In nature the rat is an omnivorous animal and is able to use and transform almost any type of organic material that it finds (Fig. 1). Specifically formulated food pellets based on cereal flours (corn, barley, wheat, wheat germ), legumes (soya beans and alfalfa), meat, fish and whey powder are commercially available. The percentage composition is about 12% of moisture, 17-20% proteins, 4-5% fats and 3-5% raw fibre, although there is enormous variability from one type of feed to another. These pellets are usually large (1 cm in diameter and 2 cm long) and of a pale brown colour that can vary depending on the raw materials included (Fig. 2).
Alternatively, rats can be fed a mixture of seeds (corn, oats, wheat, millet, barley and sunflower, being careful with the amount of the last, since sunflower seeds lack calcium and are rich in fats and cholesterol) and flaked food. Fresh food, for example lettuce, carrots, peppers, celery and fennel, is greatly appreciated and also provides vitamins, but legumes and cooked cereals (preferably not dressed), pasta (raw or cooked), bread and biscuits are also welcomed, although, particularly for the last three types of food, it is important not to give too much. Occasionally (once or twice a week) the rat can be given very small amounts of light, dry kibbles for dogs or even smaller amounts of dried fruit. Chocolate should not be given.
Food pellets for rats are usually supplied ad libitum; in general, the average food consumption is about 5-10 grams every 100 grams of body weight which, in practical terms, means about 15-30 grams of food each day.
Water should be supplied from a specific drinking bottle with a drip stopper or ball-bearing and must always be kept clean and fresh: the average consumption is 10-12 ml every 100 g of body weight, but water, too, is usually supplied ad libitum. Drinking water can also be provided in a bowl, but this is strongly discouraged because of the risk of overturning the bowl or the water being contaminated by faeces and urine.