When I first got chickens I used HAY...I had to clean out my coop DAILY sometimes twice a day...the straw is nice at first, then it gets hard and brittle and pokes you....if it poked me I thought it can poke my babies especially if they are laying, the poop would also make the Hay mat up bad, and talk about flies!!!! BAD
I switched to shavings and I love it!!!! soft, clean, no flies, and I switch out my shavings about once every 6mos...I do go in and sift it like you would cat litter, and once I trash the poop, I add just alittle more fresh shavings, no flies either!!!! and the flock loves it...
Another word on Hay, I read in several books, and on the net...that hay is HOLLOW, so thus it can make wonderful houses for lice, mites and other parasites...AND HAY IS "HOT" in summer.