My experiences have made me completely abandon the use of pine shavings in my brooder pens. A while back I was brooding a batch of bielfelder chicks in a small box with a paper table cloth on the floor, the chicks were doing great without any problems. I decided to move them to a larger pen, so I cleaned and prepped the pen and put a nice layer of pine shavings on the floor. When I put the chicks in the pen they immediately started scratching and picking through the nice new shavings, unfortunately what I apparently didn't know was that they were eating the shavings. Within 2 days I had chicks with pasty butt, and after a week I had no chicks. I always had concerns about the very small pieces of shavings, so I always tried to get the larger chips with less fines in them, but they always had a certain amount. I know you can screen them to get rid of the small stuff, but I figured, why screen them and have to throw half of them away. My solution was to just not put anything in the pen that could be harmful to the chicks. Since then, I use disposable banquet table cloths that are made of paper that's a little thicker than tissue paper and has a plastic backing. I usually leave that in there for about 2 weeks or until they have it shredded up pretty good. I use a shop vac to clean up a little bit in between. Once I remove what's left after a couple weeks I'll add dirt or sand and some DE,and even a little barn lime to keep the smell down and neutralize the soil. If they're not to crowded it usually stays pretty dry. I'll vacuum it out as needed when it gets to be more poop than soil. As long as it's dry they scratch and dust bathe till their little hearts are content. In the past I've had several cases of pasty butt and several losses, since I said no to pine shavings, I've had 1 and only 1 case of PB which cleared up after I cleaned it. I've only lost two chicks since then, and they were just not meant to be, they never made it out of the hatcher. How many chicks did I hatch, you ask. Almost 200!
So, to make a long story even longer, I believe that introducing the chicks to pine shavings after 2 weeks with the one batch was probably not a good idea, my bad. I know that many places and people recommend pine shavings, but my experience has me looking for alternatives. My suggestion to anyone using them would be to screen the chips so that there is nothing small enough for them to eat. Just my opinion and observations. I would be interested to hear of any other types of litter people have used with success.