Down side to hay is that I have heard the chickens will eat long pieces that cause an impaction in the crop, so I personally wouldnt use. Why did you pick pine needles? Availability? I cant stand them! My neighbors tree drops them in my garden and they drive me nuts. The downside for their use is they are pretty acidic and not very good for absorbing moisture, and they get hung up on each other and the rake which makes raking out a pain.
Why did think you needed something other than dirt? I thought my girls would like some litter and found they hated it...they wouldnt go on it where it was deep, and scratched down to dirt where it was not!
I am considering adding in some Sweet PDZ for odor. It is $14 for a 40 lb bag of granuals at my local tack shop. Feed stores didnt have it, oddly enough...