The grass clippings will mat down and go slimey smelly if they're not chopped up fine with lots of dry stuff like pine needles and/or wood chips. Or you can let the clippings dry first, then run them through a shredder to mix with other mulch.
I was afraid that it would rot, but I will try drying them out. If anything they can go in the composter or run. Just thought I would try it and see. It would be great not to have to lug out feed, pine shavings, and whatever else I have to buy at the feed store!
Just mow on a super hot day and they should dry pretty quick. The next day mow over it again in the morning (after dew dry). In the afternoon should be really short "hay". Works great. You can also gather dried leaves in the fall and bag them up for use in the winter. I deep bed and will use all the free stuff I can in addition to hay. They love the hay and are constantly scratching/stirring finding all the weed seeds. When cleaning coop it goes straight to the garden as mulch.
My Son dumps the grass clippings outside of the run and when they girls come out in the morning they have a wonderful time eating and scratching in it. The grass dries out as the girls spread it around and we are all happy.
My next door neighbor swears by Dried old leaves. And sometimes she uses Pine needles - My chickens love them too but mine are free ranged and hers are in pens. They do love to scratch but I would try to use your grass for composting and make a wormy smorgassboard! The chickees will love the wormees Too!