I've had to cull only a handful of chicks. I've only culled when I believed what ever was wrong made them incompatible with living or living within a flock. I've had one with splayed legs, one with all kinds of inside stuff hanging out the vent and one with foot problems. Another that was dieing slowly as well and one that had an upside down head. I believe all the issues I have seen to be related to incubation. The one issue I didn't experience in my home built I believe to just be a fluke of nature. My husband typically axes them. He did think that dropping something heavy on a chick might have been easier only to discover removing the head was easier and less of a mess. I think the cute chick factor makes it harder.