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What we are talking about is Purina brand Flock Raiser. It is a grower feed for various kinds of birds of various ages. It does not have the extra calcium that "layer" feed has in it for the hens to produce eggshells, that is why we supplement with oyster shell on the side, free choice so that only the hens who are laying have to eat it. Too much calcium is not good for younger birds.
Something a local feed store makes themselves will not be the same thing, although it could be based on the same idea. You will have to figure out what is in it before you will know if you need to supplement something, but if it has a good reputation among other chicken keepers then it's probably good stuff.
Personally, I always offer free choice oyster shell, no matter what type of feed I'm using, because it's a cheap way to ensure that they have enough of what they need.