Vets euthanasia procedure

Hi there. I know this is a strange thing to ask but how do vets put chickens to sleep? I know what happens with cats and dogs but I was wondering if it was the same or if e.g. they are given a sedative first?

I know I couldn't perform the deed myself at home so if in the future this needed to be done with my girls I would rather know what to expect   

Hope you don't think this is a silly question....