Hi Mehmetkaya, I follow natural based health systems for myself and also for my flock. I think in nature animals are healthy when all is in balance. When chickens are in a restricted area, that can alter the balance. I try to correct for this by exposing them to healthy microorganisms through fermenting feed and composting piles in the yard and the deep litter method in the coop. Try to give them as much space as possible, at least during the day, this reduces stress on them and makes for much happier birds. Look at the threads here about fermenting feed, deep litter, and also about natural supplements now being used. I have learned so much!!
Oregano is a big one, garlic, cayenne pepper, in your area maybe one to try is Nigella sativa seeds - black seed, is known for being very beneficial for humans, but I do not have any experience with this for chickens.
I mix my own feed with a pea/ wheat base and add kelp, fish, crab meal, and azomite, dried and crushed nettles and alfalfa, lots of garden greens and lots of ranging area in the summer. You might have whole mineral supplements in your area that can supplement in the same way as azomite and kelp...both supply trace minerals.
There are lots of threads here that have lots of information about natural methods. I like to google around for studies that back up the ideas presented, both for me and for the flock. The area of nutrition and health through whole food sources is a big one and very popular, so a lot of studies being done.
