Dog Diarrhea Causes

Dog diarrhea causes range from being mild and transient to being serious and potentially life-threatening.

In fact, diarrhea isn't so much an illness in itself as a symptom of some other ailment or condition. That condition can be as mild as a change in diet or as serious as a viral infection or autoimmune disease.

Small Intestine vs. Large Intestine Inflammation

Dog diarrhea can be caused by inflammation of the small intestine, the large intestine, or both. Your dog's symptoms provide clues to the type of diarrhea he is experiencing.

• Increased stool volume.
• Stools are very loose and may contain undigested fats.
• Frequency of bowel movements is normal or slightly increased.
• No increased urgency to defecate.
• Little if any straining while defecating.
• If there's blood, it will be dark, not bright red.
• Dog may also experience vomiting or abdominal pain.
• Usually accompanied by weight loss.

• Small or normal stool volume.
• Stools are loose or semi-formed, often "pudding-like."
• Stools typically contain lots of mucus.
• Dog strains to defecate, often tries to eliminate several times.
• Frequency of bowel movements is usually increased.
• Increased urgency to defecate is common.
• If there's blood, it will be bright red or slightly rust-colored.

Acute vs. Chronic Forms of Dog Diarrhea

We also distinguish between acute and chronic forms of diarrhea, the primary difference being one of duration.

Acute diarrhea can last anywhere from a couple of hours to a couple of weeks.

Most cases of acute canine diarrhea resolve themselves without the need for veterinary care, but there are a number of potentially very serious acute dog diarrhea causes that require veterinary attention, and the sooner, the better.

When symptoms persist longer than two or three weeks, we are looking at a case of chronic diarrhea. Depending on the cause, chronic diarrhea can be difficult to get under control.

While eliminating the cause of chronic dog diarrhea is obviously preferable to merely treating the symptoms, we often have to settle for the latter because, in a growing number of cases, the culprit is an autoimmune disorder that can be treated but not cured.

Dog Diarrhea Causes - Acute

Changes in Diet: Dogs who've been eating the same food for a long time can experience diarrhea if the formula suddenly changes or they are switched to a new food. That's why it's a good idea to introduce new foods gradually if your dog is not used to variety. Dogs who regularly eat a wide variety of foods are far less likely to experience digestive upsets when introduced to a food they haven't encountered before.

Certain Foods: Large amounts of certain foods can cause diarrhea in dogs even if there's nothing wrong with the food in terms of contamination. Prime culprits include organ meats (particularly livers and kidneys), oils and fats (including fatty meats), dairy products (stick to yogurt and cottage cheese because they contain very little lactose), and raw fruit.

That doesn't mean these foods should be avoided. On the contrary, many of these foods are very healthy; however, they are best fed in small amounts and introduced slowly.

Low quality dog foods with poor digestibility are also contenders for causing diarrhea, as the digestive tract is overwhelmed by substances it can't use.

Poisons: Some poisons and plant toxins can cause acute diarrhea, but diarrhea usually won't be the only symptom in those cases. If you suspect that your dog has ingested poison of some type, it's critical to rush her to the vet right away. And be sure to store insecticides, household cleaners, and other toxic chemicals where your dog can't reach them.

Bacterial Infections: Healthy dogs are able to handle large bacteria loads, but in times of sickness or stress, bacteria such as Clostridium perfringens, Escherichia coli, and Salmonella can gain the upper hand and wreak havoc. Even healthy dogs may, on occasion, encounter more pathogenic bacteria than they can handle, and acute as well as chronic diarrhea is a typical symptom of such bacterial overgrowth.

Viral Infections: A number of canine viruses have diarrhea as a symptom. The two most serious are canine parvovirus and canine distemper virus. These viruses are frequently fatal in puppies, so vaccinations are strongly recommended.

Mold Contamination: Bacteria and protozoa aren't the only microorganisms that can contaminate food or water. Molds can grow in food as well as water bowls, and there have been a number of pet food recalls due to mold contamination.

Medications and Supplements: Several drugs your veterinarian may prescribe can cause diarrhea in dogs. Antibiotics top the list of drug-induced dog diarrhea causes. Long-term antibiotic therapy, in particular, has the potential to severely disrupt your dog's intestinal microbial balance. To replenish the beneficial bacteria in the digestive tract, probiotic supplementation should accompany antibiotic treatment. Mega doses of some vitamins, minerals, and other supplements are also known to cause diarrhea.

Stress and Excitement: It's well known that stress, anxiety, and excitement can cause diarrhea in some people and dogs are no different. Some dogs respond to heightened stress or excitement (e.g., travel, new places and situations, thunderstorms) with digestive upsets resulting in diarrhea or vomiting.

Dog Diarrhea Causes - Chronic

Parasites: Intestinal worms such as hookworms and whipworms as well as protozoa such as Giardia and Coccidia can cause chronic canine diarrhea. In cases of ongoing diarrhea, it's a good idea to rule out parasites as the cause before examining more serious possibilities. Since some of these parasites can be difficult to detect in a fecal examination, a broad-spectrum parasiticide is often administered even in cases of negative fecal tests.

Food Allergies: Allergies to specific foods can cause many symptoms, diarrhea being one of them. To determine whether a food allergy is the cause of a dog's chronic diarrhea, the dog is temporarily switched to a special limited ingredient diet consisting of a single protein source and a single carbohydrate source the dog has never eaten before.

No other foods, treats, or supplements should be fed during this time.

If the diet change eliminates the diarrhea, ingredients can slowly be added back, one by one, until the allergen(s) is/are identified. Alternatively, a special dog food utilizing a hydrolyzed protein source may be an option.

Pancreatitis: Pancreatitis refers to the inflammation of the pancreas and can be acute or chronic. In cases of chronic pancreatitis, the inflammation is constant and ongoing, and may occasionally flare up into acute pancreatitis. Sporadic vomiting, pain and discomfort (especially after eating), difficulty digesting fats, reduced appetite, and weight loss are symptoms that may accompany chronic pancreatitis.

Liver Disease: Chronic diarrhea can be an early symptom of liver disease in dogs. The type of diarrhea usually associated with liver disease originates in the small intestine and often includes undigested fats.

Cancer: Dogs, especially older dogs, can develop gastrointestinal cancers, of which lymphosarcoma is the most common. These cancers can cause chronic diarrhea, vomiting, and a host of other symptoms. The possibility of cancer is a reason why starting dogs on prednisone without running diagnostic tests to determine the cause of the dog's diarrhea is a bad idea.

Not only will prednisone treatment make detection of the cancer more difficult, but even a short course of corticosteroids greatly diminishes the prognosis should the diarrhea cause turn out to be lymphosarcoma.

Irritable Bowel Syndrome (IBS): Not to be confused with Inflammatory Bowel Disease (IBD), Irritable Bowel Syndrome (IBS) is a functional gastrointestinal disorder with a psychological component. Stress and anxiety can exacerbate symptoms, but IBS is no longer considered primarily a psychosomatic disorder. Diarrhea caused by IBS usually originates in the large intestine and is frequently accompanied by gas, bloating, cramps, and abdominal pain.

Hypoadrenocorticism (Addison’s disease): Hypoadrenocorticism or Addison’s disease results from the insufficient production of corticosteroids by the adrenal gland. Addison’s disease can have a number of causes, but the most common is destruction of the adrenal gland by the immune system. In addition to diarrhea, dogs with hypoadrenocorticism may experience lack of appetite, vomiting, lethargy, and weakness.

Hypothyroidism: Hypothyroidism occurs when the thyroid gland fails to produce sufficient thyroid hormones. In the vast majority of cases (over 95%), canine hypothyroidism is an autoimmune disease in which the dog's own immune system destroys the thyroid gland.

The failure to generate adequate amounts of thyroid hormone results in a host of possible symptoms including gastrointestinal disturbances.

Other typical symptoms include weight gain (often despite calorie restriction), various skin and coat problems including hair loss, lethargy, weakness, and behavioral changes.

Exocrine Pancreatic Insufficiency (EPI): EPI is a disorder in which the pancreas fails to produce enough of the enzymes needed to digest food. Dogs with EPI waste away despite a voracious appetite. Chronic diarrhea is a typical symptom of EPI and bowel movements are frequent, large in volume, often yellow in color, and very greasy due to the presence of undigested fats.

Colitis: Colitis is a general term referring to inflammation of the large intestine (see "Symptoms of Dog Diarrhea Caused by Large Intestine" above). Colitis may be acute or chronic. The potential causes of colitis can be as innocuous as a temporary irritation from eating grass or as serious as IBD, IBS, and cancer. Parasites and bacterial overgrowth can also cause chronic colitis.

Inflammatory Bowel Disease (IBD): IBD is a very common cause of chronic diarrhea in dogs. The disease is characterized by inflammatory immune cells that infiltrate the lining of the gastrointestinal tract, causing chronic inflammation that leads to a thickening of the intestinal wall as normal tissue is replaced by fibrous, scar-like tissue. This thickening interferes with the bowel's ability to contract, move food around, and absorb nutrients.

The symptoms of IBD can vary depending on where in the GI tract the inflammation is located. When the inflammatory cell infiltration occurs in the stomach or the upper region of the small intestine, chronic vomiting is typically the result.

Infiltrations in the lower part of the small intestine typically result in watery diarrhea, increased stool volume, and weight loss, while involvement of the large intestine is characterized by mucous-heavy diarrhea, straining to have bowel movements, and often increased urgency and frequency. Fresh blood in stools is also quite common.

Some cases of IBD involve the inflammation of the entire GI tract, from top to bottom.

There are several types of IBD, with the lymphocytic-plasmacytic variety (so named because the invading inflammatory cells are lymphocytes and plasmacytes) being the most common. Eosinophilic IBD (in this case, the cells infiltrating the lining of the intestines or stomach are eosinophils) is the second most common form. IBD can be treated and controlled, but it is rarely cured.

Read more about IBD Symptoms and IBD Treatment.

This list of acute and chronic dog diarrhea causes is not complete, but it does cover the most common culprits. Other possible chronic dog diarrhea causes include small intestine bacterial overgrowth (SIBO), protein-losing enteropathy (PLE), leaky gut syndrome (LGS), and kidney disease.