St. Charles Animal Hospital

11685 Doolittle Drive
Waldorf, MD 20602


Diarrhea and Vomiting


Diarrhea is defined as loose or unformed stools. The intestinal tract has the capability of reabsorbing 99.99% of the fluid that is presented to it, if it is working correctly. We all know that if we drink a half-gallon of water, it does not cause diarrhea, it simply makes us urinate more. That is because the colon reabsorbs all of that excess water and our kidneys get rid of that excess.

Vomiting is defined as the forceful expulsion of stomach contents.

Causes of Diarrhea

Probably 90% of the sudden onset diarrhea cases are caused by eating something that has upset the gastrointestinal system. It could be as simple as eating a food or treat that your dog is not accustomed to and this triggered an intolerance or irritation to the GI tract. This irritation causes an increase in the speed of movement through the system and possibly an increase in secretions by the system. That combination leads to a decreased absorption of fluid and therefore loose stool. If the irritation is severe enough, it will also trigger inflammation throughout the system, leading to mucus production in the colon or even the appearance of fresh blood and straining. These are the hallmarks of colitis, which simply means inflammation of the colon. Once the offending substance has been eliminated from the system, usually the GI system recovers completely on its own.

However, sometimes, after a sudden bout of diarrhea, we are presented with a diarrhea that does not want to go away. Why? Consider that the dog's colon is loaded with bacteria. We estimate that 95% of those bacteria are good for the system and about 5% are bad. This ratio is maintained by the GI tract when things are healthy. With a sudden severe diarrhea, sometimes the bulk of the bacteria are flushed out of the colon, leaving behind a liquid environment that is more conducive for the "bad bacteria" to flourish. Once those bacteria overgrow, they tend to maintain the conditions that favor their continued growth. In those cases of "bacterial overgrowth", veterinary intervention is often required to break that cycle.

Continuous inflammation of the gastrointestinal tract is called Inflammatory Bowel Disease. This inflammation may be from continuous irritation from certain foods, or even from a food allergy. Sometimes it is the dog's immune system that is over-reacting to normal bacteria or normal food elements! This inflammation may affect all areas of the GI system or be more prominent in one area of the GI system, leading to specific signs of either loose stools, weight loss from lack of proper absorption of nutrients, mucus production, bleeding, straining to defecate or a combination of symptoms.

Occasionally dogs actually pick up a specific bacteria that will cause uncontrollable diarrhea. Examples include Campylobacter, Salmonella, and E. Coli.

Sudden onset diarrhea and vomiting may also be from a virus. The most notorious virus is Parvovirus. This virus is very contagious, especially to young dogs. Fortunately, the "Distemper" vaccine that your dog gets on a routine basis, includes Parvo as one of its components. So, most of our cases of Parvovirus occur in unvaccinated dogs.

Parasites of the intestinal tract do cause diarrhea, but most commonly, the diarrheas are not sudden onset. They seem to develop slowly and progress and worsen if treatment is not pursued. These include Roundworms, Hookworms, Whipworms, Coccidia, and Giardia. Tapeworms can be found in the stool of dogs and cats, but actually, rarely causes diarrhea.


It is, of course, necessary to figure out whether the vomiting and diarrhea problems are caused by something simple and self-limiting, or something more serious. This is not always easy to do. A really good history is extremely helpful. There are many times where dietary indiscretion is fairly obvious. Those cases are pretty straight forward. In most other cases a good physical examination is needed to rule in or out some serious things. If the history and physical exam do not give us a treatment plan, then another appropriate step is to do some testing on the stool, looking for parasites and abnormal bacteria.

In some cases, the next step will be abdominal radiographs (X-rays), which can usually be done while you wait. Radiographs may show signs of a foreign body lodged in the stomach or intestinal tract, or signs of a partial or complete obstruction. If the "plain radiographs" are not diagnostic, the next step could be either a barium series or an abdominal ultrasound.

Blood work is commonly done if your pet is ill. It is not common to find the reason for "sudden onset" diarrhea or vomiting on blood work, but those laboratory tests will tell us if your pet is dehydrated or if any of the important organs are affected. They are also vital to us if your pet should require anesthesia or surgery.


If your dog has a simple case of diarrhea, where there is NO vomiting, NO loss of appetite, NO pain, NO loss of energy, and NO blood in the stool, then it is usually safe to treat at home for one day. Depending on whom you talk to, you may get several different suggestions for "home remedies". My personal belief is that Mother Nature is pretty good at fixing simple things if we do not interfere. In these simple cases, I usually suggest taking away ALL food for a period of 24 hours to give the GI tract a chance to rest and recover. (Note: the withholding of food is NOT appropriate for puppies and kittens or for obese cats. In those cases, you should seek veterinary help!) You may continue to offer water, unless there is vomiting! (If vomiting and diarrhea are occurring at the same time, then veterinary care is needed!!) After the 24 hour period of no food, you should give a meal to your dog consisting of ? of the NORMAL food that your dog has been getting. Do NOT change foods! Most people that have had dogs for a long time know that a sudden change of diet frequently CAUSES diarrhea. If the diarrhea is not improving, then a visit to the vet is appropriate.

Treatment by a veterinarian will depend on the history, physical exam, diagnostic tests, and the eventual diagnosis. They may include antibiotics +/- a Probiotic for a bacterial overgrowth, anti-inflammatory drugs or diet changes for Inflammatory Bowel Disease, or scoping for a GI foreign body, or surgery for an obstruction. If your dog has both vomiting and diarrhea, you can expect fluid therapy to help treat dehydration.

Causes of Vomiting

As with diarrhea, many cases of sudden onset vomiting are from dietary indiscretion. Dogs will eat anything! Sometimes the stinkier it is, the faster it will go down their throat! It has always been amazing to me that dogs will often reject various flavors of dog food, but will eat spoiled garbage! Cats are a little more fussy at what they swallow, but still get themselves in trouble from time to time. Dogs and cats vomit much easier than humans. So, the slightest thing that irritates their stomach will often result in vomiting.

If the vomiting was from a food item, hopefully, vomiting once or twice should clear the system of that food. If that is the case, with rest, the vomiting should resolve. If, on the other hand the pet has swallowed a foreign body, (bone, string, metal, rubber, glass, etc.) that substance may stay in the stomach and continue to irritate the stomach lining, leading to continual vomiting. If this foreign body moves down to the small intestines, it may lodge leading to an obstruction.


A good history may reveal the cause of the vomiting. If not, abdominal radiographs may help. If a diagnosis cannot be reached, then blood work may reveal that the vomiting is from disease in one of the major organs (liver or kidney). If we have a history of possibly consuming a foreign object and if the radiographs are compatible with that diagnosis, scoping may be the next step for both diagnosis and treatment. We use color video equipment that is similar to what your GI Internist would use on you to do Colonoscopy, but our scopes are a thinner diameter. With the scope, we are able to remove most stomach foreign bodies without surgery.


Once again, treatment will depend on the history and diagnosis. If you suspect that your pet has eaten something that has irritated his stomach, it is usually safe to wait a few hours to see if rest will help. This is provided that there is NO diarrhea, your pet is NOT in pain, and has good energy levels. If your pet has both vomiting and diarrhea, then veterinary care is essential, since this will quickly lead to dehydration.

Foreign body ingestion is most easily treated with immediate scoping (Gastroscopy). The scope, unfortunately will only go a short distance down the small intestines, so if a foreign body gets lodged in the intestines, surgery is usually needed.