As for the herd sour issue, its something I deal with a ton in youth.. They seem to give more problems then adults and act up way out of what the expectations I have set for them! Drives me bonkers! LOL! I tend to play alot of the tying game with them when they are herd sour. This way I can start to bring them back down to their fits not getting them what they want, and not to mention, I dont have to expend all the energy to keep things in control while teaching them that they need to be more attentive to me. Of course I will also tie them off out of sight of the group they are having issues with.
If you are going to use the tying game, make sure to set their head semi-low. Right around wither height, this way when they start thrashing around they cant hurt themselves, and with their head setting lower, they dont learn to rear up as a reaction to their displeasure! LOL!
As for the reading litature.. John Lyons is one I know of that has soemthing about starting colts and what not.. I will say though, I havent seen too much put out about youth. Thats an area I have had to muddle around in quite a bit to get experience and an understanding on.
Dixon's Red Hot Ember