My chickens' favorite "treat" is their regular feed, wetted into a mash. It's your regular feed, silly birds! It's also a great way to use up the fine bits they won't eat that fall to the bottom of the bowl. I give them this every day; no worries about using it for a treat.
@AmyJane725, if you...
This is not an answer to your question, but it might be of help.
I cut a calcium citrate pill into 4 pieces. I put a bit of peanut butter on a piece, and the pullet I need to dose will eat it.
The very first time, she picked it up, dropped it, picked it up, ran off with it, dropped it, looked...