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Mice & Rats

Domestically raised mice and rats are very popular pets in the United States. They are readily available, relatively inexpensive and easy to care for, and usually enjoy human handling. 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.

Mice: The mouse, bearing the scientific name Mus musculus (interesting in light of the fact that 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 behavior. Individual males apparently dominate groups of mice using this social pecking order. 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 used in this capacity.

Mice Vital Statistics:

  • Scientific name: Mus musculus
  • Life Span: 2-3 years
  • Potential Life Span: 4 years
  • Desirable environmental temperature range: 65-80 F (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
  • Estrus 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

Rats: 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 and of excellent pet quality. 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 early 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.

Rats Vital Statistics:

  • Scientific name: Rattus norvegicus
  • Life Span: 3-4 years
  • Potential Life Span: 7 years
  • Desirable environmental temperature range: 65-80 F (68-72 F optimum)
  • Desirable relative humidity range: 30-70%
  • Age at onset of puberty: 50-60 days
  • Estrous (heat) cycle length: 4-5 days
  • Estrus length (period during which female is receptive to male for copulation): 12 hours
  • Gestation (pregnancy) period: 21-23 days
  • Average litter size: 6-12 (1st litter usually smaller)
  • Weaning age: 21 days

Human Allergies to Pet Mice and Rats: Human allergies to rodents are common. The signs can be serious, even life-threatening. This problem is most frequently reported among laboratory personnel, but individual pet mouse and rat owners are equally vulnerable. The offending allergens may be rodent skin dander and hair, or the proteins in aerosolized rodent urine. Signs among allergic people may include runny eyes and nose, sneezing, congestion, coughing, shortness of breath, and anaphylactic shock. Some people develop a rash and/or hives, especially in areas contacted by the claws or hair of a rodent. Allergy to a pet mouse or rat must be considered if someone in a household develops any of these signs. The medical doctor consulted about the problem must be made aware of the existence of a pet rodent within the home.