I used to help this old man when I was young. One day we were sorting his yearling calves for replacements and he chose out one that was really nice looking but was wild and very aggressive. I told him that he was crazy to save that one.. he swore that he could get her as gentle as a lamb. We ran her through the head gate and he put a halter on her, tied it to a post beside the gate, and let her out. She bucked and tried her best to rip the barn down. I remember laughing and telling him that he was going to be the one to take the halter off. He said nope you're going to in a week or two with no trouble. He left her tied and feed and watered her right where she was. Sure enough in 2 or 3 weeks, we were able to lead the heifer around like an old draft horse. She never again was a bit of trouble. I've often thought about doing this to some of my wilder heifers that look good, but I've always just culled them. I don't have much experience with show cattle but I think this may be a common method of gentling them. The old man told me he had even done this with older cows with success.