Caring for Mice and Rats

To many people the thought of keeping a mouse or a rat as a pet is amusing, and sometimes slightly revolting! The truth is the exact opposite – these rodents make excellent pets for all ages if they are cared for properly. They seldom bite when raised as pets and are handled with care. These timid and social pets are fun to watch performing their natural behaviors of burrowing, searching for food, and playing. Unlike their wild counterparts that are typically nocturnal, pet rats and mice have periods of activity both day and night. Rats and mice are inexpensive, easy to care for, and responsive to handling. It is true that mice can have a strong odour (not found in rats), but both animals are fastidiously clean – a far cry from the popular belief.

Feeding mice and rats

As with any pet, good quality food and clean, fresh water must be provided at all times. In the wild, these animals are omnivorous – they feed on leaves, seeds, roots, fruits and insects. Pelleted rodent rations are recommended for feeding in captivity, which are processed as dry blocks or pellets. These are not always easy to locate, but you should ask your local petshop to get them in for you. Seed diets are also formulated for mice and rats, but these diets should only supplement the basic rodent pellet as a treat item. Rodents prefer sunflower-based diets to pellets, but these seeds are low in calcium and high in fat and cholesterol. When fed exclusively, seed diets can lead to obesity and nutritional deficiencies.

Your pet’s appetite should be monitored closely. Many factors affect the rodent’s food intake, including the ambient temperature, humidity, food quality, breeding status, as well as the pet’s health status. On average, an adult mouse will consume about 15 gm of feed and 15 ml of water per 100 gm body weight daily. Comparatively, an adult rat will consume approximately 5 gm of feed and 10 ml of water per 100 gm body weight daily. Rats and mice typically eat at night.

Water should be provided in water bottles equipped with sipper tubes. The sipper tube keeps the water free from contamination. The tubes must be positioned low enough to allow the pet easy access. Inadequate water consumption leads to dehydration, lower body weight, infertility and death. These rodents drink only a fraction of the total bottle volume, but the bottle should be emptied, cleaned and refilled with fresh water daily.

Handling and Restraint of Mice and Rats

Pet rodents become tame and seldom bite when properly restrained and accustomed to handling. Be careful, however, when approaching a nervous or frightened pet. Also, it is best not to disturb a sleeping animal because most are usually quite cranky when awakened. Some rats can be very territorial of their cage, and these should be coaxed out of the cage before being handled. Mice housed individually may be more aggressive and apprehensive than those housed in groups. Most pet mice and rats enjoy being handled when away from their cage.

Rats and mice can be easily picked up by scooping them into a can or cupped hands. They can then be moved out of their territory to a neutral area. Mice can also be lifted by grasping the base of the tail. Rats can be picked up this way, but be careful not to injure them due to their larger size. For any rodent, never pull on the tip of the tail because the skin can easily tear and become stripped from the tail.

A mouse can be further restrained by placing it in a rough or wire surface and grasping the scruff of the neck using a thumb and forefinger. The rest of the body can then be restrained by trapping the tail between the palm and little finger of the same hand. This position allows for close examination and treatment.

Rats can be restrained by grasping over the back and rib cage, while restraining the head with a thumb and forefinger positioned on either side of the neck. To initially pick up a rat, it may be necessary to grasp the tail base as suggested above. Rats do not respond well to scruffing by the nape as described for the mouse, but it may be necessary in some cases.

Housing

Several types of cages are available which are suitable for housing small rodents. Many of these units come equipped with cage “furniture”such as exercise wheels, tunnels and nest boxes. These accessories contribute to the pet’s psychological well being. Cages should be constructed with rounded corners to discourage chewing. Rodents readily chew through wood and thin plastic. Recommended caging materials are wire, stainless steel, durable plastic and glass. Glass and plastic enclosures restrict ventilation and may lead to temperature and humidity problems. These materials are acceptable when at least one side of the enclosure is open for air circulation.

These pets thrive in solid bottom cages with deep bedding and ample nesting material. Bedding must be clean, non-toxic, absorbent and relatively dust free. Shredded paper is an ideal bedding. Wood shavings can be used, but they must be free of mould, mildew or other contamination. Cedar chips or chlorophyll scented shavings should be avoided because of association with respiratory and liver disease. At least one inch of bedding should be provided to allow for normal burrowing behavior. Shredded tissue paper makes an excellent nesting material.

Pet rats and mice can be housed singly or in groups. These rodents are colony oriented by nature. However, occasionally an overly aggressive mouse or rat may have to be caged individually. Territorial disputes also develop when the cages are overcrowded or when they lack food or water. Group cages should be provided with multiple food and water sources.

As a rule of thumb, the cage and accessories should be thoroughly cleaned at least once weekly. An exception to this schedule is when newborn babies are present, then wait until they are at least 10 days old. Other factors that may require increased frequency of cleaning are the number of animals in the cage, the type of bedding material provided, and the cage design and size. Cages should be disinfected with hot water and non-toxic disinfectant or detergent, then thoroughly rinsed. Water bottles and food dishes should be cleaned and disinfected daily.

Breeding Mice and Rats

Sex determination is the first step to breeding success. Fortunately, mice and rats are fairly easy to sex. Neonatal male rodents can be distinguished from females by a greater anogenital distance. Males have a one and a half to two times greater distance between the anal and urogenital openings. Sexually mature male rodents also exhibit a prominent scrotum. Females can be identified by their prominent bilateral rows of nipples.

Sexually mature mice and rats need to be properly paired to avoid fighting and permit successful mating. Adult male mice often fight when caged together, especially in the presence of females. Therefore, a single male mouse should be housed with one or more mature females. Rats, on the other hand, usually can be caged in mixed groups of males and females without aggression.

Female mice become sexually mature at about 50 days of age. They have an oestrous (“heat”) cycle of about every 4 to 5 days throughout the year, unless they are bred. Female mice are usually receptive to males for about 12 hours of this cycle, typically at night. They also have a fertile postpartum oestrus, which means that they can be bred within 24 hours after giving birth.

Gestation in mice lasts approximately three weeks, but can be up to ten days longer if the pregnant female is also nursing a litter. Litter size averages 10 to 12 young. Small litter size is common with a female’s first litter or older females. New litters should not be disturbed for the first few days to minimize injury or abandonment by the mother. Baby mice are weaned at about three weeks of age.

Female rats become sexually mature at about 65 days of age (although some rats can get pregnant at 35 days, so the sexes should be separated at 5 weeks to prevent early pregnancy). They have an oestrous cycle of about every 4 to 5 days throughout the year. Breeding usually occurs at night during a 12 hour period of receptiveness to the male. They also have a fertile postpartum oestrus, and can be bred within 48 hours after giving birth. However, unlike mice, this usually does not occur because the male should be removed from the cage prior to the female giving birth to avoid injury to the pups by the male.

Pregnancy lasts about three weeks in rats as well. Litter size averages 6 to 12, but smaller litters are common as described for mice. The female and her litter should not be disturbed for the first few days after birth, because a stressed female rat may injure or destroy her pups. Rats are weaned at about three weeks of age. The female will resume her normal estrous cycle within 2 to 5 days after the young are weaned.