From what I hear....cull bucks I'm assuming are "management bucks" bucks that by 4.5 or 5.5 don't show much potential to be big boys, so they take them out of the breeding population.

Funny thing though, a study I read showed that the majoirty of bucks that are breeding the most are 2.5, 1.5yo, after 2.5 they numbers started to fall off the table, therefore....that buck that's being culled at 4.5...has already passed on his genes to tons of does....

But it was a surprising study since it was have thought that the older bigger bucks would have done the majority of the breeding. With that being said I think you almost need to get those lesser bucks out of there by 3.5....if you can, not sure that taking some 2.5yo as management bucks are possible though since it could just be young/small, not genetically small....

I would try though to in my area if I were managing, pass on those giant 2.5yo....to breed, and take out the lesser ones.