Picky Eaters

The "boys" (Jack and Sundance) are driving me crazy! They have been spoiled all winter long with alfalfa and now they refuse to eat anything else. We have over 7 acres of grass and brush and they won't eat anything.... (except plastic, trash, my seedlings and my birthday balloons) It seems every time I turn around, they have something in their mouths but it is never something they should be eating. Meanwhile, they bleat nonstop for food.  I don't want to starve them, but how do I get them off alfalfa for the summer? Any ideas here????