"Burn out" is a term often used for calves that go off of feed due to too hot of a ration. It is usually due to the fact that the calves Rumen is shutting down. In your situation with light steers I would feed a 12% protein feed at the rate of 2.25% of their body weight split between two feedings. You did not say how long you had to feed them out, number of days. We start at basically the same weights and have 230 days to feed. An example of what I do is feed a 650 lb. calf 14 lbs. of grain per day and a block of good grass hay after each feeding. As the weight of the steer increases adjust the amount of the feed until you get closer to show date, then you may increase to 2.5% of body weight. Others will have different ideas, but this has worked well for us.
Example: 650 lb steer x .0225 = 14.625 lbs. feed per day or 7.5 lbs. per feeding
Get yourself a set of scales and weigh 1 scoop of feed to see how this breaks down, whatever you do, do not allow them to eat all they want at the start. It is like a long distance race you must pace your feed program for optimal results. Good Luck.