Best beef is range fed with a 90-120 day grain finish. Leave off that grain finish and you will lose marbling and the meat will be lean, and will taste gamey to city pallets.
And grain finishing is seldom corn. I wish. Corn is the cheapest grain you could use. Cracked corn with be part of it - as filler - but you want a high protein finish - 20-22% feed - That's oats and barley. Feed that runs heavy to corn is 15%
I never ran the finisher. I finished em on oats, barley, and molasses, with a free choice molasses mineral tub... And a touch hot on the hay... An orchard mix with a little bit of clover and alfalfa... That'll get you a prime beef with a nice, marbled meat, and not a whiff of gaminess.