It’s not what your horse does after you give him a bath. It’s not how he gets fresh dirt on his back. It’s the natural rounding of the edge of the hoof that occurs in free-roaming horses and burros.
Here are two examples from the Virginia Range. The rounding of the edge eliminates what’s known as a ‘stress concentration’ in engineering work.
A sharp edge can be susceptible to cracks. Your farrier probably rounds the edge with a rasp when he trims your horse’s feet.
Next time he visits your ranch or barn, ask him about the mustang roll.