The diagnostic lesions of FMD in cattle are single or multiple vesicles ranging in size from 2 mm to 10 cm. These lesions can occur at all sites of predilection.
Fluid fills the area and a vesicle is formed.
A grey, fibrinous coating forms over the eroded area. This coating becomes yellow, brown, or green. Instead of vesiculating, the fluid is apparently lost as it forms, and the upper layers of the epithelium become necrotic and discolored. Then the lesion appears necrotic rather than vesicular. On the Feet-The vesicle in the interdigital space is usually large due to movement and weight.