The trim we use is a refinement of all the knowledge we have found from around the world on hoof shape and function as well as the newer Bio-Mechanics that are currently being developed.
The most important factor in our trim is leveling the pedal bone to correctly align it with the leg and line of motion. IE the pedal bone must not unbalance the leg in all phases of motion or stationary. This is called Bio-Mechanics and Bio-Statics.
There has been much discussion around the world on what is the correct alignment for the pedal bone. The answer comes from the foot itself. At maximal load it must be level with the ground or the bone will remodell to distribute the energy load over a greater part of the bone rather than one perimeter region.
Farriers expect the pedal bone to sit at 8-10 degrees positive tilt. This is partly due to old studies that are based on shod horses over the years. After the barefoot studies of wild horses it was determined that a horse should have zero or close to zero palmar angle of the pedal bone. These are very hard feet with little general flexibility, the average domestic horse needs a palmar angle around 2-3 degrees. This is due to feet being more flexible and less developed than the wild horses. These feet at full load will flex enough to bring the pedal bone level with the ground.
When the pedal bone is at full load the circulation of blood under the bone is equal. A bit like a flat board on a water bed the fluid is loaded equally and the board stays on top equally. Like the board on fluid if the pressure is off centre it will sink below the fluid at whatever point has the higher load. The bone will remodel IE: structurally change to bring whatever part of the bone that goes below that flat bone back above it. If the bone is tilted in its loading with the ground the excess pressure will force blood away from the lower part starving it of nutrients. This poorly supported bone will erode away and stabilise at the level of the true sole plane. In concert with this bone loss you will also get thinning of the horses sole as the horses weight both abrades the sole and restricts blood flow to replenish sole.
Trimming this way is trimming the entire foot to the soles true plane. This is done by matching the collateral groves for depth and then matching the toe length to complement the collateral groves. This ignores the current visible sole plane which can be very wrong. Brian Hampson who has been studying wild brumbies has documented variances in sole thickness from hoof imbalances. The variances in wild horses can be greater than 25% of the soles thickness due to loading and blood flow.