What weight are the steers, and what is the grain? There is a negative interaction between grains such as corn and forage digestion because of the starch in the grain. Even with this negative interaction, they will likely weigh more than calves that do not receive corn. The ration that you described, especially if you are feeding 7 lb of corn to a 550-lb steer, means that about half of the dry matter intake is grain, and calves will likely experience less of a negative interaction in this situation. If you wanted to supplement, consider a grain co-product such as wheat mids or corn gluten feed, distillers grains, or a pellet that has these products. These feeds do not have a negative interaction with forage digestion. Typically what we do is try to get as much gain on grass that we can without supplementation other than vitamins and minerals, then move them to a lot situation and feed mostly grains. Some data show that calves on grass fed distillers grains outperformed non-supplemented calves. The dried distillers grains were fed at 0.42 and 0.79 percent of their body weight. You would need some calcium when either feeding gluten or distillers grains. The economics boils down to increased performance, price of the feed, labor, and fuel costs.