From the heels, the hoof wall turns inwards, running towards the frog. These are the hoof’s bars. Look at them closely. They should begin with the heel at the level of sole, running in a downward slope.
Overgrown bars are painful for the horse (imagine that pressure on your feet). They’ll push up, into the sole, and cause flares in the hoof wall. They’ll crush, spreading outwards into the sole.
After you’ve trimmed away the dead sole around the bars, you’ll see if they’re functioning properly. They should bear partial weight. Only the rear of the bars should make contact with the ground. At the back, trim them to the level of the heels. Then, using the tip of your farrier knife, slowly scrape away at the bars, sloping them downwards to their finishing point.
Look carefully and you might find the bars are overlaid. They can be difficult to spot, as they’re crushed in with the sole. Trim this away carefully over time. Slowly, as the hoof recovers and expands, they’ll stand proud above the level of sole.