The Proper Way to Bit a Colt.

Farmers often put bitting harness on a colt the first thing they do to him, buckling up the bitting as tight as they can draw it, to make him carry his head high, and then turn him out in a field to run a half-day at a time. This is one of the worst of punishments that they could inflict on the colt, and very injurious to a young horse that has been used to running in pasture with his head down. I have seen colts so injured in this way that they never got over it.

Fonte: Tamming Horses