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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

Color

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

Liver

Large, gray, rancid

Inadequate digestion

Small bowel or absorption

 

Consistency

Likely Cause

Likely Location

Watery

Rapid transit

Small bowel

Foamy

Bacterial infection

Small bowel

Greasy, often with oily hair around the anus

Malabsorption

Small bowel, pancreas

Glistening or jellylike

Constains mucus

Colon

 

Odor

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

 

Frequency

Likely Cause

Likely Location

Several small stools in an hour, with straining

Colitis

Colon

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

Colon

Vomiting

Enteritis

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

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