Diarrhea is one of the most common complaints pets are brought in for our veterinarians to evaluate. Understanding how diarrhea occurs will help you prevent and treat this condition in your pet. Diarrhea is caused by three major mechanisms:

  • Poor digestion in the small intestine
  • Poor water absorption in the colon
  • Motility problems.

When you or your pet eat, food is broken down mechanically in the mouth and stomach. Enzymes from the saliva, acids in the stomach and enzymes in the small intestine, help to break down the food into a very wet slurry. Nutrients from this slurry are absorbed in the small intestine (jejunum and ileum). If food is not digested properly, the particles will move through the intestines and act to draw more water into the intestine.

As the slurry passes into the large intestine, the majority of water is reabsorbed into the bloodstream to be recycled and the stool is formed into firm logs.

If the food is not properly digested in the small intestine, the amount of material presented to the colon surpasses the colon’s ability to absorb the water. This results in watery diarrhea with larger volumes than normal. This type of diarrhea may have a very foul odor and be associated with a lot of gas, as the undigested food is then broken down by bacteria in the colon to form gas. Generally, we don’t see blood or mucus associated with small intestinal based diarrhea. Causes for this type of problem include:

  • Food that is indigestible
  • Ineffective pancreas function and thus a lack of enzymes to break down the food
  • Inflammatory bowel disease in which the intestines are inflamed and thus not absorbing nutrients properly
  • Parasites which cause inflammation and poor absorbtion
  • Viruses which impair absorption like parvovirus
  • Cancer of the intestine which impairs its function.

The colon acts to dry out the intestinal slurry to form normal stools. If the colon is inflamed, this process is impeded and the stool is released prematurely while it is still wet. When the colon gets inflamed, the cells of the colon secrete mucus in an attempt to protect themselves.

Frequently there can be capillary bleeding which results in red blood and mucus on the surface of the stool. The inflamed colon is often painful and may lead to an increased sense of urgency for your pet. This results in frequent stools with smaller volume than we typically see with small intestinal diarrhea. Causes of large intestine or colonic diarrhea include:

  • Irritating intestinal contents such as rocks, garbage etc.
  • Inadequate fiber in the diet
  • Inflammatory Bowel disease
  • Stress induced colitis
  • Parasites
  • Viruses and Bacterial toxins
  • Inappropriate bacterial colonization
  • Cancer

The intestines contract in a regular fashion which helps to break down the food and to move it through the intestines. This process is called peristalsis. If the rate of peristalsis is altered, the intestine may not have enought time to absorb nutrients (small intestine) or absorb water (large intestine). Many factors affect the motility of the intestines includine:

  • Stress
  • Viruses
  • Bacterial toxins
  • Foreign bodies (the body increases the rate of peristalsis in order to try to move the foreign body through)
  • Drugs (some slow the peristalsis such as opiods like immodium, and some increase the rate of transit)

Understanding these basics, we try to characterize your pet’s diarrhea into one or more of these categories (yes, you can have both the small and large intestine affected) and then do the appropriate tests to try and find the actual cause. Typical diagnostic tests include:

  • Fecal Flotation to check for eggs of worms in the stool
  • Giardia test by in -house ELISA test
  • Parvovirus test
  • Radiographs of the abdomen
  • General blood chemistry testing and Complete blood count
  • Fecal Culture and Sensitivity to check for pathogenic bacteria such as Clostridium, Salmonella, Campylobacter etc.
  • Trypsin Like Immunoreactivity to evaluate the pancreas
  • Intestinal Biopsies

Our veterinarians will select the appropriate tests based on your pets history and symptoms. Treatment for specific problems vary with the actual cause of the problem. General symptomatic treatment includes:

  • Stopping food for 6-12 hours to give the intestines a rest
  • Feeding highly digestible food such as boiled egg and rice or Hill’s I/D intestinal diet (best for small intestinal diarrhea
  • Feeding increased fiber diets like Hill’s W/D diet. The increased fiber has an anti-inflammatory effect on the colon.
  • Drugs to reduce inflammation such as pepto-bismol, or Metronidazole
  • Drugs to slow the motility such as immodium or lomotil
  • Repopulate the helpful gut bacteria with products like forti-flora pro-biotic