Dad raised cattle on grass, but would start 'graining' them to add marble to the meat before butchering time. I remember him using oats but since he's long gone I can't add more about the 'finishing' of the beef.
I do have an old book called 'The Farm Efficiency Manual' and it says that if you use corn to grain cattle you need to run pigs in with them as they will consume what the cattle didn't. Thus making it more 'efficient'.
Makes good sense to me!