Good-quality food and fresh, clean water must be readily available at all times. Laboratory rodent chows (milled pellets or blocks) are preferred. These foods are readily available from feed stores, pet shops, and suppliers or users of such commercial diets. Kibble-type kitten chows can be substituted. The rodent diets containing seeds and nuts are not recommended because they contain too many fats and oils, provide inadequate protein levels, and are not necessarily balanced.
Obesity is a common problem with pet rodents (especially rats). Consequently, oil-rich and high-fat foods must be avoided. Healthy maintenance of small pet rodents depends upon their receiving foods with relatively high protein levels 16% or more). Seed/nut-based diets generally fail to meet this requirement. Table scraps and alternative foods can be offered pet mice and rats, but these should be limited to healthful items (whole-wheat bread, non-fat yogurt, fresh fruits and vegetables, lean protein sources such as tuna, chicken, etc) and should not exceed 15% of what the pet consumes daily. If the above feeding recommendations are followed, malnutrition and related problems are very unlikely among pet rodents.
vitamin/mineral preparations and salt blocks (licks) are generally unnecessary. The food can be "dispensed" from a specially designed wire or mesh cage top that provides a generous depression into which the dry food is supplied and through which the food can be eaten by the rodent(s). This food-delivery system obviously depends upon the animals' ability to easily reach the food by standing on their hind legs. This type of arrangement is, therefore, not recommended when there are juvenile rodents within the enclosure preparing to wean.
This food-delivery system is used most often in laboratory situations. It has 2 major advantages. One is that there is much less wasted and discarded food. The other is that there is little opportunity for fecal (stool) and urine contamination of food. Metal "hoppers" can be used for dispensing food or it can simply be placed in heavy ceramic crocks (preferred because they cannot be easily tipped over) or similar containers.
This is most easily made available and kept free from contamination by providing it in water bottles equipped with "sipper" tubes. The tubes can become clogged with food debris, so they must be checked daily. The dispensing end of the tube must be accessible to the smallest rodent within the enclosure. Before juveniles are fully weaned, they begin drinking water and eating pelleted foods, so these essentials must be accessible to them at this time. Many deaths involving very young rodents of this age are due to starvation and dehydration.
Food consumption varies with the quality of the food(s) offered, the age, health and breeding status of the individual, the environmental temperature, and the time of day. Both mice and rats tend to feed at night, though daytime feeding among both is quite common. Mice are voracious feeders and consume proportionately more food per day than rats. This is because of their smaller body size and relatively high metabolic rate. Rats tend to be more reserved in their feeding habits. In fact, rats show great caution and selectivity while eating and tend to avoid unfamiliar foods.