This information is not meant to be a substitute for veterinary care.
Always follow the instructions provided by your veterinarian.
Diarrhea is the passing of loose or liquid stool, more often
than normal. Diarrhea can be caused by diseases of the small intestine,
large intestine or by diseases of organs other than the intestinal tract.
Your ability to answer questions about your pet's diet, habits, environment
and specific details about the diarrhea can help the veterinarian narrow the
list of possible causes, and to plan for specific tests to determine the
cause of diarrhea. (Anatomy of the digestive system:
Small intestinal and large intestinal diarrhea have different causes,
require different tests to diagnose and are treated differently. Small
intestinal diseases result in a larger amount of stool passed with a mild
increase in frequency; about 3 to 5 bowel movements per day. The pet doesn't
strain or have difficulty passing stool. Animals with small intestinal
disease may also vomit and lose weight. Excess gas production is sometimes
seen and you may hear the rumbling of gas in the belly. If there is blood in
the stool it is digested and black in color.
Disease of the large intestine including the colon and rectum cause the
pet to pass small amounts of loose stool very often, usually more than 5
times daily. The pet strains to pass stool. If there is blood in the stool,
it is red in color. The stool may be slimy with mucus. The pet does not
usually vomit or lose weight with large bowel diarrhea. A sudden onset of
small intestinal diarrhea may be caused by viruses including canine
distemper, canine parvovirus, canine coronavirus, feline panleukopenia virus
or feline coronavirus, in young, poorly vaccinated pets. Small intestinal
diarrhea can be caused by bacteria such as salmonella, clostridia or
campylobacter although these same bacteria can be found in the stool of
normal dogs and cats.
Worms and giardia can cause small intestinal
diarrhea, mostly in young animals. Foreign bodies including bones, sticks
and other objects can pass through the stomach and get stuck in the
intestine causing both diarrhea and vomiting. These same foreign materials
may pass through the intestinal tract without getting stuck but may damage
the lining of the intestinal tract causing diarrhea. Dietary indiscretion or
a sudden change in diet can cause diarrhea with or without vomiting. Food
allergies in dogs and cats can cause diarrhea, vomiting or itchy skin.
Toxins including lead and insecticides can cause diarrhea usually with
vomiting. Inflammatory bowel disease (IBD) occurs commonly in both dogs and
cats. In IBD the walls of the intestine contain abnormal numbers of
inflammatory cells which can be eosinophils, lymphocytes or plasma cells.
The cause of IBD is not known but is suspected to be an allergic reaction to
components of food, bacteria or parasites. IBD can be congenital in some
breeds of dogs, for example Basenji dogs may develop a severe inflammatory
bowel disease. Tumors of the intestine are another cause of diarrhea usually
occurring in older pets. The tumor may be a single mass when the tumor is
from the glands of the intestine (adenocarcinoma) and may be removed by
surgery or the tumor may occur diffusely along the intestine. Lymphosarcoma
occurs in both dogs and cats and can either be a single or multiple masses
in the intestine or the abnormal lymphocytes may be spread through out the
intestine. Lymphosarcoma is often responsive to anti-cancer drugs in cats
but rarely responds to anti-cancer drugs in dogs.
In certain parts of the country small intestinal disease can be caused by
fungal infections including histoplasmosis. Your veterinarian can discuss
with you whether histoplasmosis is seen in your part of the country.
Diseases outside the intestinal tract that may cause diarrhea include kidney
failure, liver failure, pancreatic disease and hyperthyroidism in the cat.
Severe inflammation of the pancreas (pancreatitis) can lead to damage of the
pancreas and an inability to make enough enzymes to digest fat. This is
called pancreatic insufficiency and causes diarrhea with a large volume of
greasy stool. Pancreatic insufficiency can occur in young animals due to a
congenital deficiency of pancreatic enzymes.
The cause of small intestinal diarrhea may be determined from blood
tests, examination of the stool, x-rays or ultrasound of the abdomen or by
endoscopy. Endoscopy is the technique of passing a flexible scope through
the stomach into the upper intestine. Small biopsies of the lining of the
intestine can be taken for microscopic evaluation. Endoscopy requires
general anesthesia. A diagnosis of intestinal lymphosarcoma may be missed on
endoscopy as the biopsies taken using endoscopy do not include the full
thickness of the wall of the intestine and the cancerous cells may be deep
in the wall of the intestine. A diagnosis in that case requires surgery in
order to take a larger biopsy of the entire thickness of the intestine.
Dogs and cats with chronic small intestinal diarrhea will lose weight as
they are unable to properly absorb nutrients and may develop edema of the
legs or fluid accumulation in the belly or chest. A small protein, albumin
may be lost in diarrhea. Albumin acts like a sponge to keep water in the
blood vessels. When albumin is lost in the stool, blood albumin gets low and
water leaks out of blood vessels to accumulate in other locations. Chronic
diarrhea may cause the fur to look dull and brittle due to nutrient
deficiencies. Acute small intestinal diarrhea can be managed by withholding
food, but not water for 24 - 48 hours. If diarrhea stops, small amounts of a
bland low-fat food are fed 3 to 6 times daily for a few days, with a gradual
increase in the amount fed and a gradual transition to the pet's normal
diet. Foods designed as intestinal diets usually contain rice as rice is
more digestible than other grains. You are discouraged from administering
over-the-counter diarrhea medications without first consulting a
veterinarian. If the pet is active, not dehydrated and has been previously
healthy, acute diarrhea can often be managed at home. Diarrhea that
continues for more than a few days or is accompanied by depression or other
signs is an indication to take your pet to a veterinarian.
Diarrhea of large intestinal origin can be caused by whipworms, polyps,
inflammatory bowel disease, colonic ulcers or colonic cancer. Stress can
cause large bowel diarrhea in excitable dogs. The diagnosis of large
intestinal diarrhea is also made by blood tests and examination of the
stool. A rectal examination using a gloved finger may provide some
information about the cause of large bowel problems including rectal polyps
and rectal cancer. Endoscopy to examine the large intestine is performed
using a rigid or flexible scope passed up the rectum. Because the rectum is
often very irritated, colon exams are usually performed under general
The treatment of large bowel diarrhea may be based on a specific
diagnosis. Non specific treatment of large bowel diarrhea often includes a
high fiber diet and sullfasalazine, an anti-inflammatory drug.
Washington State University assumes no liability for injury to you or
your pet incurred by following these descriptions or procedures.
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