The abusive industrial feedlots are by far the most prevalent implementation of the corn-finished beef model, if we go by sheer numbers. And "free-range" does not equal grass-fed, since there is no standard for that (cf "free-range" chickens, which may only have access to a small patch of grass, but otherwise be subject to factory-type conditions). But in general, grass-fed cattle are not fed on a monoculture of Bermuda grass. Also, chickens and cattle are not exclusive. On a well-run farm, the chickens can follow the cows onto the pasture that the cows have vacated, feeding on larvae in the cow manure and spreading the manure while they're scratching.