There is a sub-forum for showing cattle that may have some threads you would find helpful. I don't show cattle but I know that show rations can be very tightly guarded and be very complicated custom mixes. If you have a feed mill nearby you would be wise to go there and have a discussion. They very likely may have a recommendation and they almost for sure will be cheaper than bags of feed from a farm supply store.
There should be others with actual experience along shortly to give you better responses. Good luck!