This horse has many problems but if you look closely you can see that his heels are very crushed and contracted. This can be a result of poor shoeing or some Thoroughbreds have a pre disposition to a problem. Sometimes allowing the horse to go barefoot will help.
See how these heels have no breathng room. This has to hurt!
This horse had been in training and at a race track from very young. The problem predisposes him for thrush and other ailments. This has to have been a chronic problem for him.