Good point! I always forget that alfalfa is a legume.
I typically sprout some alfalfa seeds for them in the winter time, but haven't conditioned my (rock) dirt sufficiently yet for alfalfa to grow well here. It's on the list though. Until then, I'll probably be picking up a few bales of alfalfa for them to eat and play with. If those bales are anything like the wheat and barley straw bales I bought earlier in the year, I wind up with some sprouting on my property is a bonus.
Since my chickens decided to eat all the kale I'd grown for them in one fell swoop, I've started sprouting seeds early this year, starting with sunflower seeds, wheat grass, oats, and a mixture of clover + alfalfa + radish. I've also started sprouting some new kale and Swiss Chard indoors where they can't get to them. If I can get the aquaponics set up soon enough I'll transplant into that, but otherwise I'll transplant them into my raised beds AFTER adding bird mesh around my garden.