What is the best feed for adult roosters? They are NOT housed with hens and layer feed is said to be bad on their kidneys due to the calcium level. Can they have medicated chick grower mixed with crack corn?
For a "maintenance" ration (which means you're not currently breeding them) use 9% protein feed, made by mixing about 1 part 16% layer feed with 7 parts scratch grains. Make sure to provide grit when feeding whole grains.
Whether or not layer feed is hard on rooster's kidneys is commonly disputed on this site. I personally have no problems. A simple option is to feed all flock members a flock raiser feed (20% protein), and supply oyster shell for the layers, rather than keeping everyone separate. The roosters will not eat the oyster shell as long as they don't need it. Supplement the high protein feed with scratch grains if you're unable to free-range.
If you use 20% chick feed, make sure to get unmedicated for adults. That is for protecting chicks from coccidiosis as they gain immunity, which adult birds don't need.