I use pine pellets (woody pet) for my rodents and the nursing moms with babies 2 weeks and under are put on pine shavings from Petsmart - it's very light and fluffy. If I don't put the newborns on shavings, I lose them. Was talking to someone who said that's because on pine pellets, they can't generate enough warmth and get too cold. Seems to make sense - they do fine after they are two weeks old on just pine pellets.