Antibiotic-responsive diarrhea in small animals.

Antibiotic-responsive diarrhea (ARD) is an idiopathic syndrome causing chronic diarrhea in young, large-breed dogs. Why antibiotics are effective in controlling diarrhea is not understood, and whether small intestinal bacterial numbers are truly increased is now doubted, but previous focus on the condition being small intestinal bacterial overgrowth has hampered the understanding of this condition. The name ARD simply defines the condition, and studies are now looking at the interaction of small intestinal bacteria and the mucosa to try to understand why it occurs.