Help! My Cat Has Diarrhoea

Updated April 13, 2021

There is a good reason why I had written 500 pet health articles before broaching the subject of diarrhoea in cats. It can be extremely frustrating. There is also a lack of good quality information for cat owners.

First a description, then a logical treatment plan.

Types of Cat Diarrhoea

Vets separate cat diarrhoea using two key differences: location and timeframe.

  • Small bowel diarrhoea or enteritis is the more common location. Signs are soft, runny or watery poop, often associated with weight loss and a poor appetite.
  • Large bowel diarrhoea or colitis is not associated with weight loss or a loose stool. Signs are pain when toileting, needing to go more often, and the presence of mucus or blood.

Many cases show a bit of each. Both can be either:

  • Acute, meaning rapid in onset and only lasting a few days, or
  • Chronic, meaning lasting for two weeks or more

It’s this latter distinction that’s most important, as the two have very different origins. I’ll discuss each in turn.

Causes of Acute Feline Diarrhoea

Reasons why a cat might suddenly get diarrhoea include:

  • Diet change, especially if carried out too quickly
  • Feeding inappropriate foods like milk
  • Cats eating prey like birds, mice or even insects
  • Bacterial infections e.g. Salmonella
  • Viral infections e.g. parvovirus (not the dog one!), coronavirus (not the human one!)

Treatment in an otherwise healthy cat can be supportive, such as a bland diet of boiled chicken and access to their preferred type of water.

Many times we never need to know the cause because it gets better quickly. Other times, you will need to see the vet, especially if there are other signs of illness or the diarrhoea persists for more than 24 hours.

In a kitten with loose stools who is otherwise healthy, the first thing I will try is changing them from cheaper supermarket foods onto premium diets. It’s surprising how often this works.

Causes of Chronic Feline Diarrhoea

Once cat diarrhoea persists, there is a whole different set of causes. These include:

Diagnosis is a process of elimination. Therefore we recommend running these tests in the following order:

  1. Blood testing to detect problems of the liver, kidney, pancreas and thyroid
  2. Faecal testing to detect the infectious causes, especially in young or rescue cats
  3. Ultrasound to detect many tumours

One thing that all cat owners need to know is that most of the time these tests will be negative. Occasionally that might tempt us to skip to the next step but we need to keep in mind what we’ve missed if we do.

Once we have eliminated the above conditions, we are left with a condition we call chronic enteropathy or CE.

Investigation of Chronic Enteropathy

Now finally we are down to only three common conditions. These are:

  • Food Responsive Enteropathy (FRE)
  • Steroid Responsive Disease (SRD)
  • Small Cell Lymphoma

The observant among you might notice that I haven’t mentioned IBD. That’s because IBD overlaps with both FRE and SRD, which are more practical and workable descriptions.

Now the plan will be the following three tests:

  • Dietary trials
  • Immunosuppressive trials
  • Intestinal biopsies

The order in which we do these will depend on the health of your cat. For example, a severely unwell cat is probably best stabilised and having biopsies done before things get worse. A mildly affected cat can probably go through the tests in the order above, stopping when improvement occurs.

Food Trials

Around 60% of cats with chronic enteropathy will respond to nutritional management. These odds are so good that even if the first diet trial fails, it’s worth trying a different one before moving on. In fact, if there’s time I will try to do three:

A response to the new food is often seen within two weeks.

Food allergy or intolerance usually develops over a long period. A common mistake is to assume that it can’t be a food problem because the diet hasn’t changed.

Medication Trials

A failure to respond to a food trial will lead us to either a medication trial or biopsy, depending on the urgency of the case and owner preference. The use of prednisolone has lower rates of success than food but is the logical next step for most. It has significant side-effects, that you can read about at the link.

Cats that respond to prednisolone are probably the ones that have IBD (often also called lymphocytic‐plasmacytic enteropathy). Sometimes we get the best results by continuing a hydrolysed diet during the medication trial.

Intestinal Biopsy

Small cell lymphoma in cats is just as common as IBD, but the only way to diagnose it is via tissue samples. These can be collected endoscopically but are more accurate if done via abdominal surgery. The invasive nature of the procedure explains why we often delay biopsies, but we can make the mistake of waiting too long.

If a cat gets too unwell, they may not recover from the surgery. Also, small cell lymphoma has a good treatment but it takes time to work.

Additional Therapies

All cats wth CE should also either have their serum vitamin B12 checked or receive regular B12 injections. Vitamin B12 levels are affected by intestinal disease, and the deficiency then worsens the problem.

More than once I have seen cats for whom everything was done right, but who only got better when B12 was given. The response is usually rapid.

There is no evidence for the use of probiotics or prebiotics. However, I have had good responses to their use in some cases, and they are well worth trying.

Lastly, there is much talk of the use of fibre. I have stopped recommending this due to poor results, but you are welcome to try.

In summary, the best attitude to feline diarrhoea is to be logical and follow the steps above without excessive delay. I hope that you, after reading this, find a simpler and earlier solution. However, I also hope you can see that there’s a lot of reason for optimism whatever the diagnosis.

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By Andrew Spanner BVSc(Hons) MVetStud, a vet in Adelaide, Australia. Meet his team here. The information provided here is not intended to be used as a substitute for going to the vet. If your pet is unwell, please seek veterinary attention.