Actually, I beg to differ...if done properly with CO2, they do not slowly suffocate. I know this for a fact from my own use with my sick birds.Just a note on the dry ice...the chickens don't fall asleep with it, they actually suffocate as they run out of Oxygen to breathe. It is not as "humane" as decapitation. Everyone has their own preferred method, but those who prefer not to do it themselves are better off finding someone else to do the deed. I still cry when I walk past the spot in the yard where our rooster is buried. Fortunately I've found someone that will take all my extra cockerels, but the sick ones still have be dealt with,
Also, my husband works in electronics and they have CO2 systems that dispense fire. Protocol is to get out immediately with the warning bell before the CO2 release as you will be unconscious with the first breath, dead within minutes...the natural instinct is to gulp the gas at first exposure, fill your lungs, the shock to the cortex occurs immediately, you become unconscious and then asphyxiate within minutes. I have had firemen confirm this fact with CO2. The American Veterinary Medical Association also concurs. (Long read...look at page 15 and onward at https://www.avma.org/KB/Policies/Documents/euthanasia.pdf) And yes, I do realize that CO2 use is controversial for some with varying reports as to the effects...note that most of the reports are subjecting birds to slowly increasing levels of CO2 while they are held in chambers because in commercial purposes, it is impractical to fill the chamber, then submerge the bird due to risk to humans.
I am only dealing with one bird and one small bucket. The trick is to create sufficient CO2 concentration BEFORE placing the bird into the container. I can use dry ice because I have such a small area to fill, I can assure adequate concentration. Let the cloud of gas build with lid slightly ajar to prevent too much pressure build up, then lower the bird into the thick cloud of gas, close the lid quickly. They gulp (which may or may not create momentary mucus irritation...the ax or the stun would create momentary irritation as well), then lose conscious, and in my experience stop fluttering in a matter of less than 30 seconds...secondary muscular convulsions as they are already dead. j
Anyway, that's been my experience. Culling is always a difficult and unpleasant job, but sometimes it just has to be done.
Sorry for your loss of your favorite rooster. I'm sure he had a happy life in your coop.
Lady of McCamley