for two or more days, if your dog has vomited more than once or their vomit has blood in it, if your dog isn’t showing much interest in food or water, and if your dog seems to have abdominal pain, dehydration (dry nose, gums and sunken eyes), weakness, lethargy, or appears to be losing weight.14 Other than this, if you have a young puppy, a senior dog, a dog with incomplete vaccinations or a known medical condition, or if you know your dog ate something toxic or dangerous, it’s important that you visit your veterinarian.4, 14

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  • O'Neill DG, Church DB, McGreevy PD, Thomson PC, Brodbelt DC. Longevity and mortality of owned dogs in England. Vet J. Dec 2013;198(3):638-43. doi:10.1016/j.tvjl.2013.09.020
  • Stavisky J, Pinchbeck GL, German AJ, et al. Prevalence of canine enteric coronavirus in a cross-sectional survey of dogs presenting at veterinary practices. Vet Microbiol. Jan 6 2010;140(1-2):18-24. doi:10.1016/j.vetmic.2009.07.012
  • Battersby I, Harvey A. Differential diagnosis and treatment of acute diarrhoea in the dog and cat. In Practice. 2006;28(8):480-488. doi:
  • Newsletter CUCoVMsD. Diarrhea: Worry or wait? Cornell University College of Veterinary Medicine.
  • Marks SL. Diarrhea. Canine and feline gastroenterology. 2013:99.
  • Stavisky J, Radford AD, Gaskell R, et al. A case-control study of pathogen and lifestyle risk factors for diarrhoea in dogs. Prev Vet Med. May 1 2011;99(2-4):185-92. doi:10.1016/j.prevetmed.2011.02.009
  • Nicholas DJ. What Your Dog's Poo Can Tell You About Their Health. Preventive Vet.
  • Englar RE. Changes in fecal appearance. Common Clinical Presentations in Dogs and Cats. John Wiley & Sons, Inc; 2019:647-670:chap 51.
  • Hall E. Canine diarrhoea: a rational approach to diagnostic and therapeutic dilemmas. In Practice. 2009;31(1):8-16. doi:
  • Hubbard K, Skelly BJ, McKelvie J, Wood JL. Risk of vomiting and diarrhoea in dogs. Vet Rec. Dec 1 2007;161(22):755-7. doi:10.1136/vr.161.22.755
  • Sævik BK, Skancke EM, Trangerud C. A longitudinal study on diarrhoea and vomiting in young dogs of four large breeds. Acta Veterinaria Scandinavica. 2012;54(1):1-9. 
  • Pugh CA, Bronsvoort BMC, Handel IG, et al. Incidence rates and risk factor analyses for owner reported vomiting and diarrhoea in Labrador Retrievers - findings from the Dogslife Cohort. Prev Vet Med. May 1 2017;140:19-29. doi:10.1016/j.prevetmed.2017.02.014
  • Armstrong J, Intervention G. Approach to diagnosis and therapy of the patient with acute diarrhea. Todays Vet Prac. 2013:20-56. 
  • Turner DB. Your Dog Has Diarrhea: What to Do and NOT Do. Preventive Vet.