Holly, the hen, had been fading all winter. Her comb turned pale. I tried worming her. I checked her for parasites. I had a fecal float test done. Nothing.
I began to suspect she had internal problems. She was our little chick that wouldn't grow and, at 9 months old, had never laid. Eventually she couldn't stand up. It was time to put her out of her misery.
The method I eventually chose was to use a killing cone and a sharp knife. A killing cone is a metal cone that restrains a chicken so that it can be killed. Since it was Sunday and I didn't want to go to the store, I made a cone out of a cardboard box. (One time use only). I clamped a piece of 2x4 to a ladder to suspend the killing cone from. I put a large garbage can with a trash bag in it under the killing cone. I put her in. I think she expired right then. To make sure she was dead, I cut her veins like you would for a meat chicken. I used a kitchen knife, but I learned it wasn't really sharp enough. Next time I'll use a filleting knife or a box cutter. Then I disposed of her body appropriately.
It was stressful, but I was glad she was out of her misery.