Why Does My Dog Have Diarrhea?

Let’s talk about poop. Dog poop, to be specific. Diarrhea, the passage of frequent loose stools, is a common problem for dogs. The extensive list of causes ranges from harmless and self-limiting to serious and life-threatening. Ambleside Animal Hospitalbreaks down the most common causes of “the runs” in dogs, and explains when home treatment is OK, and when to call your veterinarian.

Causes of diarrhea in dogs

Changes in your dog’s intestinal environment may lead to inflammation and a decreased ability to absorb nutrients and fluid. This typically leads to varying diarrhea types, depending on which portion of the intestine is affected, and the underlying cause. Here are some of the most common causes of diarrhea in dogs.

Infections and bacterial imbalances — Many types of microorganisms are capable of causing diarrhea in dogs, including:

  • Parasites — Parasites such as roundworms, hookworms, whipworms, giardia, and coccidia frequently infect puppies, and cause diarrhea through intestinal damage.
  • Bacteria — Bacteria such as Salmonella, Clostridium, and E coli may cause diarrhea in some dogs. In others, these bacteria are part of the normal intestinal environment and never cause a problem.
  • Viruses — Parvovirus, distemper, and canine coronavirus (not COVID-19) typically affect young, unvaccinated puppies, and may cause severe diarrhea.
  • Dysbiosis/Antibiotic-Responsive Diarrhea – The gastrointestinal tract has a delicate balance of good and bad bacteria. Diarrhea results when the bad bacteria overgrow, which is called dysbiosis, small intestinal bacterial overgrowth (SIBO), or antibiotic-responsive diarrhea.

Diet-related problems — When your pet consumes non-edible material or table scraps, experiences a quick diet change, or develops a food allergy, diarrhea can result.

  • Foreign body/material — Swallowing pieces of toys, bones, sticks, trash, or other material may cause life-threatening intestinal blockages, or damage the intestinal lining, causing diarrhea.
  • Diet change — Dogs become accustomed to their diets, so abrupt changes cause diarrhea because they cannot digest the new food right away. Diet changes should be gradual, to allow for an adjustment period.
  • Food allergy — Food allergies develop when inflammation causes protein molecules to leak through the gut lining, where the immune system tags them as foreign. Any dog can develop a protein allergy, whose signs include diarrhea or skin problems, at any time.

Primary intestinal diseases — When diarrhea becomes an ongoing or recurring problem, intestinal disease may be suspected. These include:

  • Inflammatory bowel disease (IBD) — IBD is a term for several types of intestinal inflammation caused by a faulty immune system. Chronic diarrhea is common, along with vomiting and weight loss.
  • Lymphangiectasia — Blockage of tiny lymphatic drainage vessels in the intestines causes protein loss and diarrhea in this condition, which may be serious.
  • Cancer — Some cancer types, such as lymphoma, are common in the intestinal tract. Signs include chronic diarrhea, vomiting, and weight loss, and can mimic IBD.

Diarrhea secondary to other diseases — Sometimes diarrhea can result from a problem elsewhere in the body. Conditions include:

  • Pancreatitis — Inflammation of the pancreas may be caused by ingestion of a fatty meal or treat. Signs include vomiting, diarrhea, and lethargy.
  • Exocrine pancreatic insufficiency (EPI) — Your dog’s body needs enzymes produced by the pancreas to break down their food. With EPI, food goes undigested, because the pancreas cannot produce these enzymes. Diarrhea, weight loss, and a ravenous appetite are the result.
  • Liver dysfunction — The liver works closely with the intestines, producing bile to help with digestion. When the liver isn’t working properly, diarrhea may result.
  • Addison’s disease — Addison’s disease, which is caused by a deficiency of stress hormones, has been labeled “The Great Pretender,” because it mimics other diseases. Addison’s may cause repeated episodes of unexplained diarrhea, especially during times of stress.

Miscellaneous — Other common causes of diarrhea in dogs include:

  • Stress — Stress is mediated by hormones, and one of the resulting physical problems can be diarrhea. Stress-induced diarrhea commonly occurs in dogs in boarding kennels and veterinary offices.
  • Physical activity — Exercise is a form of stress on the body, and can induce diarrhea or vomiting in sensitive dogs.
  • NSAID toxicity — Overdose or sensitivity to normal doses of non-steroidal anti-inflammatory drugs (e.g., Rimadyl or Previcox) may cause diarrhea in some dogs.
  • Shock — Heatstroke or a severe allergic reaction may induce shock, a severe restriction of blood flow in the body. Reduced blood flow to the intestines causes diarrhea.

When to treat your dog’s diarrhea at home

If your dog develops diarrhea, but is otherwise eating and acting normally, immediate concern is not warranted. A few days of a “bland diet” usually does the trick for mild cases. A bland diet consists of one part lean chicken, beef, or eggs, combined with three parts rice or potato. Feed small amounts four to six times daily, and then gradually transition back to your dog’s regular diet once their diarrhea stops.

When to visit your veterinarian

For puppies, bring a stool sample to each wellness visit to check for parasites. Adult dogs should have a stool sample checked at least yearly, and remain on heartworm prevention year-round, as these products control intestinal parasites, too.

If your dog develops diarrhea that persists for more than 48 hours, a large amount of blood is present, or they also are vomiting, lethargic, or restless, with a poor appetite, call your veterinarian for an urgent appointment. Be prepared to answer a lot of questions about your dog’s stools, and any additional signs of illness they may be experiencing. Your answers will help your veterinarian narrow down the list of possible causes, and know which tests to order and treatments to start.

Call us to schedule an appointment with your Ambleside Animal Hospital team if your pet is experiencing serious diarrhea, or for your pet’s regular wellness visit and parasite screening.