Mice are omnivorous, but their preferred foods are cereal, seeds and many stored foodstuffs. The mouse has a simple digestive tract. A heavy-lactating female may ingest her own body-weight of food and water in twenty-four hours. This places an enormous burden on the alimentary system.
Mice are usually fed on pelleted diets which are best offered in hoppers where the animals have to eat the pellets through the wires. Mice are particularly liable to pull half-eaten pellets through the wire and let them drop to the bottom of the cage while they go back for more.
If a home diet is preferred, the best combination of foods is rolled oats, plain biscuits, mixed bird seed, bread soaked in water or milk, hay, fresh vegetables and water. An adult mouse will need a teaspoon of rolled oats and a teaspoon of moistened bread a day. Fresh, clean, raw vegetables are excellent for mice. Dandelion leaves and flowers, carrots, peas and clover areal suitable. Hay makes an important part of the mouse’s diet.
Smell the hay before you use it. It should have a fresh, clean odor. (If it is musty, don’t use it.) Mice will tumble through it, make a mess of it and thoroughly enjoy having it in their cages. Mice also eat insects. They love grasshoppers, crickets and cockroaches.
Mice also need something hard to gnaw on. It helps to keep their teeth in shape. A piece of rib bone or a section of shank is ideal.
Mice should have fresh water available at all times. A simple water dispenser attached to the outside of the cage with a nipple protruding into the cage is ideal.
Commercial products available for feeding your pet can be classified as moist foods or dry foods.
Moist foods usually contain 75 per cent moisture, 25 per cent solids. They may be complete rations, providing all requirements for the cat, or incomplete rations requiring supplementation with meat. Always read the label to ensure your cat is receiving a properly balanced diet.
Dry foods are 10 per cent moisture and 90 per cent solids. They can be mixed with each other or with other foods to satisfy the owner’s preferences and the cat’s taste.
Supplementary meat, eggs, table scraps, gravy, and so on, may be used, but in small quantities that should not exceed 25 per cent of the total diet; otherwise you run the risk of upsetting the balance of nutrients in the commercial product.
Where a home preparation is preferred, additional calcium, iodine, vitamin A and possibly trace elements are desirable. A five-month-old kitten being fed meat could have calcium carbonate and a daily egg (at least, the yolk) and some milk, if tolerated, to improve its diet. Meat should be cooked or if the cat prefers it raw, deep frozen for at least fourteen days to prevent parasite transmission. Whole eggs should be cooked also, as uncooked egg white is indigestible and it does contain half the protein content.
Mice may be housed in shoe-box-sized cages of almost any hard-to-chew material or in cages in which the walls and floors are wire mesh. If you decide to build a cage keep it simple—complicated cages are hard to clean and hard to keep clean. Make the cage roomy. Mice are active and enjoy exercises—give them treadmills, trapezes, ladders and slippery dips. For the individual hobbyist the ideal cage is a disused aquarium, as mice cannot climb glass walls.
Mice should not be held for more than a few hours in numbers greater than thirty per cage, however big the cage, because they tend to congregate in large heaps and those at the bottom may suffocate.
You can buy a mouse cage ready-made in a pet shop—a cage with one end is suitable housing, enclosed space for nesting and sleeping. A small wooden box 12 X 6 X 22 centimeters is suitable.
The top of the box should have gaps for entry of about 2.5 centimeters at each end. Make this top easily removable for examination of the nest. There is no need to place any nesting material in the nesting box itself. Just place soft paper, cotton-wool or hemp in the bottom of the cage and the mice will build their own nest.
Various types of bedding may be used, such as sawdust, wood shavings, cellulose, peat moss, granulated clay, dried woodchips, paddy husks and sugar beets. Whatever the material, it is important that there is enough of it to absorb the urine of all the animals in the cage because mice do not tolerate wet bedding.
Mice should be kept at a temperature of 20-25°C. They are very sensitive to noise, especially noise in the high frequencies
Mice are provided by nature with a very convenient tail by which they maybe picked up. Even a very pregnant female comes to no harm if held by the tail. The tail, however, should be grasped at least halfway down.
To immobilize a mouse more securely, put it on a rough surface such as the top of the cage and grasp a generous fold of the skin on the scruff of, a secure but comfortable way to its neck between the finger and thumb. The tail may be held and kept in place by the little finger of the hand holding its stump. A mouse so held can be comfortable.
Mice being small animals have a high metabolic rate and they therefore produce a lot of heat quickly. During transport their density should be low. They are much more likely to suffer from heat associated with lack of ventilation than from cold.
Mice will gnaw through most cardboard containers within a few hours.
To differentiate the sexes of mice, lift the mouse by the nape of the neck and examine the genital region. If the mouse is male, a tiny penis will be visible. Mice breed readily all year round. Breeding is more successful if they are kept in groups, either a number of females and males or a group of pregnant females together. The usual maternal group is three females with their litters. The young will be raised by a single nurse but may suckle indiscriminately.
Each female may produce as many as eight or ten litters if she is given the opportunity, but after the first five litters her productivity falls. The average litter size is five to eight. A breeding lifetime of up to nine months is usually enough. The male too should be retired after not more than six months of breeding. The best time to stop is when the mice are getting obese and their fertility is falling off.
The female mouse is ready and willing to mate within a day after she has given birth. If this period passes without a mating it will be six weeks before her next litter could arrive, because she will not again be capable of mating until the young are weaned. If you wait until the young are twenty-eight or thirty days old before they are weaned, they will be better mice, and will live longer.
Caring for the Sick Mouse
A sick mouse needs special attention and it is best to isolate it from the others. A shoe box will provide a spacious, draught-free, clean environment.
Punch some holes in the top (but not the sides) for draught-free ventilation and provide some dry grass or shredded newspaper for bedding. Change the water daily and provide fresh food, particularly fresh vegetables and bird seed. Place the box in a warm room.
Although the young are born hairless with their eyes and ears closed, they are very active and vocal from the time they are born. If they are not active they are likely to be rejected by the mother. At twelve days of age the babies open their eyes; by then they are very active and are able to run around. They will eat any solid food they can reach. They will also learn to drink water from a bottle or drinking utensil.
Mice are sexually mature at three and a half to four weeks of age, although females can be wooed at any time from sixteen days onwards. The female comes into estrus about every four days and is receptive for twelve hours. The gestation period is seventeen to twenty-two days.
Mating by an infertile male will develop a pseudo-pregnancy which lasts nearly three weeks. A male laboratory mouse will successfully mate two or three females in one night, but may become infertile through exhaustion of sperm while still able to copulate. It is in these circumstances that pseudo-pregnancies are induced.
Poor nutrition, overcrowding, lack of hygiene, inadequate ventilation, violent handling and exposure to mice suffering from infectious diseases, particularly wild mice, will all favor an outbreak of disease in the colony. A wild mouse is probably the greatest risk to the mouse colony. The mouse house must therefore be absolutely proof against mice (and rats) getting in as well as getting out and should also be protected against insects and other pests. Pellet feeds are unlikely to contain dangerous organisms.