Hmm, when we were blessed with a couple of large dogs the main problem was maize in the shop-bought dog food, it gave them eczema.
The Vet suggested cooking up our own meat scraps and veg concoction, and to use rice as the bulking agent. Both dogs prospered well on it - glossy coats etc, and it turned out to be cheaper than buying the dog food, just needed that bit of extra time cooking the butcher’s left-overs.