If your rats or mice haven't eaten Pets at Home Rat & Mouse Muesli before, it's best to introduce it slowly over 10 days or so. The above is a guide only as an individual rat or mouse requirements may vary depending on size and environment. This muesli is perfect for weaned and adult rats and mice but not suitable for any animals other than those stated. Don't forget, your rats and mice always need a supply of fresh water. Treats such as fruit and veg can also be given occasionally. Rats and Mice require plenty of exercise and toys to keep them active and mentally stimulated, and special chews can also be provided to help keep their teeth from becoming over grown.