From Cat

There are numerous causes to diarrhoea in cats.

When diarrhoea persists as a chronic illness (more than 7-10 days), despite treatment with anthelmintics and antibiotics, chronic diarrhoea then becomes part of a syndrome known as irritable bowel disease (IBD). An umbrella term for any chronic diarrhoea in cats that is non-responsive to standard treatment, IBD is relatively common in purebred cats, with certain breed predilection for Ragdoll, Siamese and Burmese.

Clinical signs

The clinical signs of diarrhoea vary with the location of the inflammatory process; duodenal and gastric lesions usually present as vomiting and weight loss while small and large intestinal lesions present as diarrhoea and/or weight loss. There are also some cats in which the inflammatory response extends beyond the intestinal tract and affects the liver (+/- gallbladder) and pancreas. This is fondly termed 'triaditis'.

Area affected Symptoms
Small intestine +/- vomiting, normal frequency of motions, little pain associated, smelly, may be black if bleeding involved, often watery
Large intestine Frequent and 'urgent', usually cow-pat appearance, bright-red if bleeding involved
Triaditis (small intestine, liver and pancreas) vomiting, and symptoms of small intestinal involvement (i.e. watery and smelly +/- black blood)


There are many causes of diarrhoea in cats, including small and large intestine and combinations:

Causes of small intestinal diarrhoea (in order of likelihood)
Protozoa - Isospora spp, Sarcocystis spp, Besnoitia spp, Hammondia hammondi, Toxoplasma spp, Giardia spp, Tritrichomonas spp, Entamoeba histolytica, Balantidium coli, Cryptosporidium spp
Worms - round worms (Toxascaris leonina and Toxocara cati), tapeworms (Dipylidium spp), stomach worm (Ollulanus tricuspis)
Hormonal - Hyperthyroidism, End stage uraemia
Nutritional - allergy to protein, preservatives (#220-228 are sulphites), gluten (dry food)
Lymphangiectasia, Antibiotic responsive diarrhea/bacterial flora imbalances, 'Short bowel syndrome'
Chronic pancreatitis, Exocrine pancreatic insufficiency
Bacteria - Salmonella spp, Campylobacter spp, E. coli., Clostridium spp, Helicobacter spp, Mycobacterium spp, Shigella spp, Anaerobiospirillum spp, Histoplasma spp, Pythium spp,
Viruses - rotavirus, Feline leukemia virus (FeLV), Feline Aids (FIV), Coronavirus (FIP), Feline Panleucopenia, Feline morbillivirus
Fungi - Histoplasma spp, Aspergillus spp, Candida spp, Phycomycetes spp
Cancer - Lymphoma, lymphosarcoma, Pancreatic neoplasia
Causes of large intestinal diarrhoea
Tritrichomonas foetus, Cryptosporidium spp'


Mucosal biopsies collected from the stomach and duodenum via endoscopy, are relatively non-invasive and less expensive than laparoscopy. Unfortunately, mucosal biopsies alone may miss a diagnosis of lymphoma in cats, especially in individuals with intestinal but not gastric involvement. In addition, standard GI endoscopy does not allow evaluation of the jejunum or ileocecocolic junction. Full-thickness biopsies obtained by abdominal exploratory laparotomy or laparoscopy are ideal for diagnosis of IBD and the exclusion of lymphoma, but may allow fine needle aspiration of a lymph node or a focal area of intestinal thickening for a cytological diagnosis of lymphoma. Lack of normal intestinal wall layering suggests nheoplasia and warrants surgical excision or full-thickness biopsies for clients who would pursue chemotherapy for lymphoma.

Serum folate and cobalamin concentrations may also be useful in planning biopsies. Low serum folate is consistent with proximal small intestinal malabsorption. This finding, along with duodenal thickening on ultrasonography, suggests that endoscopy might be adequate to sample the affected area. A decreased serum cobalamin suggests ileal cobalamin malabsorption, either due to infiltrative ileal disease or pancreatic insufficiency.

Abdominal ultrasound can be useful in deciding between endoscopy and full-thickness biopsies. Thickened intestines or mesenteric lymphadenopathy cannot reliably distinguish between more severe IBD and diffuse intestinal lymphoma

Pancreatic insufficiency is rare in cats, but a serum feline trypsin-like immunoreactivity (fTLI) test should be submitted if weight loss and polyphagia are present in a euthyroid, non-diabetic cat. If fTLI is normal, ruling out pancreatic insufficiency, cats with low serum cobalmin concentrations may be best taken to surgery for full thickness biopsies of the duodenum, jejunum and ileum. Because pancreatitis can be present concurrently with IBD, cats with chronic GI signs should also be screened for elevated serum feline pancreatic lipase immunoreactivity (fPLI), especially if the pancreas appears mottled on ultrasound examination or abdominal discomfort is detected on physical examination.

Unfortunately, a long duration of signs (> 1 year) does not rule out lymphoma.


Dietary manipulation is a critical first step in the management of diarrhoea in cats.

Novel protein (elimination) diets are designed to avoid exposure to proteins to which the cat's gut mucosal immune system may have been previously sensitised. Most commercial elimination diets contain a novel protein source, are milk-, corn- and wheat-free, and are highly digestible with a moderate amount of soluble fibre.

Dietary manipulation alone has a fairly high efficacy in treating chronic GI disease in cats, and avoids the side effects associated with immunosuppressive therapy. In fact, up to 50% of referred cats with idiopathic (unknown) GI signs will respond very well to an elimination diet trial, using a home-cooked novel protein source or one of the many commercial elimination diets now available. A commitment to a 4-6 week dietary trial has previously been recommended, which may dissuade some clinicians and owners. However, in most cases, many cats respond in a much shorter time (within 2-3 days), so a shorter dietary trial is acceptable (e.g. 1 week to allow for dietary transition).

An alternative to elimination diets are hydrolysed protein diets (e.g Hill's Z/D Royal Canin Hypoallergenic diet). They minimise the antigenicity of intact dietary protein. Hydrolysed protein diets may be ideal as 'sacrificial diets' during initial induction therapy, while glucocorticoids are used to try to avoid sensitization to any formerly novel intact proteins.

In cats that are not responsive to dietary change, immunosuppressive therapy remains the standard of care, but will hopefully be replaced in future by more specific therapies.

Therapy Uses Dose Side effects
Prednisolone Irritable bowel disease 1-2 mg/kg orally every 12 hrs, then decreasing Diabetes mellitus, gastritis, heart failure
Budesonide Irritable bowel disease 1 mg orally every 24 hrs Can lead to some systemic side effects
Leukeran (Chlorambucil) Irritable bowel disease 2 mg/cat every 48-72 hrs Anorexia, bone marrow suppression, lymphopenia
Cyclosporin Irritable bowel disease Unknown Immunosuppression, anorexia, vomiting
Cobalamin Hypocobalaminemia 250 micrograms SQ every 7 days for 6 weeks None
Barium Gastrointestinal bleeding 5 ml orally every 4 hrs Vomiting, aspiration, anorexia

Probiotics, omega-3 polyunsaturated fatty acids and cobalamin are also strongly recommended as adjuncts to any therapy for IBD.