Both my chickens and myself prefer it when I use grass clippings in the pens instead of straw. The chickens like to eat some of what I put in fresh right after cutting, and the smell of the stuff that is both damp and dried is SOOOO nice in the pens. The only part the girls don't like is that there are many less flies to catch in the pens when they have fresh grass clippings.
I rake up some fresh when possible and give it to them, but this summer it has been so hot and dry that most of the time it isn't really edible even right when it is cut. Then I just leave it until the next day to dry really well, rake up and haul it to the pens in a wagon that pulls behind the mower. They never eat the dry stuff, I just figured it was like free hay, just cut up a little smaller. They love digging through it and moving it all around. It doesn't seem to get moldy, I guess because it has been a pretty dry summer and they keep it turned up all the time.