Often, diagnosis is based on the clinical signs of disease, and the horse's response to treatment.
A more definitive diagnosis requires identifying the small strongyle eggs within the feces, through a fecal flotation exam. Unfortunately, a horse may be harboring an infection for a significant period of time before the disease is detected through this test, because once a horse becomes infected, the small strongyle larvae will take six to 12 months to mature into adults and produce eggs.
It is not possible to distinguish a small strongyle from a large strongyle through a fecal flotation exam, so often a fecal culture may be performed as well. This procedure allows the larvae to develop, so that they can be evaluated under a microscope to determine whether they are small or large strongyles. Most horses have a mixed infection of both small and large strongyle parasites.
