Small Intestinal Bacterial Overgrowth in Dogs

Certain bacteria need to be present in the intestinal system to enable the digestive system to do what it was created to do: digest food and enable the absorption of the nutrients needed by the various bodily systems from the food ingested.  This is the function of intestinal bacteria in all species, including canine and human as well as nearly every other species on the planet.  The wrinkle in the fabric occurs when something causes the normal bacterial types to proliferate and become unbalanced.  The resulting condition is small intestinal bacterial overgrowth or SIBO.

Small intestine bacterial overgrowth in dogs is defined as an overgrowth or imbalance of the normal intestinal bacteria which are needed for digestion and absorption of nutrients from food.

The symptoms of small intestinal bacterial overgrowth (SIBO) as probably just what you might expect (for the most part) but also there are symptoms on this list which might surprise you:

• Gas
• Diarrhea - more chronic, lasting weeks or months
• Weight loss despite ravenous appetite
• Constant hunger or anorexia
• In young dogs, stunted growth and failure to thrive, despite increased appetite
• Vomiting - chronic in nature as a rule

SIBO doesn’t always present with all of these symptoms but the ones being exhibited by your pet will likely be more chronic than sudden or sporadic.

Types 

Small intestine bacterial overgrowth in dogs is considered one of several types of malabsorption syndromes found in small animals. Malabsorption is defined as a “defective uptake” of dietary nutrients due to interference or other interruption in the digestive and absorption process or as a result of disease of the small intestine.  Here are three types (or categories) of malabsorption syndrome mechanisms:

• Luminal - Caused by a lack of pancreatic enzymes
• Mucosal - Caused by mucosal damage, inflammation, lactase deficiency - this is the category into which SIBO falls
• Postmucosal  - Caused by lymphatic deficiency and obstruction with impaired delivery of enzymes and other organisms

Normally, food enters the stomach where the digestive process begins.  The upper portion of the small intestine has the job of continuing the digestive process, catching the food as it comes from the stomach.  The small intestine is also responsible for beginning the process by which nutrients are extracted and absorbed into the bloodstream for use by the various body systems.  Bacteria in this area work to break down the partially digested food for the absorption process.  The problem occurs when the bacteria overgrowth (SIBO) is such that the balance of the bacteria prevents this step in the digestive process from occurring as intended.  Here are some of the reasons why this condition occurs in dogs:

• Ileus - Neurologic problems, gastrointestinal obstructions, pancreatitis, peritonitis, parasitism are conditions which can inhibit the normal forward movement of the food called ileus
• Altered digestion or absorption of nutrients - Less than adequate secretions of pancreatic digestive enzymes and other disorders contribute to this deficiency in digestion and absorption of nutrients
• Malnutrition or immunodeficiency - These conditions erode the body’s overall condition which affects the body’s defenses, allowing the bacteria to grow unchecked

Diagnosing small intestinal bacterial overgrowth is not necessarily a simple process.  This is the case because the symptoms and many of the clinical signs are quite similar to many other health conditions and diseases which are common to canines.  Your veterinary professional will need a complete history from you, noting what symptoms and signs you have noticed, the severity, frequency and duration of each of the symptoms as well as dietary regimen and any changes made in it (if any) and changes in behaviors and symptoms which may be consistent with those dietary changes.  Your vet will need to do a thorough physical examination, complete with abdominal palpation and rectal examination, regardless of whether large intestine involvement is suspected.  

Fecal and urine samples as well as blood testing will also be required to obtain correct and accurate diagnosing.  Identification of any underlying disease process or condition will be a primary concern during the examination process by your vet.  He will need to determine what, if any, underlying diseases or conditions are present as they will need to be treated right along with, or perhaps even before the small intestinal bacterial overgrowth is treated.   Ultrasonography and radiography may also be employed to isolate and accurately diagnose the root and cause and any underlying contributors to the SIBO.

Treatment of small intestinal bacterial overgrowth (SIBO) in dogs will be dependent upon the cause of the condition as well as any underlying conditions which may be contributing.  The treatments for SIBO, after considerations are given to the primary cause (if known), will consist of dietary regimens and management of any complications.  For example, diets consisting of low fiber with moderate amounts of fats may be suggested for pancreatic involvement causes, or, a diet which is low in fat may be recommended for small intestinal diseases.  These dietary recommendations would be made to reduce the diarrhea and aid in the digestive process.  Antibiotics administered orally may be utilized for a period of time to help owners manage the clinical signs.  

This type of SIBO is called ARD (Antibiotic Responsive Diarrhea) and this regimen has been found to be successful in many dogs and a variety of breeds (this condition is common to German Shepherd breeds). Of course, when the SIBO is secondary to another underlying, undiagnosed and treated disease, it can be more easily managed as the underlying disease is also treated.  Sometimes, depending on the underlying cause, the SIBO may take a less than number one priority position until the underlying disease is treated.

While there are cases in which the veterinary professional cannot determine the cause of the small intestinal bacterial overgrowth, the condition can still be treated.  This is called idiopathic SIBO and most generally responds to antibiotic therapy.  The important thing to note here is that, for idiopathic SIBO, the dietary and supplemental treatments may be required long term.  For those young dogs suffering from an idiopathic condition, many of them have been known to outgrow it.  Another important fact for owners of canines afflicted with chronic SIBO is this: chronic SIBO can cause permanent functional damage to the intestinal mucosa.  This fact explains why some dogs respond positively to treatment while others require lengthy, if not lifelong, dietary and supplemental regimens to manage the conditions.  

The malabsorption of nutrients can literally cause your canine to starve to death despite ravenous appetites, thus, if this condition remains untreated or isn’t properly monitored after successful treatment, your canine’s prognosis decreases.  The best advice which can be given is simply not to ignore or “blow off” chronic episodes of diarrhea or vomiting, weight loss and appetite changes.  Get your vet involved early on to ascertain the cause of these symptoms to avoid irreparable damage to your beloved doggy family member.