The white line can be found on the bottom of the horse’s hoof close to the edge as a lighter area of horn where the hoof wall and sole meet. Like any join or seam, it is a potential weak spot.
White line disease occurs when the external hoof wall separates from the underlying laminae, which hold the pedal bone in position. The horn along the white line becomes crumbly and soft. This can allow bacteria and fungi to gain entry and cause further damage. The disease can occur anywhere on the hoof, although the toe is most common area, hence the common name of seedy ‘toe’. While the outside of the hoof may appear normal, when tapped it may sound hollow when compared to unaffected areas.
Your farrier can manage mild cases caught early, which rarely cause lameness, during their regular visits. The biggest concern with seedy toe is that in severe cases, when significant lameness will be seen, the internal support of the pedal bone can be compromised, leading to movement of the pedal bone, similar to laminitis cases.
Which horses are most at risk?
White line disease can be found in all sizes, types and breeds of horse, although donkeys are particularly susceptible to it. Horses with poor quality hoof horn may be more likely candidates.