Mice and rats: a history

Domestically raised mice and rats are popular pets these days; they are readily available, relatively inexpensive and easy to care for, and usually enjoy human handling.


All about mice and rats

These animals have been used extensively in research laboratories for many years. Consequently, their medical problems (many of which are inherited disorders resulting from intensive inbreeding) have been traditionally approached on a group basis rather than on an individual basis.

As a result, very little practical and useful information exists on the medical care and treatment of individual pet mice and rats. Furthermore, even less information is available to the pet owner on responsible home care of murine rodents and recognition of their potential medical problems.


The mouse, bearing the scientific name Mus musculus – interestingly, the Great Blue Whale’s scientific name is Balenoptera musculus – is thought to have originated in Asia. Its tremendous adaptability, long-time association with people and our dwellings, and unbelievably prolific breeding potential (one reference cites one million descendants from one breeding pair in 1 1/2 years) has allowed mice to enjoy a worldwide distribution. Mice are timid, social and territorial animals that spend a disproportionate amount of time in the wild pursuing an omnivorous (animal and plant material) diet. Feeding is most often carried out at night to escape predation. Laboratory and pet mice are not strictly nocturnal (night-active) but tend to exhibit alternating periods of activity and rest throughout the day and night.

In the wild, mice may exhibit aggression among themselves, though establishment of a social “pecking order” tends to reduce this potentially injurious behaviour. Individual males apparently dominate groups of mice using this social pecking order, and females with litters may fight to defend their nests.

Domestication and intensive breeding of mice have resulted in a tremendous genetic diversity of mouse populations. The Swiss Albino mouse has become one of the most popular strains for pets but many others are commonly seen.

  • Scientific name: Mus musculus

  • Life Span: 2-3 years

  • Potential Life Span: 4 years

  • Desirable environmental temperature range: 18-27°C/65-80°F (20-22°C/68-72°F optimum)

  • Desirable relative humidity range: 30-70%

  • Age at onset of puberty: 28-40 days

  • Estrous (heat) cycle length: 4-5 days

  • Estrous length (period during which female is receptive to male for copulation): 12 hours

  • Gestation (pregnancy) period: 19-21 days

  • Average litter size: 10-12 (1st litter usually smaller)

  • Weaning age: 21-28 days


The rat, bearing the scientific name Rattus norvegicus, apparently also originated in central Asia. Rats were domesticated in the 17th century and the process has continued to the present, resulting in many breeds that are docile which makes them great pets. Rats, like mice, have been used extensively in biomedical research. Most of the tremendous number of breeds and strains currently in existence have resulted from intensive inbreeding efforts by research laboratories over the years.

Wild rats are found in all kinds of habitats and nearly all land masses of the world, an enduring tribute to their adaptability and their long-time association with people. They tend to be omnivorous (feed on plant and animal material) but exhibit tremendous opportunism in their feeding habits when living in and around human dwellings. Wild rats tend to be nocturnal (night-active) animals but often use daylight hours to forage for food. Laboratory rats, like laboratory mice, on the other hand, are not strictly nocturnal. Mice and rats are both relatively short-lived animals, which can be disconcerting to owners of these pets.

Some, however, feel that having their children experience the relatively short period of companionship and subsequent death of pet mice and rats is a meaningful way to expose children to the “ups and downs” of life.

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