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Diarrhoea in Dogs: Causes and Treatment
 
Diarrhoea 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 diarrhoea in dogs are dietary indiscretion and intestinal parasites. Many canine infectious diseases are also associated with acute diarrhoea.

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 diarrhoea 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 intolerance can 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 diarrhoea.

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

Diarrhoea 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 diarrhoea.

Dogs may also experience diarrhoea 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 diarrhoea.
 
Home treatment of diarrhoea 
The most important step in treating acute diarrhoea 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 diarrhoea, 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 diarrhoea 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 chicken with the skin removed. Cooked white rice, cottage cheese, cooked plain pasta and soft-boiled eggs are other easily digestible foods. Feed three or four very 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 diarrhoea is consistent and continues for more than 48 hours
• The stool contains blood or is black and tarry
• The diarrhoea is accompanied by vomiting
• The dog appears weak or depressed or has a fever

Chronic diarrhoea
The first step is to find and treat the underlying cause. Diarrhoea 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 is suspected, eliminate milk and dairy products from the diet, particularly as they are not required for adult dogs.
 
Diarrhoea 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 diarrhoea that persists for more than three weeks requires veterinary attention.

With thanks to webMD