Pet Diarrhea

Pet Diarrhea is a common condition in which there is excess water in the stool due to either the colon’s inability to absorb water as it travels through the intestines or due to the excess secretion of water by the large intestine.

Diarrhea may be either acute (one or more episodes of diarrhea lasting less than 14 days) or chronic (lasting more than 14 days or intermittent over 3-4 weeks).

For dogs, many cases of acute diarrhea can be attributed to a dietary indiscretion, which is less often the case for cats. Cats, in fact, are more likely to have cases of chronic diarrhea.

Diarrhea may be a clinical sign of an intestinal problem or a disorder not involving the intestines.


Veterinarians use fecal scoring scales in order to standardize their assessment of a pet’s stool. One of the common fecal scoring charts uses a 7-point scale. A score of 1 is a very hard and dry stool while a score of 7 is watery diarrhea. A score of 2 or 3 is considered normal.

Fecal scoring chart
(Photo credit: Purina ProPlan Veterinary Diets)

Possible Causes

There are many reasons why dogs have diarrhea. Some of the more common causes are:

Bacterial infection Salmonella is a type of bacteria that can cause inflammation of the intestines. Campylobacter is a type of bacteria that can cause gastroenteritis, or inflammation of the gastrointestinal tract.

Blockage or obstruction of the gastrointestinal tract Blockage or obstruction is an emergency condition that can be caused by a foreign body, folding of the intestines, bloat, or constipation. Common signs of GI obstruction include pain, vomiting, and diarrhea.

Cancer or tumor Cancer is a disease in which abnormal cells grow and reproduce, often in a mass called a tumor. These abnormal cells have the ability to spread to surrounding tissues or other areas in the body.

Diet Food intolerance or allergy occurs when substances that are inhaled, ingested, or absorbed into the body, stimulate the immune system, resulting in inflammation. Pets can have allergies to substances in the air or in food. Food poisoning can be the result of food and water becoming contaminated with bacteria such as Salmonella, Campylobacter and E coli.

Drug-induced Antibiotics are a common cause.

Exocrine pancreatic insufficiency (EPI) EPI is caused by an insufficient secretion of the digestive enzymes by the pancreas. This can lead to an inability to digest nutrients properly, leading to diarrhea.

Fungal infection Fungal infections, such as Histoplasmosis in dogs, can infect multiple organs, such as the lungs, intestines, lymph nodes, liver, spleen, and bone marrow.

Hemorrhagic gastroenteritis (HGE) HGE is a life-threatening disease characterized by a large volume of bloody diarrhea and vomiting. This is often accompanied by hemoconcentration, or a decreased volume of plasma to red blood cells in the blood. It is not contagious and is typically seen in small dogs, such as Yorkshire terriers, Miniature pinschers, Miniature schnauzers, Miniature poodles, and Maltese.

Hyperthyroidism Hyperthyroidism is when the thyroid gland, which controls metabolism, is overactive and leads to an increased level of thyroid hormones.

Inflammatory bowel disease (IBD) is characterized by clinical signs such as vomiting, diarrhea, and weight loss.

Intestinal parasites Parasites in the stomach or intestines can be a cause of diarrhea or other clinical signs in pets.

Kidney disease is the decreased ability for the kidneys to filter waste products from the blood.

Liver disease The liver is responsible for filtering toxins from the body. Liver failure is the inability of the liver to function properly.

Viral infection Canine parvovirus, feline panleukopenia, canine distemper virus, feline infectious peritonitis (FIP) can also cause diarrhea. These diseases are highly contagious and can be life threatening. Immediate veterinary care is recommended.


If your dog or cat is healthy and showing no other signs, you can take a “wait-and-see” approach to allow the digestive system to rest. Withhold food for 24 hours and restrict water to small drinks every few hours. Offer bland food afterwards, such as boiled, skinless chicken, and white rice.

  • Puppies and kittens with diarrhea should see a veterinarian immediately.
  • Successful management of diarrhea requires treatment of the underlying condition or disease.
  • Your veterinarian may prescribe certain treatments depending on the underlying cause. These include de-wormers, antibiotics, vitamin or enzyme supplementation, steroids, or a diet change.

If your pet has diarrhea lasting over 24 hours, or is showing additional clinical signs such as vomiting, fever, blood in the stool, distress, lethargy, decreased appetite, or weight loss, seek veterinary care and bring a stool sample for testing.


In many cases, diarrhea can be prevented. Feed your pet a consistent diet, limit rich foods, and keep trash away from curious pets. Your pet should also get the recommended vaccinations according to your veterinarian and should also be tested annually for intestinal parasites.

By The Animal Medical Center