A disease affecting the horn in the region of the white line. The horn in the white line is generally softer than the horn in the adjacent hoof wall and it may be additionally weakened by diseases or disorders of the hoof such as laminitis. These factors contribute to the increased potential for the horn of the white line to become damaged due to mechanical factors (e.g., small stones that become lodged in the horn) or invading micro-organisms (e.g., bacteria or fungi) that lead to disintegration of the horn. White line disease is a progressive disorder that can lead to damage in the stratum internum or the innermost layers of the stratum medium of the hoof wall proximally to the white line. Damage can become extensive and cavities can be formed within the hoof wall. This results in an undermined hoof wall, a condition very similar to and often confused with seedy toe.