We actually put old hay mixed with cow manure in the run for our girls to dig around in when we have to keep them penned up. We got the idea to do that while watching them free range. They're always rummaging through our large manure/hay/pine shaving compost pile, and actually help to break it down faster by constantly turning it over. We don't use an entire bale in their run though, only about a wheel barrow full, and I turn it daily if it gets wet or starts looking mucky. They love it! I'll rake it into a tall pile in the morning and they'll hop on it as soon as I let them out of the coop and start scratching it down. I do this with leaves as well and they break it all down to some very nice dirt. I think a whole bale would be too much. Once it's broken open, it really spreads out and
mats up, especially if wet, and they can't really scratch through the large mats. I've seen them try around our cow's hay feeder. I have to use a pitch fork for that. But when I turn that over, they dig into it with relish to get any bugs that may be under the wet hay. You could try just a few flakes at a time and
see how they do with it. Mine have become great little composters. In fact, my husband now has little piles of hay, pine shavings & manure in part of our yard that I'm converting to a garden next year, that the chickens have in various stages of composting. They absolutely love digging in the piles and we haven't seen any sign of respiratory issues. I do make sure to constantly turn whatever I
put in their run for them to play in / to keep them occupied, in order to keep it from getting stagnant. It only takes a minute or two and there are usually sprouts and grubs underneath that they eat. I've read on some of the BYC forums where people throw scratch onto their deep litter to keep it turned over and/or fresh. Same concept. I just have them break it down to dirt. Then I remove the dirt and start all over. They don't care what they're scratching, they just love to scratch. Our chickens are by far the most productive animals in our household.