I was very nervous, as I have heard that hay causes impacted crops (many times heard that here on BYC). But I also read so many people had used hay without a problem, and that the chickens really like it. So I got a bale of alfalfa, and I have been putting a small flake in the run everyday. They really like digging through it for the leaves (they leave the stems), it smells great and keeps them busy. I make sure they always have plenty of grit to digest it. It's hard to keep them in greens this time of year!