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Dog Diarrhea: Causes and Treatment

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Eirevet is a veterinarian specialized in canine and feline internal medicine who owns a small animal veterinary hospital in Ireland.

What causes gastrointestinal upset in dogs?

What causes gastrointestinal upset in dogs?

Why Do Dogs Get 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 illnesses. Some of the most common causes of diarrhea in dogs are dietary indiscretion (overeating or eating spoiled food) and stress (often seen after a period of kennelling). In addition, 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.

Small vs. Large-Bowel Diarrhea

Veterinarians will describe 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 color, 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.

A diagram of a tiny section of the 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.

A diagram of a tiny section of the 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.

With digestion, 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.

Small vs. Large-Bowel Diarrhea

General features which may be used to try to localise the source of the diarrhea.

SymptomSmall Bowel DiarrheaLarge 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

How to Manage Diarrhea in Dogs

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, like dietary indiscretion or stress. Small-bowel diarrhea contains greater amounts of electrolytes and water, during which 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.

When to See a Veterinarian

If your dog is refusing food and/or water, is very depressed, or is also vomiting, you are 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.

Puppies Require Veterinary Care

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.

Parvovirus virions—one of the more serious potential causes of dog diarrhea.

Parvovirus virions—one of the more serious potential causes of dog diarrhea.

Home Remedies: The Bland Diet and 24-Hour Fast

"Well" dogs, as discussed above, may be managed at home by a conscientious owner.

The 24-Hour Fast

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

Rice water is another 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.

Kaolin-Pectin and Probiotics

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.

When to Reintroduce Food

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 a 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. Also, 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 that your veterinary surgeon investigates the possibility of an underlying disease. Young dogs are more likely to have infectious gastrointestinal problems, while inflammatory bowel disease and bowel tumors (cancer) are more likely in older dogs.

Canine roundworm specimen. Gross!

Canine roundworm specimen. Gross!

Do Probiotics Help 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. 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.

Learn More About Digestion

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.