I am planning the same thing. You will need to plant at least 2 or 3 seasons of crops. Peas, mangel (beets), mustard, and any cole crops or greens make good forage for spring and fall. Buckwheat would make a good summer forage. Depending on your site and the weather, you could get a cold crop, a warm crop and a cold crop for them to graze on. If you have 3 yards, you might want to do a spring cover in one really early, middle and late. Then, you can graze them on whichever plot looks best. If one fails, you just plant it with your warm crop. In mid/late July, you can switch over to planting your cold season crops again. If you want to store some seed for winter feeding, plant one of the plots with feed corn and sunflowers. That's about the best you can do in zone 5. At least, you would give the best chance for successful forage crops. If you have a long summer, you might be able to overseed with rye or clover to give a little extra green to control erosion.