It doesn't ease the heartache, but it does become easier the more you do. I grit my teeth and pray over them every time I slaughter beautiful, healthy cockerels I've hatched and raised for the freezer. Also when I cull the oldest (2-3 year) hens, even when still healthy and occasionally laying, to make room for new vigorous pullets. My goal is lots of eggs and lots of meat, so....Really sucks tho, having an otherwise fully capable and seemingly happy hen who will be killed by the same hands she trusts to hold and care for it. Ugh!!
They trust me so much, and that's the hardest part. The boys are still youngsters and see me as their mother. The girls have given me lots and lots of eggs, chicks and entertainment. When it's time to cull, I just talk to them, pet them, and keep them calm up until the final moment, then get it overwith as quickly and as humanely as possible. The heartache eases quickly once the deed is done, though.
My husband helps more than he knows. He doesn't mind the machete method, and quickly dispatches the old hens I hand over to him when I'm thinning the flock. It's easier with a sickly hen, because I justify it to myself as a mercy killing so they won't suffer. I do the cockerels myself at slaughter time with PVC cutters and a killing cone.
It's a daily reminder to myself that they are NOT pets, they are FOOD. And I take pains to make sure I don't get attached (except to my breeding roosters all of whom have names and get petted and talked to every night). I rarely have to cull a rooster, so I channel my maternal instincts and affection onto them while trying to ignore the rest of the flock.