Two years ago I had an interesting case. A horse named Riley was chronically lame in his left front foot due to abscesses, a painful condition where pressure builds up the sensitive part of the horse's foot due to pus. The condition usually resolves on its own in a few days by finding the pathway of least resistance, either out through the coronary band at the top of the hoof or on the bottom of the foot along the "white-line.". The white line is the intersection between the sensitive and insensitive tissues of the foot.
Riley would abscess every month or so and be in excruciating pain. He didn't want to put any weight on his limb, and at approximately 1500 pounds this put a lot of stress on his other front limb. This went on for a year or so. The farm changed vets and I inherited Riley. He was not a good patient and was a bit of a big bully. The farrier didn't like him because he wouldn't keep his feet up to be trimmed. He was in and out of pain and it led to some unhelpful behaviors.
I recommended radiographs (x-rays) of his foot and we found some inconsistencies between the bone and bottom of his sole. Using the skilled farrier to pare out the abscess tract we came to realize that 80% of his sole was undermined by another sole underneath it. There were two soles separated by a layer of pus. The farrier carefully respected the sole revealing a moderately hard sole that had toughened enough to stand some pressure. We put a hospital plate on to give him support and protection.
At the thirty day recheck the new sole was hard enough to take the hospital plate off. Riley hasn't abscessed in two years!!