At double stock they don't hurt the pastures (you're still running 1/2-1 acre per pair here if double stocked).  You deliver as much TMR to them as they need to keep both the cows and the pastures in good condition.  The cows gladly come to eat, they don't need to be locked up.
Actually, in late May and early June they often don't need any TMR because there is enough grass they won't eat it.