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20th August 2018


The normal faeces (stools) that a cat passes are brown in colour and well formed. If a cat is suffering from diarrhoea, the faecal consistency changes to become soft, liquid, or even watery. The colour may also change to become lighter or darker than normal.

In some cases, other signs may be observed – there may be fresh blood or mucus in the faeces, the cat may be producing a greater volume of faeces than normal, and there may be an increased frequency of defecation and/or straining to pass faeces. Some cats will also develop vomiting along with their diarrhoea, and perhaps other signs such as loss of appetite and lethargy.

It is always worth having your cat checked by a vet whenever diarrhoea is severe, accompanied by other signs, or if the diarrhoea persists for more than a few days. Although blood in the faeces may appear alarming, unless there is a very large amount this does not require emergency attention, but your cat should be checked by your vet ideally within a day or two.

Although not pleasant, it is worthwhile taking careful note of your cat’s toilet habits and noting the nature of the diarrhoea, frequency of the diarrhoea, whether there is any straining, blood or mucus present etc. as these are all things that will help your vet narrow down the potential underlying causes.

Causes of diarrhoea

In general terms diarrhoea can be caused either by a disease of the intestinal tract itself (primary intestinal disease), or less commonly by a disease affecting another organ (systemic disease) that in turn is affecting the intestine (eg, liver or kidney disease). The majority of cases of diarrhoea are due to primary intestinal disease.

Many cases of diarrhoea are mild, short-lived (last for only a few days), and spontaneously resolve. In many of these cases a specific underlying disease is never diagnosed and cats may get better by themselves or respond to symptomatic and supportive treatment (see later). In other cases, especially where the diarrhoea is severe or prolonged, investigations may need to be done to determine the underlying cause and appropriate treatment.

Some of the common causes of diarrhoea include:

  • Diet – a sudden change in diet or the introduction of a new food (or hunting/scavenging food outside) is a common cause of mild and transient diarrhoea. Often this settles down as the intestine adapts to the new diet. This is particularly common in younger cats and when hand-rearing or weaning a kitten the use of foods not designed for the cat, or overfeeding, are common mistakes which can lead to diarrhoea. In some cases, older cats (especially those that go outside) may consume spoiled (decayed) meat that can cause diarrhoea. Some cats may not be able to tolerate certain foods, and in these cases the diarrhoea will not resolve until the diet has been changed – a good example is that many cats are intolerant of the lactose (sugar) present in milk.
  • Infectious causes – a wide variety of different infectious agents can cause diarrhoea in cats. These include viruses (often causing mild and transient diarrhoea, although some viruses such as feline parvovirus and feline leukaemia virus can cause severe life-threatening disease), bacteria (such as Salmonella and Campylobacter) and parasites (such as GiardiaTritrichomonas and coccidia). Infectious agents will frequently affect more than one cat in a household, and are more common in younger cats.
  • Dietary allergy – although not particularly common, some cats may develop an allergy (hypersensitivity) to something (usually a protein) present in the diet. This usually happens after a food has been fed over a long period of time rather than being associated with a recent change in diet.
  • Inflammatory bowel disease – this is a complex group of disorders that result in chronic (long-term) persistent or intermittent diarrhoea and/or vomiting in cats. It is a relatively common causes of chronic diarrhoea and is associated with marked inflammation in the wall of the intestine.
  • Intestinal tumours – these are generally more common in older cats. The two most common tumours in the intestine are lymphoma and adenocarcinoma. They can cause disease and clinical signs by interfering with the normal absorption of food and also by causing partial obstruction of the intestine.
  • Benign polyps and growths – although uncommon, occasionally benign growths or polyps can develop in the intestine and often cause disease through gradual partial obstruction to the passage of food.
  • Pancreatic insufficiency – although this is an important cause of diarrhoea in dogs, pancreatic insufficiency is rare in cats. However, the pancreas is responsible for producing important digestive enzymes and when these are not produced (pancreatic insufficiency) diarrhoea will result as food cannot be properly digested.
  • Vitamin B12 deficiency – although not fully understood, there is an important relationship between chronic diarrhoea in cats and vitamin B12 (cobalamin) deficiency. These cats may need to have vitamin B12 replacement therapy before their diarrhoea will resolve.
  • Systemic diseases – these are an important consideration, although are a less common cause of diarrhoea than primary intestinal disease. Systemic diseases that can affect the intestine and cause diarrhoea include: hyperthyroidism (overactive thyroid gland)liver disease and kidney disease

Signs of diarrhoea

Diarrhoea can vary greatly between cats in its severity, depending partly on the underlying cause. The region of the intestine affected will also determine some of the clinical signs so, for example, if the large bowel (colon) is affected then common signs include straining, increased frequency and passing mucus and sometime some fresh blood with faeces.

If cats do not use a litter tray indoors, it can sometimes be difficult to know whether they have diarrhoea and other signs such as weight loss may be more obvious. However, if the diarrhoea is severe, even outdoor cats may start having accidents in the house and there may also be soft faeces stuck to the fur under the tail.

Diagnostic tests

Your vet will first examine your cat and talk with you about what has been going on, before deciding if further tests are necessary. One of the difficulties is that there are so many different potential causes of diarrhoea, in some cases quite extensive investigations may be needed to determine the cause.

If the diarrhoea has developed recently, is relatively mild, and the cat is still bright and alert, your vet may simply suggest symptomatic treatment to see if the problem resolves. If not, or if the diarrhoea is more serious, further investigations may be warranted. Vets will try to do these investigations in a logical and structured way so that potential causes of the diarrhoea are not missed. Investigations may include:

  • Dietary change (see below under treatment).
  • Blood and urine tests to rule out systemic disease and things like pancreatic insufficiency and low vitamin B12 levels.
  • Examination of faecal samples – these can be assessed for the presence of parasites (often 3 different faecal samples are collected for this so that parasites are not overlooked), and to culture for the presence of potentially harmful bacteria.
  • Radiographs (X-rays) and ultrasound are often used to examine the gastrointestinal tract and to detect physical abnormalities.
  • Endoscopy – this is where a small medical camera is passed into the intestine (either through the mouth and/or through the anus) under general anaesthesia, so that the lining of the intestine can be examined and biopsies can be collected. This can be valuable, especially where tumours, polyps or inflammatory bowel disease are suspected.
  • Exploratory survey – this is sometimes done as an alternative to endoscopy or if endoscopy has failed to provide an answer. It allows all of the intestines to be examined (along with organs such as the liver and pancreas) and provides an excellent way of getting biopsies from different parts of the intestine.


Treatment of diarrhoea can be either specific or supportive. Most cases of moderate to severe diarrhoea will need some form of supportive treatment but specific treatment requires identifying the underlying cause and targeting the treatment at this.

Supportive therapy

Most cats with diarrhoea that has persisted for any length of time will benefit from supportive therapy. This may include:

  • ‘Resting the gut’ – in cases of acute (sudden and recent onset) diarrhoea, simply withholding food for a short period (24 hours) may help things to settle down. Unless otherwise indicated though, a cat should not be deprived of food for longer than 24 hours as this could be detrimental.
  • Dietary therapy – switching to a simple, highly digestible diet is often very helpful in managing diarrhoea irrespective of the underlying cause. A home-cooked diet of chicken or fish with a little white rice is suitable in the short-term, but for longer-term management a more balanced diet is preferable and your vet will be able to recommend a number of options. In addition, a diet trail is an important part of the investigation of persistent diarrhoea to rule out dietary intolerance or dietary allergies. In these cases, special diets available from your vet are often used.
  • Probiotics – probiotics are live bacteria that can be given with food. They can sometimes help in the management of diarrhoea by improving intestine health, but will not always be indicated. Some probiotics have been specifically developed for use in dogs and cats.
  • Fluid intake – with more severe diarrhoea it is possible for cats to become dehydrated, so attention may be given to fluid intake and your vet may even suggest you encourage your cat to drink an appropriate electrolyte solution rather than just plain water to help with this.

Specific therapy

Specific therapies will depend on the underlying cause of the diarrhoea, but these may include:

  • Anti-bacterial and anti-parasitic drugs – if infectious agents are identified then specific drugs may be available to treat your cat and eliminate them. However, antibiotics should never be used indiscriminately as they can cause exacerbation of diarrhoea, interfere with other investigations, and unnecessary use of antibiotics simply promotes bacterial resistance.
  • Anti-inflammatory and immunosuppressive drugs – these are often used in the management of inflammatory bowel disease.
  • Surgery and/or chemotherapeutic drugs – these can be useful in the management of intestinal neoplasia.
  • Vitamin B12 – weekly injections of vitamin B12 are generally used when B12 deficiency has been diagnosed.


The prognosis depends on the cause of the diarrhoea – diseases which are easily managed with diet and/or drugs carry a good prognosis, and many cases will completely resolve with appropriate therapy. In other cases, ongoing therapy may be required.

In all cats, diagnosing the underlying cause of persistent diarrhoea early will help prevent long-term changes in the gut which may be irreversible.

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