Small Intestinal Bacterial Overgrowth (SIBO) in Dogs

While it’s true that certain bacteria must be present in the gut for digestion and absorption of nutrients to take place, if bacterial growth gets out of control, trouble ensues. That trouble is called, quite simply, small intestinal bacterial overgrowth or SIBO. The disease can occur for a variety of reasons and it can affect any dog. Gas and diarrhea are the major symptoms. Antibiotics can help quell bacteria overgrowth while underlying causes are treated accordingly.


The upper part of the small intestine is responsible for the continued digestion of food as it exits the stomach and for beginning the process in which nutrients are absorbed into the bloodstream for dissemination throughout the body. The bacteria present here normally aid in the process of breaking down partially digested food within the intestines. In dogs, the overgrowth of this bacteria results in a common process that’s descriptively labeled, “small intestinal bacterial overgrowth” or SIBO.

It’s a big problem for some dogs, and it occurs for several reasons including the following:

  • Ileus: When normal peristaltic waves moving partially digested food forward aren’t present, bacterial populations increase. Neurologic problems, gastrointestinal obstruction, pancreatitis, peritonitis, parasitism, and other processes can all cause the lack of forward intestinal movement called ileus.
  • Altered Digestion or Absorption of Nutrients: This can occur with exocrine pancreatic insufficiency (inadequate secretion of digestive enzymes by the pancreas) and other disorders that can lead to poor digestion and absorption of nutrients.
  • Malnutrition or immunodeficiency: When the body’s overall condition is adversely affected, all the normal defenses can break down, leading to uncontrolled bacteria growth.

The above tend to be labeled secondary causes of SIBO. But SIBO can also be idiopathic, which means veterinarians don’t understand exactly why it happens.

Symptoms and Identification

Secondary SIBO can affect any dog, depending on the underlying cause. But idiopathic SIBO tends to affect relatively young dogs. Diarrhea and flatulence (gas) are the most common signs of SIBO. Chronic, intermittent diarrhea is most typical, with many dogs also suffering weight loss, stunted growth, and/or generalized failure to grow or gain weight. Some dogs may appear inordinately hungry and may even eat their stools or other indigestible items.

SIBO is identified by noting small bowel diarrhea (characterized by limited straining and large volumes) and finding large numbers of bacteria in the fecal material. Diagnosis is aimed primarily at ruling out other potential causes of bacterial overgrowth and diarrhea. Because these are numerous, the process usually involves X-rays, serial fecal examination (not cultures, which are notoriously unreliable), and sometimes endoscopy to test the upper part of the small intestine for high bacteria counts.

Blood tests that reveal high folate levels and decreased cobalamine may also be indicative of the process. That’s because folate is synthesized by the bacteria, and cobalamine is bound by them. However, these tests may be inconclusive.

Affected Breeds

German Shepherds are over-represented among those who suffer with SIBO, but dogs of any breed can be affected.


Treating the underlying process is the approach best undertaken for secondary SIBO. For idiopathic SIBO, antibiotics are highly effective in helping owners manage their dogs’ clinical signs. That’s why this version of the disease is often referred to as antibiotic-responsive SIBO or antibiotic-responsive diarrhea (ARD).


For secondary SIBO, if the underlying cause can be addressed, the condition is more easily corrected. However, there is no cure for idiopathic SIBO. Some young dogs may seem to outgrow the condition (possibly as their immune system matures), but in other cases dietary therapy and supplements may be recommended to help manage the condition long term.

This article has been reviewed by a Veterinarian.

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