This is a term I do not know. From what I have been able to find out it is some type of neutering for roosters? How do you do this and will it make the intact roosters accept and not try to fight the "fixed ones"?
Culling simply means "to remove" from the breeding pool, from the flock, etc. One can sell, give away, or butcher for the meat. In any case, the bird is removed. To make a Capon is the neutering of a cockerel.