The white line is the area on the underside of the hoof where the outside of the hoof wall meets the sole. Despite its name, the white line is actually more of a cream colour. White line disease (WLD) is an infection that causes progressive separation of the hoof wall. Although it may start at the white line, it actually wreaks its harm in the internal structures of the hoof.
Damage to the white line at the toe, quarters or heel creates an entry point into the hoof for fungus and/or bacteria that are commonly found in the natural environment, but go wild in the damp, dark inner reaches of the hoof. As the layers of the hoof wall separate, the infection spreads. In its early stages, white line disease is not painful, but if left to develop, causes severe lameness and, at its worst, rotation of the cannon bone.
“There is a great deal of disagreement regarding the causes,” said farrier Cole Henderson, who sees a lot of WLD in this Vancouver Island practice. “Historically, it was always seen as a sign of poor stable management.”