I use Swift premium horse bedding. If the pine is kiln dried, and dust free, then it should be okay for rats. Horse bedding generally is made to be easy on the repiratory system for horses, so it would be the same for mice and rats. If you get a bag, stick your face in it and take a whiff. It should smell like pine, but not REALLY LIKE pine, not like sticking your face in a pine tree. The more gentle the smell, the better the bedding for your animals.

I have had no repiratory problems with my rats since using Swift. But to my knowledge it's only available in VA unless you order an entire pallet.

Whatever you buy it should be labled as 'kiln dried' and 'dust free', 'screened' would be a bonus.