[racinghamster]

I`m not familiar with aspen but I know it`s one of the `safer` wood-based options in the US. Although I would tend to try the paper based substrates or wait to see how the mice react to the aspen. You could add in some paper based bedding and not actually change things too much. Spot cleaning is a better way than tipping the whole lot out since like hamsters, mice like to retain some of their original scent. They do urinate more than hamsters and mice urine does smell more, so it`s just a matter of keeping on top of it really.

I used a product called `Cosi n Dri` made my Carefresh here in the UK and would highly recommend it for mice. Carefresh can be very dusty, but like everything else on the market, it`s all about finding one that isn`t going to cause the mice to sneeze or itch. Always air out any substrate a good week before using it in an open storage bin and give it a good shake around outside to release any fine cadis or particles. If you can hold a handful up to your nose and breathe it in without sneezing or smelling a strong scent, then it`s okay.