The "deep litter method" (DLM) is a method that was used in chicken coops by families, farms and breeders for decades and decades. It's an age-old wisdom and is nature's finest sanitary process. There's a couple of generations in between this more traditional form of keeping a coop and the modern industrialized method which is less humane and effective. Our birds, people and the environment all benefit by using the deep litter method.
The modern industrialized method of keeping a coop involves the use of chemicals for sanitation and frequent "cleaning". Bedding is changed out often, and coops are sprayed down to kill germs. This is not only time consuming, but actually less clean.
The deep litter method involves using a deep layer (6 to 12 inches) of bedding (pine shavings are most popular) inside the coop which will become a "living entity" unto itself. After about 3 months of your flock using this same litter, a very slow burning form of composting will begin taking place inside the coop. Birds will deposit their droppings in the bedding and then it needs to be turned. You can turn the bedding yourself, but it's easier and more fun for the birds if you throw some treats in there for them and watch them eagerly hunt and scratch for it while turning it for you (and them). The droppings then fall toward the bottom and in combination with the bedding, a slow composting begins. In essence, it works on the same principle as your backyard composter - the pine bedding is the "brown layer" and the bird droppings are the "green layer". Turning is done by the birds. Because the bedding is absorbent and composting is taking place, your coop will not smell. If you ever smell ammonia, it means you don't have enough ventilation (or water is leaking in coop) or you need more bedding added. You will only need to replace and deep clean once or twice a year! If you clean it more frequently, ironically, it will be less "clean" as you will interrupt the composting process. When cleaning is done in the coop, make sure you don't remove all of the old bedding. You want to leave a layer that is actively at work so when you add the fresh bedding, the process will start working quicker.
A second benefit of the DLM is you can take everything you shoveled out of your coop when you decide to clean it or if it gets too high and use it as compost. Remove the old bedding from the coop when time and make a compost pile out of it in the yard for any fresh droppings that are not fully composted (chicken manure has a high nitrogen concentration and can easily burn plants if not composted). Many people like to clean out in Spring so they can use this wonderful compost for their Spring and Summer gardens.
A third benefit to the DLM is that it's better for the birds' health. Since their litter is essentially alive while composting, the birds have a constant source of vitamin B12 which is created through bacterial fermentation. So, when you throw down their treats and they are turning their litter, they are also ingesting a lot of B12. Studies done in the 1940's showed that many chickens on an incomplete diet living in a deep litter coop remained just as healthy as birds eating a complete diet in a non deep litter coop. Also, with the DLM, chicks and chickens will be exposed to very low levels of Coccidiosis which helps build their immune system resistance to this disease.
So, with all this said, what a beautiful system!! Feed all your kitchen scraps to your chickens, they'll do the composting work for you, give you beautiful eggs and you get to use the compost later for your garden all while keeping a cleaner coop and having healthier chickens. Some good things should just be left alone, huh? Nature has perfected this cycle.