I think you did the best you could in that situation.

I used to help out on a farm with chickens and if any chicks hatched deformed the farmer would smash it on the floor without a seconds thought.

Also my mate keeps chickens and if any of them becoming old and ill where they wont recover her partner just breaks their necks rather then let them die a lingering death. I guess its for the best really although I could never do it myself! I cant even kill a bloomin spider!