Malabsorption and Bacterial Overgrowth in Dogs

What is malabsorption and bacterial overgrowth?

Small intestinal bacterial overgrowth (SIBO) is a condition of the small intestine that results in increased numbers of bowel bacteria, leading to diarrhea. This condition has more recently been termed antibiotic-responsive diarrhea (ARD).

The bacteria cause damage to the absorptive surface of the bowel so digested food cannot be absorbed through the bowel and into the body, resulting in malabsorption of nutrients. 

Malabsorption due to other causes can lead to a secondary SIBO, as the increase in undigested nutrients act as food for the bacteria to proliferate.

Malabsorption and SIBO both result in diarrhea, like that associated with enteritis (inflammation of the intestines). However, with bacterial overgrowth, the diarrhea is chronic, often lasting weeks or months.

Are some dogs more susceptible than others?

Affected dogs are most often young to middle-aged, large-breed dogs. German shepherds appear to have a higher incidence of malabsorption problems. These problems are frequently associated with exocrine pancreatic insufficiency (EPI), but SIBO can occur with or without EPI. See handout “Exocrine Pancreatic Insufficiency in Dogs” for more information about this condition.

What are the common clinical signs of malabsorption?

The principal sign of malabsorption is weight loss with chronic diarrhea. Most dogs will have a normal or increased appetite but continue to lose weight. Increased gas leading to flatulence and bloating are also commonly noted.

Can malabsorption be differentiated from pancreatic insufficiency, based on the symptoms?

Dogs with SIBO often do not have an appetite as voracious as dogs with EPI and usually have diarrhea that is not as voluminous as with EPI. With both EPI and SIBO, routine blood and urine testing is often normal. Affected dogs with both conditions may have low vitamin B12 (cobalamin) and folate levels, as they are not properly absorbed. A specific blood test called TLI (trypsin-like immunoreactivity) is used to differentiate the two conditions.

What is the cause of this condition?

Many cases of malabsorption are idiopathic (unknown cause). SIBO is frequently associated with exocrine pancreatic insufficiency (EPI). It can also be associated with inflammatory bowel disease and other conditions that disrupt motility or prevent absorption of nutrients.

Can the condition be cured?

Many cases respond to long-term antibiotics. Common antibiotic choices include Tylosin (Tylan®), oxytetracycline, and metronidazole (Flagyl®) for 4–6 weeks, usually combined with a special diet to treat this condition. The addition of probiotics (beneficial bacteria) and prebiotics (food source for the beneficial bacteria) can be helpful in many cases and may provide an alternative to long-term antibiotics. In cases of primary SIBO without any complicating factors, the prognosis is usually good, though recurrences are possible.