The sole and wall tend to wear flat due to the abrasive and shearing forces from walking on concrete. The cow becomes more cow hocked as she tries to relieve pressure on the rear, lateral claws. The claws also will splay because the abaxial wall is longer than the axial wall. This leads to uneven weight distribution and increased pressure on the corium especially near the rear of the pedal bone. If the pressure is great enough and prolonged enough then permanent damage is done.
Damaged corium produces damaged horn, which sets up a vicious cycle.
Functional Hoof Trimming A s mentioned above the hoof tends to grow at a rate of about 5 mm per month. The shape of the hoof is a result of a balance of growth and wear. The toe will tend to wear slower since it is harder and the heel will wear faster since the horn is softer. The goals of functional trimming are to distribute the weight evenly between the 2 claws of the foot, to leave sufficient horn to protect the corium, and to trim the claws to their normal shape and proportion. We are basically trying to create a flat surface for the cow to walk on that will minimize trauma to the corium.