Diarrhea in Dogs: Causes & Treatment

Updated on September 9, 2017
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eirevet is a veterinarian specialized in canine and feline internal medicine and owns a small animal veterinary hospital in Ireland.

What Causes Diarrhea?

In dogs, like in other animals, diarrhea is not a disease in itself but rather a symptom of problems within the gastrointestinal tract (GIT). It may or may not be accompanied by vomiting. Diarrhea without vomiting is termed enteritis, whereas dogs with both vomiting and diarrhea are said to suffer from gastroenteritis. As with vomiting, dogs use diarrhea to flush toxins or infectious agents from the GIT in order to prevent more serious illness. The most common causes of diarrhea in dogs presenting to my clinic are dietary indiscretion (overeating or eating spoiled food) and stress (often seen after a period in kennelling).

Dog diarrhea can be caused by any problem which upsets the fine balance between fluid absorption and secretion in the GIT. Diseases of the bowel, liver, pancreas, adrenal glands, kidneys, and many other organs can cause diarrhea.

Veterinarians will describe a dog's diarrhea as being small or large-bowel in character. Small bowel diarrhea is usually more liquid, may range in color from yellow to black, and is passed infrequently (usually 2-3 times per day). Large bowel diarrhea is more often a normal colour, may contain streaks of blood and mucus, and is passed much more frequently than usual. Straining to defecate is another common feature of large bowel diarrhea.

Structure of the small intestine

Diagram of a tiny section of small intestine. Notice the many tiny projections on the surface of the absorptive cell- damage to these is a common reason for diarrhea in dogs
Diagram of a tiny section of small intestine. Notice the many tiny projections on the surface of the absorptive cell- damage to these is a common reason for diarrhea in dogs

What Causes Diarrhea in Dogs?

The process of turning ingested food into formed fecal matter involves an extraordinary, complex series of processes involving many different organs in the body. Diarrhea in dogs can result from a problem in any one (or several) of these processes. Bodily fluids are added to chewed food (ingesta) in the mouth (from the salivary glands), from the stomach, liver, pancreas and small intestines. Enzymes, acids, electrolytes and other substances are also added to ingesta along the way, most of which must be reabsorbed into the bloodstream to maintain your dog's health.

During digestion, the breakdown of food produces millions of tiny particles within the gut. If these particles are not absorbed very efficiently by the small intestine they will draw water into the gut, causing osmotic diarrhea in dogs. Lactose intolerance in dogs would be one common cause of secretory diarrhea due to unabsorbed sugar molecules in the gut.

Infection with E. coli or other bacteria or viruses may cause damage to the millions of delicate fronds (microvilli) of the small intestine which are mainly responsible for fluid reabsorption. This exudative or secretory dog diarrhea results in the loss of large volumes of water and electrolytes and may result in severe illness.

Does your dog have small or large bowel diarrhea?

Small Bowel Diarrhea
Large Bowel Diarrhea
Frequency of defecation
Normal to slightly increased
Greatly increased
Volume of feces
Straining to defecate
Excessive mucus in feces
Not usually
Blood in feces
Black feces (bleeding from stomach or small intestine)
Fresh red blood
Weight loss or other systemic signs
Not usually
General features which may be used to try to localise the source of the diarrhea.

Management of Diarrhea

If your dog is bright, alert, eating and drinking in spite of his diarrhea, it is often possible to use home remedies to settle his stomach and avoid a costly trip to the veterinary clinic. This is more often the case with large bowel diarrhea, where the cause is usually one of the aforementioned dietary indiscretion or stress. Small bowel diarrhea contains greater amounts of electrolytes and water, and your dog is more likely to dehydrate and become more unwell. Any sign of black feces or feces containing fresh blood should prompt an immediate visit to your veterinary surgeon.

If your dog is refusing food and/or water, is very depressed, or is also vomiting, you would also be well advised to consult your vet. Dogs with diarrhea that are very unwell are more likely to have underlying problems such as kidney disease. The simple management tips listed below should only be used for a period of 24 hours. If the problem persists after this period it is unlikely to clear up without further investigation.

Parvovirus virions- one of the more serious potential causes of dog diarrhea
Parvovirus virions- one of the more serious potential causes of dog diarrhea

Puppies with Diarrhea—A Special Case

Any puppy under 16 weeks of age with diarrhea should not be managed at home except under veterinary direction. Young pups are far more likely to have a serious infectious disease such as parvovirus, and will also succumb to dehydration and electrolyte imbalance much more quickly than an adult dog.

Diarrhea remedy

Vet Solutions Pro-pectalin Anti-diarrheal Tablets for Dogs and Cats, 250 Tablets
Vet Solutions Pro-pectalin Anti-diarrheal Tablets for Dogs and Cats, 250 Tablets

We use this product in our hospital to treat mild, self-limiting diarrhea and it can be a very useful product to have at home for anyone with several dogs or a dog prone to bouts of enteritis.


Home Remedies

"Well" dogs, as discussed above, may be managed at home by a conscientious owner. The first step in treating these animals is to withhold all solid foods for a period of 24 hours. This will allow the intestines to empty and to re-establish their normal rhythm and function. During this fast, offer water or water with electrolytes to maintain your dog's hydration levels. Rice water is another very commonly used substance during a period of fasting. As the name suggests, this is simply the water used when boiling white rice, cooled and offered as a drink. This contains both electrolytes and starch, which is used as a source of energy.

Preparations containing kaolin and pectin help to firm up the feces, while probiotics may be useful to combat any overgrowth of pathogenic (bad) bacteria in the gut. The vet solutions product below contains these active ingredients.

Following this 24-hour fast of small frequent meals of boiled white rice and boiled or steamed chicken or white fish should be offered for a period of 2-3 days before slowly reintroducing his normal diet. This is assuming your dog is not having any further bouts of diarrhea.

Caring for Your Dog's Digestive Health

Feeding a good quality diet without frequently changing brands or types of dog food will help prevent digestive upsets. Regular deworming is essential to reduce the number of parasites your dog may be carrying, both for his and your own health.

If your dog is suffering from severe or recurring bouts of diarrhea, it is important your veterinary surgeon investigates the possibility of underlying disease. Young dogs are more likely to have infectious gastrointestinal problems, while inflammatory bowel disease and bowel tumours (cancer) are more likely in older dogs.

Canine Parasite

Canine roundworm specimen
Canine roundworm specimen

Deworming survey

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Lactobacillus probiotic

Probiotic Miracle Dog Probiotics for Dogs (Up to 360 Servings)
Probiotic Miracle Dog Probiotics for Dogs (Up to 360 Servings)

Contains several species of beneficial Lactobacillus bacteria to promote intestinal and immune health. Provided as a powder for mixing with your pet's normal diet.


Probiotics for Dogs

As is the case in human medicine, there is a steadily growing bank of evidence to show that probiotic supplements may be beneficial to general health as well as the health of the GIT. Probiotics contain 'friendly' bacteria such as Enterococcus faecium which can help prevent the overgrowth of pathogenic bacteria in the gut. There is also some evidence to show that these good bacteria play a role in stimulating a healthy immune system, and may even help dampen allergic responses, such as those seen in inflammatory bowel disease or canine atopic skin disease. A recent study also showed a probiotic containing Lactobacillus cultures to help combat intestinal hookworm infestation. Although much research remains to be done on the exact indications for probiotic treatment, it seems clear that this harmless supplementation of the diet is likely to be beneficial to your dog's health.


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