Sporting answer: Fitting bits to poults
A) It depends on how many birds you are going to put in the brooder house. If you are only going to rear 100 or so, they will probably be fine without being bitted, but any more than that and I would advise you to bit them when they are about three weeks old, just to be on the safe side.
It can be tempting to leave them unbitted, especially if they look feather-perfect at three or four weeks old, but to do so would be a mistake. A couple of wet days, when the poults are standing about bored, is sometimes all it takes for them to start featherpecking, and they can quickly lose the protective feathers on their backs.