Commercially prepared complete diets and balanced pellets for rodents or hamsters are acceptable for mice. Seed mixes are available, however, many times the mice will ignore the pellets in the mixture or eat only certain types of seeds in the mixture. This can result in dietary deficiencies even though a balanced diet "is fed," therefore the pelleted diets are recommended. The diet can be supplemented, in small amounts, with fresh fruits and vegetables, especially the cruciferous varieties like carrots, cauliflower, broccoli, and apples.
Rats have similar dietary requirements to those of mice; however, rats require higher fiber and lower fat, so limit those high-fat foods like nuts and sunflower seeds. Rats do well on block type diets which also provide them with gnawing exercise. This type of diet also eliminates the possibility of the rats eating only a preferential selection of seeds. Rats crave sweets, so resist the temptation of feeding anything sweet. What he/she never gets will not be missed.