A 4-month-old female Siberian Husky was referred for a 2-month history of intermittent diarrhea, poor body condition, polyuria, and polydipsia. Based on the history, the diarrhea was thought to be of small intestinal or mixed origin because the dog had a ravenous appetite, poor body condition and failure to thrive, frequent defecations, and feces that occasionally were covered by mucus. The dog had been diagnosed with and repeatedly treated for hookworms and coccidia by the referring veterinarian with a combination of praziquantel, pyrantel pamoate, and febantel, a and metronidazole.b The dog also had been treated with amoxicillin, c sulfadimethoxine, d and prednisone e for short periods of time. Two weeks before presentation, the referring veterinarian changed the dog's regular diet f to a prescription diet g formulated for dogs with gastrointestinal disease. The antiparasitic medications, antibiotics, glucocorticoids, and diet change led only to transient responses, and the diarrhea always recurred with discontinuation of therapy despite the fact that both direct fecal examination and fecal flotation were negative. The dog's appetite was increased for the entire period of 2 months.At the time of presentation, the dog weighed 12 kg and was in poor body condition (body condition score 3/ 9; optimal, 5/9).1 Slightly thickened, gas-filled intestinal loops were identified by abdominal palpation. CBC and serum electrolyte concentrations were within normal limits. A serum biochemical profile revealed mild increases in alkaline phosphatase activity (ALP, 187 U/L; reference range, 10-150 U/L), creatine kinase activity (CK, 421 U/L; reference range, 10-200 U/L), and serum phosphorus concentration (8.8 mg/dL; reference range, 2.1-6.3 mg/dL), and a mild decrease in blood urea nitrogen concentration (BUN, 4 mg/dL; reference range, 7-27 mg/dL). Liver disease was suspected, and fasting and 2-hour postprandial total serum bile acid concentrations were evaluated and found to be normal (fasting serum bile acid concentration, ,1.0 mM/L; reference range, 0-5 mM/L; postprandial serum bile acid concentration, 1.5 mM/L; reference range, 3.9-12.7 mM/L). A relatively low specific gravity (1.017) was noted on urinalysis, and bacterial culture of urine yielded no growth.Radiographs of the abdomen were normal, but the layers of the small intestinal wall could not be differentiated on abdominal ultrasonography, and a prominent pancreas of normal echogenicity was identified. Serum concentrations of cobalamin, folate, canine pancreatic lipase immunoreactivity (measured as Spec cPL h ), and canine trypsin-like immunoreactivity (cTLI) were determined and results of these tests were Spec cPL ,29 mg/L (below the detection limit; reference range, 29-200 mg/L), cTLI 7.1 mg/L (reference range, 5.0-35.0 mg/L), cobalamin 1,001 ng/L (reference range, 249-733 ng/L), folate 39.3 mg/L (reference range, 6.5-11.5 mg/L). These findings were interpreted as consistent with small intestinal bacterial overgrowth (SIBO), also referred to as antibiotic-responsi...

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