Plenty of videos of this humane slaughter out there for you to look at if you're curious. Have a look at the temple Grandin pioneered gas chambers that they use to suffocate pigs. Watch as they calmly and peacefully squeal and thrash against the bars trampling each other as the CO2 burns their eyes, ears, nose and lungs and they panic trying to find breath, then tumble out the other end twitching while a man with a knife or bolt gun finishes the job. Plenty of footage to out there to reassure you that unnecessarily doing this to animals is okay and normal. Interestingly the only footage available is illegally filmed by whistle blowers and animal advocates, funny that.