Diarrhea in Dogs: Causes and Treatment

Diarrhea is the passage of loose, unformed stools. In most cases there is a large volume of stool and an increased number of bowel movements. The two most common causes of diarrhea in dogs are dietary indiscretion and intestinal parasites. Many canine infectious diseases are also associated with acute diarrhea.

Food takes about eight hours to pass through the small intestines. During that time, the bulk of the food and 80 percent of the water is absorbed. The colon concentrates the remainder. At the end, a well-formed stool is evacuated. A normal stool contains no mucus, blood, or undigested food.

With rapid transit through the bowel, food arrives at the rectum in a liquid state, resulting in a loose, unformed bowel movement. This type of rapid transit accounts for the majority of temporary diarrhea in dogs.

Dietary indiscretion is a common cause of rapid transit. Dogs are natural scavengers and tend to eat many indigestible substances, including garbage and decayed food, dead animals, grass, wild and ornamental plants, and pieces of plastic, wood, paper, and other foreign materials. Many of these are irritating to the stomach as well as to the bowel, and are partially eliminated through vomiting.

Food intolerancecan also cause rapid transit. Foods that some dogs seem unable to tolerate can include beef, pork, chicken, horsemeat, fish, eggs, spices, corn, wheat, soy, gravies, salts, spices, fats, and some commercial dog foods. Note that food intolerance is not the same as food allergy, which causes dermatitis and possibly vomiting, but rarely causes diarrhea.

Characteristics of Diarrhea


Likely Cause

Likely Location

Yellowish or greenish

Rapid transit

Small bowel

Black, tarry

Upper GI bleeding

Stomach or small bowel

Red blood or clots

Lower GI bleeding

Colon clots

Pasty, light

Lack of bile


Large, gray, rancid

Inadequate digestion

Small bowel or absorption


Likely Cause

Likely Location


Rapid transit

Small bowel


Bacterial infection

Small bowel

Greasy, often with oily hair around the anus


Small bowel, pancreas

Glistening or jellylike

Constains mucus



Likely Cause

Likely Location

Foodlike, or smelling like sour milk

Rapid transit and inadequate digestion or absorption (suggests overfeeding, especially in puppies)

Small bowel

Rancid or foul

Inadequate digestion with fermentation

Small bowel, pancreas


Likely Cause

Likely Location

Several small stools in an hour, with straining



Three or four large stools in a day

Inadequate digestion or absorption

Small bowel, pancreas

Condition of the Dog

Likely Cause

Likely Location

Weight loss

Inadequate digestion or absorption

Small bowel, pancreas

No weight loss, normal appetite

Large bowel disorder




Small bowel, rarely colon

Intestinal parasites are a common cause of acute and chronic diarrhea in puppies and adults. The greatest problems are caused by roundworms, hookworms, whipworms, threadworms, and giardia.

Diarrhea is a common side effect of many drugs and medications, particularly the NSAIDs,which include aspirin. Some heart medications, some dewormers, and most antibiotics also can cause diarrhea.

Dogs can experience diarrhea when they're excited or upset-for example, when they're going to the veterinary hospital or a dog show. In fact, any sudden change in a dog's diet or living circumstances may cause emotional diarrhea

Home Treatment of Diarrhea

The most important step in treating acute diarrhea is to rest the GI tract by withholding all food for 24 hours. The dog should be encouraged to drink as much water as he wants. With persistent diarrhea, consider giving a supplemental electrolyte solution such as Pedialyte, available over the counter in pharmacies and grocery stores. Dilute it by one-half with water and add it to the dog's drinking bowl. Custom canine electrolyte solutions and sport drinks are also available, such as K9 Thirst Quencher. These are flavored to encourage the dog to drink. If the dog won't drink the electrolyte solution, offer only water. A low-salt bouillon cube dissolved in the water can help encourage him to drink.

Acute diarrhea usually responds within 24 hours to intestinal rest. Start the dog out on an easily digestible diet that's low in fat. Examples are boiled hamburger (one part drained meat to two parts cooked rice) and boiled chicken with the skin removed. Cooked white rice, cottage cheese, cooked macaroni, cooked oatmeal, and soft-boiled eggs are other easily digestible foods. Feed three or four small meals a day for the first two days. Then slowly switch the diet back to the dog's regular food.

Obtain immediate veterinary care if:

  • The diarrhea continues for more than 24 hours
  • The stool contains blood or is black and tarry
  • The diarrhea is accompanied by vomiting
  • The dog appears weak or depressed or has a fever

Chronic Diarrhea

The first step is to find and treat the underlying cause. Diarrhea resulting from a change in diet can be corrected by switching back to the old diet and then making step-by-step changes to pinpoint the cause. When lactase deficiency issuspected, eliminate milk and dairy products from the diet, particularly as they are not required for adult dogs.

Diarrhea caused by overeating (characterized by large, bulky, unformed stools) can be controlled by tailoring the diet more accurately to the caloric needs of the dog and feeding his daily ration in three equal meals.

Chronic, intermittent diarrhea that persists for more than three weeks requires veterinary attention.

This article is excerpted from “Dog Owner’s Home Veterinary Handbook” with permission from Wiley Publishing, Inc.

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