Stuart Fitzgerald
Dr Stuart Fitzgerald (MVB MANZCVS, University College Dublin)
Frenchie on toilet

Diarrhoea is an extremely common complaint in dogs, and is one of the most common reasons for owners to present their pets to veterinary clinics. As well as being a problem in its own right, diarrhoea is a non-specific sign of many possible underlying conditions, and may sometimes require a thorough diagnostic work-up.

However, most cases are self-limiting and can be managed at home with a little guidance and a modicum of common sense. In this article, I aim to provide some information on the most common causes of diarrhoea, a practical approach to identifying when and how to manage episodes of diarrhoea at home, and how to identify when your dog might need veterinary attention for this complaint.

Types of Diarrhoea

Digestive system of the dog

Digestive System of the Dog

While this may not be a topic for the faint-of-heart, distinguishing the different types of diarrhoea is a very useful first step in determining the approach to treatment. By definition, loose faeces indicate some disorder in your dog’s intestinal function.

The intestine is roughly divided into two major sections: the small intestine and large intestine (or small bowel and large bowel). These two sections perform quite different functions, and so disorders affecting either portion result in the production of quite different faeces.

The Small Intestine

The small intestine is responsible for the digestion and absorption of food. It accepts digestive enzymes, acids, and alkalis from the liver and pancreas, while also producing some of these substances itself. These help break food down into useful constituents, such as carbohydrates and amino acids, which are small enough to be absorbed into the bloodstream for further processing. This absorption is an active process, which depends on healthy cellular function within the small intestine. This healthy function depends, in turn, on normal blood supply, blood glucose concentrations, whole-body metabolic rate, and a host of other factors.

The Large Intestine

The large intestine, on the other hand, is mostly concerned with (a) the absorption of fluid and (b) the storage of faecal material. The intestinal contents arriving from the small intestine into the large intestine are very liquid, and this material needs to be dehydrated to some extent to form normal stool. The large intestine reabsorbs considerable volumes of this water daily. A demonstration of this fact is the very hard, dry stool seen to be produced by an animal with constipation; the increased time the faeces spend in the large intestine is the cause for this in most cases. In healthy dogs, the normal storage of faeces means that most only need to defecate once or twice daily, when mucous produced by the colonic cells allows the smooth passage of this waste.

Small Intestinal Diarrhoea

In animals with diarrhoea, dysfunction of the small intestine results in the production of a high volume of diarrhoea, which contains undigested or unabsorbed nutrients, and therefore may be particularly foul-smelling. Because of the loss of these nutrients, many animals with small intestinal diarrhoea will lose weight and/or have an increased appetite. If large amounts of acids, alkalis, or electrolytes are being lost, these dogs may be depressed and lethargic. If the small intestine is severely inflamed or damaged, blood loss may be reflected in very dark or black faeces, an indication of the presence of digested blood.

Large Intestinal Diarrhoea

With large intestinal diarrhoea, failure to absorb water is the cause of the loose stool, which may be accompanied by excess mucous production and the presence of fresh blood because of colonic irritation. Because the large intestine is irritated, storage of faeces is disrupted, and the dog will exhibit urgency and increased frequency of defecation. Dogs with large intestinal diarrhoea are more likely to soil in the home because they are simply unable to make it outside, and are “caught short”.

Signs of Small Bowel & Large Bowel Diarrhoea

Of course, some dogs with diarrhoea have both a small and large intestinal problem at the same time, and may show overlapping signs. Nonetheless, identifying the signs associated with either location can be very useful.

Symptom Small Bowl DiarrhoeaLarge Bowel Diarrhoea
Frequency of Defecation Normal to Slightly Increased Greatly Increased
Volume of Faeces Increased Unchanged/Decreased
Urgency - ++
Straining to Defecate - ++
Excessive Mucous in Faeces Not Usually Present
Blood in Faeces Black Faeces (Bleeding from Stomach or Small Intestine) Fresh Red Blood
Weight Loss or Other Systemic Signs Possible Not Usually

Dietary Indiscretion

Feral dog eating rubbish out of a bin

Feral Dog Eating Rubbish (Stolbovsky /

In the majority of dogs with acute, sudden-onset diarrhoea, the cause is likely to be dietary indiscretion, meaning the dog has eaten something he shouldn’t. Most dog owners are all-too familiar with the scenario of their pet sticking his nose into some hedgerow while out for a walk, only for him to emerge chewing on something foul-smelling.

For every occasion on which we see our dogs eat something like this, there are probably half a dozen episodes we don’t witness. Dogs have very resilient digestive tracts, and on most occasions, these ill-advised snacks don’t cause a problem, but inevitably something will eventually be rancid or rotten enough to upset the gut, resulting in diarrhoea.

In a typical dietary indiscretion case, the dog is bright, alert, and well, apart from perhaps ruining the owner’s new kitchen rug overnight. Either small or large bowel diarrhoea may occur, and the dog may be drinking more than usual to replace fluids lost in the faeces. In this scenario, at-home management of the problem is indicated, unless your dog has other significant health issues, such as diabetes or hypoadrenocorticism, which we will discuss later in this article.

Home Management of Diarrhoea

Assuming your dog is otherwise well, the sensible approach to diarrhoea is to allow the intestines to rest while maintaining the pet’s hydration and electrolyte levels. Food which enters into a disturbed intestine is likely to cause further disruption, by drawing more liquid and electrolytes from the bloodstream into the gut, and even a simple case of dietary indiscretion can become a protracted self-perpetuating problem. By withholding food for 24 hours, you can give the small and large intestine a chance to fully empty and to rest. While withholding food, it is vital to ensure your pet is drinking enough, as dehydration is a common complication of diarrhoea.

Rice Water

A useful way to increase fluid intake while providing simple carbohydrates and electrolytes is to offer rice water on several occasions throughout the day. This is prepared by boiling one part white rice to four parts water in a saucepan for 10 minutes, pouring off the water, and allowing it to cool. The starch in the water provides some flavour, and acts as a source of energy for the dog during this period of fasting.

Chicken and Rice

Assuming the diarrhoea has resolved, a small amount of highly-digestible food, such as chicken and boiled rice, or an equivalent commercial food, should be offered. Your dog should be hungry, willing to eat, and not suffer a stomach upset after this meal. If this initial feed doesn’t cause any problems, a second small meal can be given four hours later, and this plain diet should be fed, little and often, for around three days, before slowly reintroducing his normal food.

If your dog either is unwilling to eat after the 24-hours fast, or has a recurrence of the diarrhoea, veterinary attention must be sought for further treatment and investigation.

Other Causes of Acute Diarrhoea

The signs of dietary indiscretion can overlap with mild or early forms of other problems. Intestinal infections can occur, either arising from other ill dogs, or picked up from the aforementioned hedgerow goodies. Bacteria such as E. coli and Campylobacter can rapidly cause signs of severe diarrhoea, and although infected dogs may initially appear well, they will usually become depressed and inappetant within the first 24-hours. Antibiotics and intravenous fluid therapy are needed in most cases – treatments which are likely to require your pet to be hospitalised. Other types of micro-organisms, including protozoa and viruses, can also cause similar symptoms.

Canine Parvovirus

In particular, canine parvovirus, which all dogs be vaccinated against, can cause severe bloody diarrhoea and vomiting. Affected dogs are severely depressed, dehydrated, and inappetant, and will have a high fever. These dramatic symptoms should leave an owner in no doubt about the emergency nature of the problem, and urgent veterinary attention is required. While adult dogs may be infected by parvovirus, puppies are usually more severely affected, and mortality rates reach around 50%.

Chronic Diarrhoea

Vet examines dog with bad stomach

Dogs with chronic or recurring bouts of diarrhoea warrant a full veterinary examination and investigation. At a minimum, these pets should have blood and faecal samples sent for laboratory evaluation. If their condition appears unresponsive to treatment, further investigations, including abdominal ultrasound examinations, will need to be performed. As outlined above, normal digestion and intestinal function is a complex and multi-faceted process, and a large number of intestinal and systemic disorders can result in the non-specific sign of diarrhoea.

Systemic Disorders

For dogs with a waxing and waning history of bloody diarrhoea, vomiting, and depression, hypoadrenocorticism should be ruled out as early as possible. This condition is caused by reduced function of the adrenal glands, which normally produce steroid and other hormones to maintain normal function of the gastrointestinal, cardiovascular, and immune systems. Episodes of diarrhoea may be sparked in dogs with hypoadrenocorticism by stress, and so are often noticed after periods of being kennelled, or indeed after undergoing veterinary procedures (e.g. dental work). Subnormal blood cortisol levels confirm the condition, which may then be managed by supplementing steroids in tablet or injectable form.

Liver disease is another common cause of diarrhoea that requires a detailed investigation. Many breeds (e.g. Bedlington Terriers and Dobermans) are predisposed to a range of liver conditions, although any dog may develop either acute or chronic problems in this organ, as it is tasked with detoxifying the blood, and so is exposed to a constant stream of noxious stimuli.

Chronic Intestinal Disorders

The intestine, too, is constantly challenged and exposed to antigens that are capable of causing damage or inflammation to the gut wall. The immune system is extremely active in the walls of the intestine, and so it is unsurprising that this defence system can sometimes go awry. Chronic intestinal inflammation, often termed inflammatory bowel disease (IBD), results in thickening of the intestinal wall, fluid loss, and reduced absorption of nutrients.

This may be due to chronic infection, parasites, or food sensitivities (e.g. gluten intolerance). In many cases, no underlying cause can be identified; however, all dogs with suspected IBD need to be thoroughly investigated for some predisposing, potentially curable, factor. Those with true IBD are likely to need lifelong immunosuppressive and dietary therapy.

The disorders listed above are merely a sample of the many conditions your veterinarian may diagnose following investigation of diarrhoea. Some other common causes include

  • Intestinal foreign bodies (toys, string, fruit stones)
  • Kidney disease
  • Intestinal tumours
  • Pancreatic disorders
  • Drug treatments
  • Overheating
  • Change in diet

Longer Term Care for Dogs Prone to Diarrhoea


Lactobacillus, "good" bacteria (Riccardoariotti /

In some dogs, it can prove difficult to identify a definitive underlying disorder, and yet they may suffer repeated bouts of diarrhoea throughout their lives. As vets, we often find ourselves discussing “sensitive stomachs”, and are left to manage these patients as best we can, preferably without resorting to the use of long-term medication. If you have found yourself in this position with your dog, it is likely you have tried all manner of things to manage the problem.

There are a variety of commercially produced foods available for such dogs, which are easy to digest and produce less irritant substances within the bowel. In addition, they will normally include a combination of simple sugars designed to nourish both the cells lining the intestine and the beneficial bacteria found in the gut. These “good” bacteria include species, such as Lactobacillus and Acidophilus, and a growing body of evidence indicates that they are vital for intestinal health, reducing inflammation and promoting immunity.

Providing a supply of these bacteria to dogs prone to diarrhoea is sometimes helpful, and commercial probiotic preparations are often advised. Though this is an area of much debate and active research, it has been proven that animals with intestinal disorders have a greatly disturbed bacterial population, and it intuitively makes sense that combatting this imbalance is likely to be beneficial.


Although diarrhoea can be caused by a range of significant health problems, both within the gut and elsewhere, many acute cases can be managed at home. If your dog is otherwise well, alert and active, then conservative treatment at home may be all that is required to resolve the problem. However, if he seems depressed or is off his food, or if you are in any doubt, always contact your veterinary surgeon for advice.