You'll not believe me on this but the chickens really don't pay the pepper any mind, so no introduction necessary. 2 well rounded tablespoonfuls to a quart of feed. Of course, if you're chickens are choosey like Metella's, try it out on a single feeder first to see if snoots get turned up. Oh, and two caveats- mice will, like the best of chili-heads, develop a taste for cayenne so don't count on it for any kind of long term rodent ward and while cayenne may keep the general worm load on your birds down (along with garlic and pumpkin pith/seed), nothing replaces an honest to goodness deworming agent.
I'm of the same school of thought as AOXA: "If they all have a worm overload, that is something I am doing wrong, so only in that case would I treat. I try to create an environment that is inhospitable to overloads. Small amounts of worms are normal and harmless. It's the overload." I would add only one footnote- this philosophy only strictly applies to those of us who are practicing free ranging techniques. If you are limited to coop and run only, the challenges in keeping a balanced environment are much greater and my hat is off to those of you who manage your birds so well in that setting!
Birds taste buds dont register heat like ours do. I had parrots before and their favorite treats were hot peppers