The horse’s current hoof form is not allowing him to grow a healthy The markup shows the approximate location of the coffin bone and what it’s doing to the tissues and vessels in the foot.
Reported problems include very little hoof growth, very thin soles, and very little heel to remove. In reality there is a great deal of heel here that needs to be removed (as per markup). Its height is pathologically displacing the coffin bone. This orientation is the reason for the lack of hoof and sole growth, and the laminar wedge. The tip of the coffin bone is pointing down onto and compressing the circumflex artery, the only blood supply to the sole which is responsible for the thin soles and poorly growing, crumbly walls, and the front of the coffin bone is pressing on the sole. Pressure prevents growth.
At 4 mm, the soles are actually only 1mm less than the thinnest recommended amount (5mm), the issue is more the sinking of the bone onto the sole. As long as the circulation is compromised by the pathological orientation of the coffin bone, the laminae cannot reconnect at the top between coronary band and top of P3.
The tip of P3 at the extensor process is also being pushed against the blood vessel that would supply the blood to the laminae. The downward pointing tip of the coffin bone causes the laminar space to be much wider at the bottom than at the top; as long as this condition exists, the laminae will not reattach in a healthy fashion and rotation and a laminar wedge will continue to be present. The laminar space at the bottom needs to tighten up to the same width as at the top, so that the laminae are not stretched and torn beyond their natural capacity and continue to secrete blood and inflammation. This needs to be done by lowering the heel to where the blue line is.
Whenever we take his excess heels off, how do we keep his heels from getting underrun?
Underrun heels are defined by comparing the heel tubule angles to the toe wall tubule angles. They should be parallel. If the tubules converge (in the lateral view) from their starting point at the coronet towards the toe, they are underrun. Harder hoof wall is less prone to being crushed into this geometry so the horse with genetically harder feet is better off to start with.
There are specific trimming techniques for preventing heels from becoming underrun, if the horse is left barefoot. In general, the heels would be trimmed frequently (in this case, perhaps once a week), bringing them back to line up with the widest part of the frog. Then, one would also relieve, or float, the quarters very slightly under the heel area to prevent the tubules from being crushed by the weight of the leg and start running forward.
It’s also essential to keep the toes as short as possible to avoid drawing the heels forward as the toes grow forward. Maximum turnout is also helpful to prevent ammonia from weakening the tubules and allowing them to become crushed.
Since heels and toes thus predisposed need frequent management to prevent them becoming underrun, and shod feet are not trimmed more than every four to six weeks, I don’t know how one would prevent this from happening in a shod horse. Perhaps an experienced farrier would like to add their input on how to successfuly deal with that issue.