The only thing I have failed at is 2 rabbits I have, that no one in their right mind would have held onto. Its a long time I should have killed them. I'm too frugal to let too much time pass without slaughtering.
It isn't a pleasant thing for me, but I make myself do it. It might take a few hours for me to do 7 birds, esp if I'm working alone, but if I do that everyday for a while, then after a while, I really have a high profit farm project. I might be in the habit of putting a certain amount of food down, and when I've killed and killed, I see in the afternoons that the birds didn't finish all their food and I realize Its time to decrease their daily rations. Makes me happy, happy, happy.