What is a corn? Corns are bruises of the sensitive corium at the angle between the wall and the bars ("the seat of corn").   Corns can be: Dry – where the surface of the horn is dry but discoloured. Moist – where the horn over the bruised area is moist due to seepage of serum from the damaged corium. Suppurating – where there is a discharge of pus because of infection of damaged tissues.

The common causes of corns are concussion and leaving a shoe on for too long a period so that, as the hoof grows, the heels of the shoe move forward and off the wall and on to the "seat of corn".     Bad hoof structure can also be a predisposing factor, as in the case of a hoof that has a long toe and low underrun heels which create excessive pressure to the corium in the “seat corn”.