I. Anatomy of the Stomach and Intestines in Dogs

The anatomy of the digestive tract in dogs is very similar to that of people. Chewed food passes from the mouth, down the esophagus and into the stomach. From the stomach, food passes into the small intestines (the duodenum is the first part of the small intestine), then the large intestine or colon, and then to the rectum, where stool is stored until a dog is ready to use the bathroom (defecate).

Digestion begins in the stomach and continues in the small intestines. The stomach and small intestines make enzymes that breaks food up into particles small enough for the body to absorb. The small intestines also add water to the food to help with digestion. Most of this water is re-absorbed later in the small intestines along with nutrients from food. The large intestine absorbs even more water, making stool firm when it is excreted. Inside the intestines, there is also a normal population of bacteria. These bacteria help with digestion and protect the intestines from infections with organisms that might cause disease.

II. Diarrhea

Diarrhea, very simply, can be defined as too much water in the feces. Too much water can end up in the feces several ways. These include:

• If too many food particles are present in the intesines, this prevents them from absorbing enough water. This occurs with over-eating, when rapid changes in the diet are made, and during stressfull situations. When a dog eats too much, there may not be enough digestive enzymes produced to breakdown all of the food. When a rapid change in diet is made, digestive enzymes do not have time to adjust to the new type of food. During stressful situations, the amount and type of digestive enzymes change. In all of these situations, more undigested food is left in the intestines. These extra food particles hold on to water and keep it from being absorbed by the intestines.


• The addition of too much water into the food by the small intestines. This occurs with intestinal infections and when dogs eat spoiled food out of the trash. It can also happen with intestinal parasites. Salmonella and E. Coli cause problems like this.

Most cases of abrupt onset diarrhea in dogs are caused by rapid changes in diet, eating out of the trash can, stress and intestinal parasites. Some dogs also get diarrhea when they take antibiotics. In many of these cases, dogs do not get severely ill. If a dog does get severely ill with diarrhea and develop other symptoms, this is an indication that there may be a systemic illness causing diarrhea. For these dogs, it is important that they see a veterinarian immediately.

III. The Veterinary Visit – Why does my Dog have Diarrhea?

Many dogs with simple diarrhea may not need a trip to the veterinarian. If a dog has mild diarrhea that is not making it uncomfortable, has no other symptoms, and does not otherwise feel bad, it is OK to wait 24-36 hours to see a veterinarian. Many cases of simple diarrhea will resolve on their own. If a dog has diarrhea and seems uncomfortable, if the diarrhea appears bloody or like tar, if the dog has other symptoms, or seems sick, then it is wise to see the veterinarian right away. Even if the diarrhea does not go away any faster after the veterinary visit, the veterinarian can evaluate the dog and make sure nothing more serious is going on and can give medication to make the dog more comfortable.

After the veterinarian examines the patient, he or she will want a fresh stool sample. If your dog has recently (in the last 30-45 minutes) had a bowel movement, you can collect that and take it with you. If not, the veterinarian can collect a sample in the office. Several things will be done with the stool sample. These include:

• A fecal flotation to check for intestinal parasites


• A direct fecal smear to check for red blood cells, white blood cells and abnormal or unusual bacteria.

A fecal smear with abnormal bacteria (the ones that look like tennis racquets)

If a dog has had diarrhea for several days, has bloody diarrhea, seems to be very ill, or has other symptoms such as vomiting, it’s a good idea to have blood work and x-rays done. Both of these tests are used to check for other systemic illnesses that might be causing diarrhea.

IV. Treatment of Diarrhea

For the dog with simple diarrhea that is still eating and drinking and feeling fine, home management may be the only treatment needed. For 24-48 hours, feed boiled, skinless, boneless, chicken breast with cooked white rice. If possible, feed small meals every 2-4 hours. Bland food fed in frequent, small amounts gives the intestines time to calm down and readjust. Once diarrhea has resolved, gradually begin re-introducing the normal food. If the diarrhea does not resolve or comes back after reintroducing normal food, it is time to see the veterinarian for more treatment options.

Simple diarrhea in dogs is usually treated in several ways.

• Antibiotics such as metronidazole are frequently used to treat cases of colitis and enteritis. They help to remove abnormal bacteria.


• Medications such as Kaolin and Pectin can be used with metronidazole. They help firm the stool and stop diarrhea more quickly than it would stop on its own.


• Probiotics are sometimes used also. These are beneficial bacteria that help restore the balance of normal bacteria in the intestines. Some probiotics are used to treat diarrhea and others can be used to prevent diarrhea.


• Food that is bland, such as boiled chicken and white rice, gives the intestines a chance to calm down and readjust.

Do not give your dog over the counter medications such as Immodium, Kaopectate, or Pepto-Bismol without checking with your veterinarian first. Most cases of simple diarrhea respond to treatment within a few days. If your dog continues to have diarrhea, you may need to re-visit the veterinarian for more testing or a change in therapy. The video below discusses treatment of simple diarrhea.

If your dog has bloody or tarry diarrhea, has other symptoms with the diarrhea, or does not seem to feel well, it is important that you make an appointment to see the veterianarian right away. Dogs with very severe diarrhea or other systemic illness causing diarrhea can get worse rapidly.

V. Prevention

Here are some easy things you can do to prevent many cases of diarrhea:

• Keep trash, human food, and medications locked up and out of reach of your dog.


• Do not feed your dog human food or table scraps.


• Supervise your dog when outside to make sure it does not eat something it should not.


• If you need to change your dog’s diet, do so gradually by mixing the new food and the old food. Slowly increase the amount of new food and decrease the amount of old food until you are feeding only the new food. Make this change over at least seven days. Some dogs may need longer.


• If you take your dog to board or stay with someone else, take your own dog food.


• Deworm your dog every month. Most heartworm preventives will also deworm a dog.

No information in this article is designed to diagnose or treat your pet nor should it replace a visit to your veterinarian for appropriate diagnosis and treatment.