Because: 1 additional feed.2. If overcrowded they will fight, and Hens etc are really mean to each other...will kill a sick or injured one.I have Ducks n Hens,.I LOATHE killing them, I can at least say I know they have a good life etc,.but I hate it...when you have reared from Ducklings its even worse. All that said I NEVER kill them infront of each other, nor would I let it run in front of flock...they are intelligent and I believe it upsets them.Exactly..pain receptors are in the brain.
Also, why butcher them because of the cold? They would have been okay.