Diarrhoea in Cats and Dogs

Possible Causes

There are several possible causes of diarrhoea. One way of classifying the diarrhoea is to categorise this as primary gastrointestinal, or extra-gastrointestinal. Primary gastrointestinal diarrhoea indicates that the diarrhoea is caused by an abnormality within the gastrointestinal tract. Primary gastrointestinal diarrhoea can be broken down into further categories such as diet-related, parasites, infectious causes, inflammatory causes, gut obstructions and gut cancers. Extra-gastrointestinal diarrhoea indicates that an abnormality outside the gastrointestinal tract has caused the diarrhoea such as liver or kidney disease. Below is a non-exhaustive list exploring the several possible sources of diarrhoea:









Other primary gastrointestinal causes


Extra-gastrointestinal / non-gastrointestinal causes


Possible Investigations

A complete clinical examination by your veterinarian is the starting point of all diarrhoea investigation in pets. When taking a history, your vet may ask you questions such as whether there has been changes to your pet's diet recently, if there is any changes to their appetite or whether your pet is currently on any ongoing medications etc. If you have photos of your pet's diarrhoea and/or a stool sample, do bring these along to the consultation as it may help assist with the investigation. Apart from the routine physical exam, your vet may also conduct a rectal exam. After your veterinarian has fully evaluated your pet, they may recommend one or a combination of these interventions and/or investigations:

  1. Diet trial - e.g. prescription intestinal diets; hypoallergenic diets
  2. Stool analysis - e.g. microscopic examination for parasites; bacterial culture
  3. Blood tests - e.g. haematology, biochemistry (organ function check), pancreatic function
  4. Advanced diagnostics - e.g. trypin-like immunoreactivity, abdominal ultrasound
  5. Intestinal biopsy
  6. Referral to a specialist


As each pet is unique and every patient is different, your veterinarian will tailor a specific investigation and treatment plan for your pet. If you are concerned about your pet's diarrhoea, please do not hesitate to phone us at (06) 358 8675 to book an appointment for your pet to be checked over by one of our veterinarians. 


Published by Cahill Animal Hospital on 23 April 2016

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