I breed both as well. For my little guys, it's much easier to give them the right sized mouse and get a feeding response than a rat pup that doesn't move much. Also for the mice I used a base layer of alfalfa pellets and top with pine shavings. The alfalfa really keeps the smell down. My rats, mice, and snakes are all in my bedroom so keeping smell down is important to me. For the rats I used a base of pine pellets and top with pine shavings. The alfalfa pellets are more expensive and not needed for the rats so I just use them for the mice. I change mouse and rat tubs every week and the mice don't smell any more than the rats do. I also don't have a problem with them cannibalizing. I have them in a mouse rack and keep one male per tub. The females all raise the babies in one big pile.