When you keep them a stallion then they fully develop their body, unlike when you cut them while they are still a yearling. You should read up on what testosterone can do to the body xpp and what effects it has on a growing one.
He still has spunk, it's just that I don't have to deal with.. well, what stallions do when they see a mare anymore. Kind of, when he was in his studly stage he wasn't really thinking so you have to teach them to think and not just go off of instinct. It's just another thing you have to get over when training they don't loose their personality just the part that makes them crazy Zp