At a glance
About: Diarrhea is the passage of loose, watery stools. It can be acute (sudden onset) or chronic (lasting longer than two weeks). It can originate from the small or large intestine.
Diagnosis: Baseline tests to evaluate the overall health of your cat, fecal tests, diagnostic imaging and additional tests depending on the veterinarian’s index of suspicion.
Treatment: A bland diet to rest the gastrointestinal tract, supportive care such as fluids, nutritional support and specific treatment depending on the underlying cause.
What is diarrhea?
Diarrhea is an intestinal disturbance characterised by the rapid movement of abnormally loose or watery stools (feces). It is not a disease in itself, but a symptom of an underlying disease or disorder.
Diarrhea can affect the small intestine, the large intestine or both. It may be acute (sudden onset), chronic (over a long period) or intermittent (come and go). There may be an increase in the number of bowel movements, an increased amount of feces or watery feces. Feces may also be yellow and frothy in appearance, be mixed with blood (dysentery) and/or mucus.
- Acute diarrhea has a rapid onset and lasts less than 2 – 3 weeks.
- Chronic diarrhea lasts longer than 2 – 3 weeks.  Blood and or mucous may or may not be present in the feces.
Causes of diarrhea in cats
- Food allergy.
- Food intolerance: Such as lactose in milk.
- Dietary indiscretion: Eating something he shouldn’t have, such as garbage).
- A sudden change in diet.
- Bacterial infection: Salmonellosis, campylobacter, E. coli, tuberculosis, tularaemia.
- Viral infection: FIV, FeLV, panleukopenia, rotavirus, pseudorabies.
- Protozoa infection: Giardia or cryptosporidium.
- Parasitic infection: Liver flukes, parasitic worms such as roundworm and hookworm.
- Histoplasmosis (disseminated): A rare fungal infection that usually affects the lungs, in some cases the infection can spread throughout the body causing several symptoms including diarrhea.
- Colitis: Inflammation of the colon.
- Inflammatory bowel disease: A group of conditions in which different types of inflammatory cells invade the intestines.
- Pancreatitis: Inflammation of the pancreas.
- Hyperthyroidism: A benign hormone-secreting tumour of the thyroid gland.
- Kidney disease: Chronic which is slow and progressive and seen most often in middle-aged to senior cats or acute which is sudden onset.
- Liver disease: Can be due to ingestion of toxins, congenital disorders, infection or inflammation.
- Complications of diabetes.
- Blockage: Hairball or foreign object.
- Certain medications: Antibiotics, chemotherapy, antihistamines, steroids.
- Exocrine pancreatic insufficiency: Failure of the pancreas to secrete appropriate levels of pancreatic enzymes which are necessary for the digestion of food.
- Heinz body anemia: A type of anemia (reduced number of red blood cells) characterised by the presence of Heinz bodies on the red blood cells which leads to their destruction by the cat’s immune system.
- Poisoning: Zinc, ibuprofen, uremic, antifreeze or other.
- Insect/spider bites or sting.
- Anaphylaxis: An acute allergic reaction.
- Malabsorption: An inability of the digestive system to absorb nutrients as it should, there are several underlying causes of this including inflammatory bowel disease, exocrine pancreatic insufficiency, blockage, bacterial overgrowth, parasites, certain cancers.
Related article: Cat with diarrhea but acting normal: what to do.
Symptoms can vary depending on the underlying cause and if the small or large intestine is involved.
- Small intestine diarrhea: Volume is increased, frequency 2-3 times normal, no mucus, urgency may be normal to mildly increased.  Cats with chronic small intestinal diarrhea lose weight and body condition as they are not absorbing nutrients.
- Large intestine diarrhea: Volume is normal to decreased, mucus and blood may be present, the urgency is increased, and frequency is more than five times normal. 
Other symptoms may also occur depending on the underlying cause of diarrhea and may include:
- Anorexia (loss of appetite)
- Increased thirst, due to fluid loss
- Flatulence (farting)
- Abdominal pain
- Blood, fat or mucus in the stool
- Weight loss
- Increased urgency to defecate
- Defecating outside the litter tray
Does a cat with diarrhea need to see a veterinarian?
Mild cases of diarrhea, lasting 24 hours or less, where your cat seems to be otherwise well can be watched carefully at home. As a precaution, take away your cat’s food for 12-24 hours to see if the problem resolves. Leave water out at this time. See a veterinarian if the following symptoms are present:
- Diarrhea (may contain blood)
- If he appears to be in pain, such as hunched over or a tucked up belly
- Kittens under 12 months of age, or senior cats
- Pale gums
Identifying a cat with diarrhea in a multi-cat household:
When there’s more than one cat in the home, it can be challenging to identify the cat with diarrhea, unless you watch them in the litter tray.
An easy way to determine which cat has diarrhea is to use a box of crayons (Crayola claim theirs are non-toxic to humans, so I would give this brand a try if you can). Use a pencil sharpener or cheese grater, to make some crayon shavings; each cat has his or her own colour. Add one teaspoon of shavings to each cat’s food. This means that the cats must eat separately and any uneaten food removed. The shavings will pass harmlessly through the cat and out via the feces.
The veterinarian will perform a physical examination of your cat and ask you some questions to determine if the diarrhea is acute or chronic? If there have been any changes to your cat’s diet, possible exposure to toxins, or other symptoms you may have noticed.
The type and colour of diarrhea, along with accompanying symptoms as well as the cat’s age can help your veterinarian narrow down a cause. For example, a kitten is more likely to have eaten something he shouldn’t; a senior cat is at increased risk of hyperthyroidism or cancer.
- Complete blood count: A blood test that counts the different cells in the blood and may reveal anemia (low red blood cells) and/or increased white blood cell count (infection or inflammation).
- Biochemical profile: Performed on the clear/fluid portion of the blood the biochemical profile measures liver, kidney and pancreatic function as well as electrolytes and enzymes.
- Urinalysis: A urine test to evaluate kidney function and level of hydration.
- Multiple fecal examination tests: Fecal flotation, cytology, smear, zinc sulfate, culture and sensitivity to determine if the cause is parasitic, bacterial, or protozoal.
- FIV and FeLV blood tests.
- Thyroid test: To evaluate for hyperthyroidism in middle-aged to older cats.
- X-rays: To check for blockage, foreign body or tumour and assess the internal organs.
- Ultrasound: To evaluate for cancer or intestinal blockage and assess the internal organs.
- Endoscopy and biopsy: An endoscope is a thin, flexible tube with a light and camera which enables your veterinarian to see the small intestines and stomach. A tissue sample (biopsy) can be taken at this time.
- Colonoscopy and biopsy: Similar to the endoscopy, a thin, flexible tube is passed into the rectum and colon to view the structures and take a biopsy if necessary.
The goal of treatment is to treat the underlying cause as well as manage symptoms and provide supportive care.
Rest the gastrointestinal tract: The veterinarian may recommend that you withhold food if the cat seems otherwise fit and well, water should still be provided. Food can be re-introduced after a day; this will usually be bland to rest the gastrointestinal tract.
Dietary therapy: Feed a highly-digestible diet with low to moderate fat, moderate protein and carbohydrates or a home-made diet of boiled chicken breast and rice.
Hills I/D may be recommended during recovery, this food is designed for gastrointestinal disorders and is highly digestible and low in fat.
Probiotics: Lactobacillus, a type of friendly bacteria residing in the intestinal tract of mammals (including cats), these bacteria protect the body against pathogenic (harmful) bacteria can help, especially if the cat has been on a recent course of antibiotics. Giving lactobacillus milk can replace lost helpful bacteria.
Note: Unlike milk, plain yoghurt contains much lower levels of lactose.
Supportive care: Fluid therapy if the cat is dehydrated and correct electrolyte and acid-base imbalances.
Specific therapy: This will depend on the underlying cause but may include antibiotics, antiparasitics, surgery, food trials (switch to a hypoallergenic diet to see if symptoms improve), vitamin B12 injection, and medical management for cats who have ingested toxins.
If the diarrhea is mild and your cat otherwise seems well, you may wish to try treating it at home for a day or so, if symptoms persist or you notice other symptoms, seek veterinary attention.
Pumpkin: Either cooked (steamed or boiled) or canned (not the pie filler type) may be of help in relieving diarrhea. Add 1 tablespoon to food, or plain, if the cat will eat it.
Never give anti-diarrheal medications unless prescribed by a veterinarian; most human medications are extremely toxic to cats.
Helpful articles about cat diarrhea:
Cat with diarrhea but acting normal: what to do.
Home remedies for cats with diarrhea
Bland diets for cats with diarrhea