Some people feed their chickens all sorts of things to "improve" their health. Some don't. Some of the things people feed chickens is vinegar in the drinking water, yogurt or other thing that are supposed to help probiotics, special grains or vegetables, drizzle vegetable oil on the feed to give pretty feathers, ferment feed, just a tremendous list, much like what you see people eating for their own health. As long as you don't overdo it, these things won't hurt. The people that use them, whatever them they are using, will tell you how great they are and how much they help, but many people don't do any of those and have healthy chickens. Feel free to use any of them you wish, just do it in moderation. You won't hurt and you might help.