Pathomorphological findings in a case of onychomycosis of a racehorse.

The hooves of a racehorse which were affected with white line disease and hoof wall disorders on both forelimbs were histopathologically investigated using thin ground section and standard paraffin section techniques. On both hooves, large quantities of fungus were found to have invaded the white line tissues, especially in the terminal horn which were markedly damaged. The fungus was also present among the cellular debris in the fissures of horny tissues. The morphological characteristics of the fungus were brown (its natural color), PAS-positive, mold-like shape with septa inside the tissues, and unicellular spores outside the tissues. These findings suggest that onychomycosis was a primary and/or secondary cause of white line disease in this subject.