Causes of chronic diarrhoea in pets

Diarrhoea is defined as a change in the frequency, consistency or volume of faeces. It is a common sign of illness in both dogs and cats.

Acute versus chronic diarrhoea

Diarrhoea can be either acute or chronic. Diarrhoea that persists for more than two weeks, or that recurs frequently, is generally defined as being chronic. Dogs and cats with chronic diarrhoea generally require some diagnostic investigations and specific treatments to cure or control the cause of the disease.

Acute diarrhoea

In most instances, acute diarrhoea is self limiting and clears up on its own within 24 hours or so. Not all dogs and cats with acute diarrhoea will need to see a vet but you should always contact them for advice if you have any concerns at all about their health.

Things you can do to help your cat or dog if they have acute diarrhoea:

  • Withhold food for 12 hours
  • Gradually reintroduce bland foods in small amounts every few hours. Pasta and potato based meals with boiled white fish or chicken for protein are often good choices
  • Wean them back onto their original diet, if the diarrhoea has resolved within 24 hours
  • Make sure your pet has constant access to fresh water

However, there are instances when the above approach is unlikely to work and a vet’s help may be necessary. The list below describes some warning signs that should prompt you to take your pet to the vet.

  • Diarrhoea that persists for longer than 24 hours
  • Diarrhoea that contains blood. If the blood originates from the stomach or small intestine it will make their stool black and often it will also be tar-like in consistency (melena). Bleeding from the large intestine results in bright red blood in the stool
  • Diarrhoea accompanied by vomiting
  • A dramatic loss of appetite, particularly if your pet is not drinking
  • Dullness, depression and lethargy
  • Evidence of abdominal pain. This may manifest itself as a reluctance to be touched or stroked along the abdomen. Some dogs will adopt a prayer position where they crouch down with their forelegs extended

You should also contact your vet if your pet:

  • Has any previously diagnosed or ongoing illness and particularly if your pet is receiving any medication
  • Is very young (a puppy or kitten)

Chronic diarrhoea

As mentioned above, the term chronic is used to describe diarrhoea that persists or recurs despite treatment. In the majority of instances, this is a syndrome that needs further investigation before a diagnosis can be made.

Causes of chronic diarrhoea: intra- and extra-intestinal disease

Intuitively, you’d expect the cause of chronic diarrhoea to be in the gut. This is called primary gastrointestinal (gut) disease or intra-intestinal disease.

However, the gut is a huge organ and so diseases primarily affecting other organs in the body can secondarily affect the gut and result in diarrhoea. This is called extra-intestinal disease. In this case, the gut can be seen as an innocent bystander that has been caught up in the action. This distinction is important because it affects the diagnostic tests that are considered in order to arrive at a diagnosis.

Examples of diseases that result in chronic diarrhoea

Important note: the lists below are not comprehensive, and the likelihood of any individual being affected with a particular disease depends on numerous factors, such as their species (cat/dog), age and breed.

  • Intra-intestinal disease
    • Infectious diseases: e.g. parasites, viral, bacterial and fungal diseases○ Partial obstructions: e.g. foreign objects and tumours (cancer)
    • Inflammation: e.g. inflammatory bowel disease, breed-associated disorders (e.g. Besanji enteropathy), dietary intolerances and allergies
    • Other disorders: e.g. antibiotic responsive diarrhoea, lymphangectasia, irritable bowel syndrome and cobalamin (Vitamin B12) depletion
  • Extraintestinal disease
    • Pancreatic disease: e.g. pancreatitis and exocrine pancreatic insufficiency
    • Liver disease: e.g. portosystemic shunts and hepatitis
    • Hormonal disease: e.g. hyperthyroidism (cats) and Addison’s disease (dogs)
    • Cardiovascular disease: e.g. heart failure and vascular occlusions

Diagnostic investigation of chronic diarrhoea

The type of tests and the order in which they are selected differs from patient to patient but investigations always start by collecting a thorough history and carrying out a careful clinical examination. Very often these will provide information that dictates what the next steps should be. The following tests are therefore not listed in any particular order.

Blood tests: These are useful for assessing the overall health of a patient and also for detecting or excluding extra-intestinal diseases, such as those listed above. Cobalamin deficiency can also be detected via a blood test.

Faecal analysis: This is particularly useful for detecting infectious disease in young animals, as they are generally more prone to picking up infections. Many infectious agents are only shed intermittently in the faeces and therefore to improve accuracy, faecal samples are sometimes collected on three successive days.

Diagnostic imaging: This often involves some combination of ultrasound, x-rays (radiographs) and /or computed tomography (CT scan). These are useful for detecting partial obstructions, as well as giving information regarding the shape and architecture of abdominal organs, such as the pancreas, liver and the gut itself.

Diet and antibiotic trials: Antibiotic responsive diarrhoea (in dogs) and food intolerances or allergies (in both dogs and cats) are common causes of chronic diarrhoea. There are no blood tests or biopsies that can effectively diagnose any of these disorders. A diagnosis can therefore only be reached by observing their response to specific antibiotics (antibiotic-responsive diarrhoea) and hypoallergenic, or home prepared food (food intolerances and allergies).

Gut biopsies: Occasionally, it is necessary to obtain biopsies of the lining of the gut in order to diagnose what’s going on. There are two ways in which biopsies can be obtained; via surgery or via endoscopy. Endoscopy involves passing a tube containing a light source connected to a video camera into the stomach and intestines. This allows us to directly visualise the lining of the gut and collect tiny biopsies. Although it requires a general anaesthetic to perform, it is otherwise much less invasive than surgery and has a lower risk of complications. However, the gut is very long and endoscopy cannot visualise the mid-portion of the small intestine. There are occasionally some instances where surgery may be a better option. For example, if the vet suspects the problem involves the mid-portion of the small intestine, where there is an obstruction, or where other organs in the abdomen are involved.

If you’re worried about what could be causing your pet’s chronic diarrhoea, book an appointment with your vet. They will assess your pet, and if they think it may be down to something more serious, you can ask them to refer you to us. Discover more about the referrals process here.

Alternatively, for more information about common illnesses, surgery and treatments for dogs and cats, head on over to our blog.

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Let us know if you have any questions, and our client care team are on hand to answer any questions about our practice, the referrals process and what you can expect.