It's also easier to store than a bale of alfalfa. Sometimes in the summer, we get a bale and the rabbits and chickens split it. We just leave the bale outside, as it never rains in the summer here. In the winter, we have to jam it next to the straw bale in the shed and then do battle with the mice who think it is just the best thing ever. Like a gourmet feast we brought in just for them. 

I keep my hay outside and covered to protect it from any dew which can cause issues as well. Keep it up on a pallet so moisture cant get to it from the ground. NO matter where you keep it... On concrete or on dirt... Id even put it on blocks of wood in the feed room.