Chronic Diarrhoea in Pets

Written by Shula Berg BVSc CertAVP(GSAS) GPAdvCert(SASTS) MRCVS
Clinically reviewed by Elizabeth McLennan-Green BVM&S CertAVP(SAM) MRCVS

Table of Contents

- Overview
- Diagnosis
- Treatment
- Outlook

What is chronic diarrhoea?

Diarrhoea is defined as passing looser and/or more frequent stools than normal. This can vary from severe watery diarrhoea, through to soft "cow pat" consistency faeces. Diarrhoea lasting for more than two weeks is considered chronic and unlike an acute bout of diarrhoea, is more likely to be caused by an underlying problem.  

When approaching cases of chronic diarrhoea, the animal's age and breed, any known concurrent disease, and their vaccination and worming status will help to guide investigations. Other important information includes the duration and progression of symptoms, a description of the stools, whether vomiting is present and any recent dietary changes. You may also be asked if your pet has other symptoms, is a scavenger, or could have had access to anything toxic. 

True chronic diarrhoea is usually caused by one of the following: 

  • Infectious (bacterial, viral, parasites) 
  • Inflammatory  
  • Intestinal cancer 
  • Secondary to other systemic disease 
  • Lymphangiectasia (very uncommon)  

Inflammatory conditions are more appropriately termed "chronic enteropathy" and can be further categorised into food-responsive (FRE), antibiotic-responsive (ARE), immunosuppressant-responsive (IRE), or non-responsive (NRE), based on their response to certain treatments. 

Food responsive enteropathy is the most common, and has the best prognosis, as it can be managed using a prescription diet. Non-responsive enteropathy is very uncommon but carries a guarded prognosis as it is extremely challenging to treat these patients. 

What tests are used to diagnose diarrhoea in pets? 

A thorough clinical exam and history taking is always the first step in diagnosis. Further testing will then be required, including some or all the following: 

General Blood Tests 

These are used to provide an overview of organ health as well as checking protein levels (often low with intestinal disease) and screening for pancreatitis. If results suggest a systemic disease is present, more directed blood tests may be required. 

Intestinal-Specific Blood Tests 

Measurement of three specific parameters, known as folate, TLI and B12, provide more precise information about intestinal function and nutrient absorption. 

Faecal Analysis 

This tests for certain parasites and infections such as E. coli, campylobacter and salmonella. Samples are often collected daily for three days to increase the likelihood of findings, as some parasites shed intermittently. 


Urinalysis helps assess organ function. It is especially important if protein levels are low, to confirm that this loss is through the intestines and not the kidneys. 


Ultrasound can be used to assess the structure of the intestines and examine other organs. X-rays of the chest and abdomen may also be recommended. 


Ultimately, endoscopic or surgical biopsies of the intestines may be required for diagnosis, especially to differentiate between severe inflammatory disease and cancerous changes. It is not without risk, so is not advisable for every patient, especially if protein levels are low as these are essential for healing. 

How is chronic diarrhoea treated? 

Treatment depends largely on the results of investigations. If parasites or bacterial infections are identified these have specific treatments, usually followed up with repeat faecal testing to confirm the problem has resolved. Any underlying disease identified should be treated first, as this may lead to resolution of the diarrhoea. 

Chronic enteropathy is often more challenging to treat, and since enteropathies are sub-classified by their response to treatment this makes up an important part of the diagnostic pathway. 

Diet Trial 

A prescription exclusion diet is used to diagnose and manage food responsive enteropathy. Since FRE is the most common chronic enteropathy, all patients should be placed on a diet trial. This typically lasts for 4-6 weeks but improvement may be seen as early as 2 weeks.


If there is no response to a diet trial, a 4–6-week course of antibiotics may be used to rule out antibiotic responsive enteropathy. Given the very real risks of antibiotic resistance to both human and animal health, this is not recommended as a first step in most cases. 


Ideally, immunosuppressive medication is prescribed for a specific diagnosis following intestinal biopsy. This is not always possible, so immunosuppressive treatment, such as steroids, may be prescribed to help manage symptoms. Steroids may also be used as palliative treatment for intestinal cancers. 

B12 Supplementation 

If blood tests show that B12 is low, supplementation is advisable. Low B12 is a side effect of intestinal disease, not a cause, but supplementation may help symptoms. 

Parasite Treatment 

Even if faecal analysis is negative, treatment with a specific drug called fenbendazole may be advised alongside other treatment to cover for protozoal infections. 

Inherently some dogs presenting with chronic diarrhoea are much sicker than others. For dogs who are in good general health, it is recommended to follow the treatment pathway described. For dogs who are moderately to severely unwell at presentation, it may be more appropriate to start multiple treatments, and gradually reduce these to decide a long-term treatment plan. Your vet will advise if this is appropriate for your pet. 

What is the outlook for pets with chronic diarrhoea? 

The prognosis for chronic diarrhoea is variable, depending on the cause. Except for parasitic infection, most conditions are lifelong, and must be managed rather than cured. Diagnosing and treating chronic diarrhoea is a slow process, with no overnight cures. The longer that diarrhoea has been going on, the more secondary changes and chronic inflammation will be present in the intestines. Even if the root cause is treated it may take some time before patients return to passing normal, fully formed stool at a normal frequency. Keeping a stool diary during treatment can be very helpful to identify improvements in consistency or frequency of toilet habits over longer periods. 

Pets who have significant weight loss, very low protein levels, and/or very low B12 levels at diagnosis have a more guarded prognosis. For some pets, it is not possible to control symptoms completely, while for others they need high doses of immunosuppressants and the side effects of these must be weighed against the benefits. Some conditions, such as intestinal cancers, are unfortunately not curable though palliative treatment may be appropriate. Pets who are systemically well and respond to a diet trial can usually be managed very successfully long-term. 


Please note that the content made available on this webpage is for general information purposes only. Whilst we try to ensure that at the time of writing all material is up to date and reflects industry standards, we make no representation, warranties or guarantees that the information made available is up to date, accurate or complete. Any reliance placed by yourselves is done so at your own risk.

Page last reviewed: 16th January 2024
Next review due: 16th January 2026