If someone is trying to provide ALL their own chicken feed, those grains can be very important as a source of calories. Chickens do need a certain amount of energy each day, provided by either carbs or fat. But it is impossible to make a suitable chicken diet from only grains, so they definitely need other things too.
Chickens need plenty of protein as well, and that is often more expensive, and harder to store. Bugs are one source, fish are another, soybeans and other beans are also sources, and actual meat is another source of protein. For example, if someone hunts deer, they might feed some of that to the chickens (especially the parts the human doesn't feel like eating.)
Protein needs to include the right balance of amino acids. That can be done with analysis and supplementation. This is typically needed if the protein is coming mostly from plant sources. Or you can do what people did about a hundred years ago, and use actual meat (including fish, bugs, and maybe dairy products.) Those tend to have the right amino acids in proportions that work fairly well for chickens, so it saves a lot of figuring at the cost of using more expensive ingredients.
Vitamins and minerals are needed in smaller amounts, but are very important too. Free-choice calcium (usually oyster shell) is easy to provide. Other vitamins and minerals are found in grains, green plants, meat & other protein sources, etc. Different foods provide different vitamins and minerals. Chickens that forage over a wide area of ground might be able to balance their own vitamin & mineral needs, or they might not. Some areas of land are deficient in certain minerals, and the plants that grow on that land are also deficient, so any chicken foraging on that land would be deficient too.
If you plan on buying supplements, consider whether those would be available when you need them. Some things, like oyster shell, can be stockpiled to use later (the calcium isn't going anywhere, no matter how long you store it.) But some kinds of vitamin supplements cannot be stored very long, because the vitamins degrade with time. There's no point in adding a "vitamin supplement" that no longer has the vitamins!
Storing things like grains and protein sources requires that you protect them from bugs and rodents, and they also degrade in some ways over time. So it can be fine to store corn in the fall to feed in the spring, but I wouldn't try to store it for 5 years. And of course perisables (like fish and meat) need to be dried out, or frozen, or canned, or sourced fresh as needed.
Start with the basic idea that they are omnivores. So they eat animal-based foods and plant-based foods. They need plenty of protein, enough calories, and a variety of other things. A reasonable chicken diet might look a lot like a reasonable human diet, but without the fat/sugar/salt we usually add to make things taste "better."
), I just need to get a better understanding of what they need, and see if I can make that work with what I have around me.
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