We've found that feeding just corn isn't enough protein to get the fast gain needed for profit.  We mix in high protein pellets with the corn and give them all they want.  The ratio of pellets to corn decreases as the lambs get older.

The thing about lambs is you pay too much for the feeders IMO.  Plus, it takes a while to get them started on feed and I've never like mixing sheep of any age from different flocks.  Also, DO NOT let them run out of feed, or they will over eat when they have access to it again.  Over eating shots are a must (twice).