A loss of continuity of the horn wall originating from the bearing edge characterised by a loss of substance.The damage may start as a grass crack and progress to a defect or it may be due to a trauma such the loss of a shoe. If the damage is limited to the outer layers of the hoof wall this results in a frayed appreance of the hoof wall, damage to the entire thickness of the wall leads to a 'gap' in the distal border. The cause of this type of damage is frequently the result of an error in nailing (too large or misplaced nails) or an excessively long shoeing interval.