Mouse

A mouse (plural mice) is a small mammal that belongs to one of numerous species of rodents. The best known mouse species is the common house mouse (Mus musculus). It is found in nearly all countries and, as the laboratory mouse, serves as an important model organism in biology, and is also a popular pet. The American white-footed mouse (Peromyscus leucopus) and the deer mouse ( Peromyscus maniculatus) also sometimes live in houses. These species of mice live commensally with humans.

Although mice may live up to two years in the lab, the average mouse in the wild lives only about 5 months, primarily due to heavy predation. Cats, wild dogs, foxes, birds of prey, snakes and even certain kinds of insects have been known to prey heavily upon mice. Nevertheless, due to its remarkable adaptability to almost any environment, and its ability to live commensally with humans, the mouse is regarded to be the third most successful mammalian species living on Earth today, after humans and the rat.

Mice can be harmful pests, damaging and eating crops and spreading diseases through their parasites and feces. In western North America, breathing dust that has come in contact with mouse feces has been linked to the deadly hantavirus. The original motivation for the domestication of cats is thought to have been for their predation of mice and their relatives, the rats.

Body and behaviour

Mice are small rodents, resembling diminutive rats. They usually have pointed snouts and small ears. The body is typically elongated with slender, usually hairless tails, but different types of mice show large variations. Body dimensions vary considerably by species, though some approximate values are available: total length 28-130 mm, mass 2.5 to >34g.

Mice will eat meat, the dead bodies of other mice, and have been observed to self-cannibalise their tails during starvation. Grasshopper mice are an exception to the rule, being the only fully carnivorous mice. Mice eat grains, fruits, and seeds for a regular diet, which is the main reason they damage crops. They are also known to eat their own feces. Mice are often portrayed to enjoy cheese and people sometimes use it as mousetrap bait, though mice actually do not like cheese due to its fatty texture. Instead, they like food that contains high sugar, although chocolate is toxic to them.

Mice in captivity are observed to brux and boggle as an expression of pleasure or satisfaction. This is characterised by a grinding of their front teeth to make a soft chattering noise known as bruxing. Rats are also known to brux. Boggling is often in sync with the mouse's bruxing behaviour in which the eyes enlarge or pulsate in and out of the socket very rapidly.

Mice are social animals, preferring to live in groups. Male rivalry can become harmful for the animals, especially when a group is confined to a small space. The natural habitats of the mouse are very diverse. Mice can be found in forests, savannahs, grasslands and rocky habitats. In Africa they tend to particularly like forest edge, derived savannah, and (as elsewhere) agricultural areas. Mice build nests for protection and warmth, but species differ in their preferences: M. minutoides nests in shallow burrows; M. caroli and M. cervicolor burrow; and M. shortridgei and M. pahari nest aboveground. Most species will construct nests of grass, fibers, and shredded material. Mice do hibernate.

Mice are generally considered to be timid creatures in terms of behaviour.

The mouse has dichromatic vision, lacking a photopigment that can detect red light. There are diseases known to be spread by mice and rats which include:

• Rickettsial pox a disease similar to chicken pox and is spread to people by mites that are usually found on mice.

• Rat bite fever is spread to people when they are bitten by an infected mouse, rat, or other rodent.

• Food poisoning (namely salmonellosis) is spread to people when food, food preparation surfaces or dishes are contaminated by saliva, urine or feces from a mouse.

• Mice can spread parasites to people such as trichinosis and tapeworms.

• Hantavirus is a respiratory disease that is carried by small rodents, especially deer mice. It is spread to people when they breathe in dust that contains the rodents infected saliva, urine or feces. Although uncommon, people can also get hantavirus if they are bitten by an infected mouse.

Taxonomy of the genus Mus

The term "mouse" in common usage is roughly equivalent to the taxonomic term Mus, while house mouse is equivalent to Mus musculus. In common language the term "mouse" often refers incorrectly to Mus musculus. However, there are 41 species of mice (in the genus Mus); see table below.

Genus Mus
Subgenus Pyromys	Subgenus Coelomys	Subgenus Mus		Subgenus Nannomys
Mus platythrix Mus saxicola Mus phillipsi Mus shortridgei Mus fernandoni	Mus mayori Mus pahari Mus crociduroides Mus vulcani Mus famulus	Mus caroli Mus cervicolor Mus cookii Mus cypriacus Mus booduga Mus terricolor	Mus musculus Mus spretus Mus macedonicus Mus spicilegus Mus fragilicauda Mus nitidulus	Mus callewaerti Mus setulosus Mus triton Mus bufo Mus tenellus	Mus haussa Mus mattheyi Mus indutus Mus setzeri Mus musculoides	Mus minutoides Mus orangiae Mus mahomet Mus sorella Mus kasaicus	Mus neavei Mus oubanguii Mus goundae Mus baoulei Mus ferox

Nutrition

Mice should be fed a commercial pelleted mouse or rodent diet and water ad lib. These diets are nutritionally complete and do not require supplementation. Food intake is approximately 15g/100g BW/day; water intake is approximately 15 ml/100g BW/day.

Reproduction

Breeding onset is at about 50 days of age in both females and males, although females may have their first estrus at 25-40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the estrous cycle is 4-5 days and estrus itself lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating is usually nocturnal and may be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating.

Female mice housed together tend to go into anestrus and do not cycle. If exposed to a male mouse or the pheromones of a male mouse, most of the females will go into estrus in about 72 hours. This synchronization of the estrous cycle is known as the Whitten effect. The exposure of a recently bred mouse to the pheromones of a strange male mouse may prevent implantation (or pseudopregnancy), a phenomenon known as the Bruce effect.

The average gestation period is 20 days. A fertile postpartum estrus occurs 14-24 hours following parturition, and simultaneous lactation and gestation prolongs gestation 3-10 days due to delayed implantation. The average litter size is 10-12 during optimum production, but is highly strain dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh 0.5-1.5 grams at birth, are hairless, and have closed eyelids and ears. Cannibalism is uncommon, but females should not be disturbed during parturition and for at least 2 days postpartum. Pups are weaned at 3 weeks of age; weaning weight is 10-12 grams. If the postpartum estrus is not utilized, the female resumes cycling 2-5 days postweaning.

Newborn male mice are distinguished from newborn females by noting the greater anogenital distance and larger genial papilla in the male. This is best accomplished by lifting the tails of litter mates and comparing perineums.

Laboratory mice

Mice are the most commonly utilized animal research model with hundreds of established inbred, outbred, and transgenic strains. In the United States, they are not covered under the Animal Welfare Act (AWA) (administered by the USDA, APHIS) as an animal. However, the Public Health Service Act (PHS) as administered by the National Institutes of Health (NIH) does cover their humane treatment.

Mice are common experimental animals in biology and psychology primarily because they are mammals, and thus share a high degree of homology with humans. The mouse genome has been sequenced, and virtually all mouse genes have human homologs. They can also be manipulated in ways that would be considered unethical to do with humans (note Animal Rights). Mice are a primary mammalian model organism, as are rats.

There are many additional benefits of mice in laboratory research. Mice are small, inexpensive, easily maintained, and can reproduce quickly. Several generations of mice can be observed in a relatively short period of time. Mice are generally very docile if raised from birth and given sufficient human contact. However, certain strains have been known to be quite temperamental.

A knockout mouse is a genetically engineered mouse that has had one or more of its genes made inoperable through a gene knockout.

History

Mice have been known to humans since antiquity. The Romans differentiated poorly between mice and rats, calling rats Mus Maximus (big mouse) and referring to mice as Mus Minimus (little mouse). In Spanish similar terms are in use: ratón for mouse and rata for rat.

Discoloration in mice was supposedly first noticed in China by 1100 BC, where a white mouse was discovered. However, there is sufficient evidence to believe that white mice were first noticed before that.

The word "mouse" and the word muscle are related. Muscle stems from musculus meaning small mouse - possibly because of a similarity in shape. The word "mouse" is a cognate of Sanskrit mus meaning 'thief,' which is also cognate with mys in Old Greek and mus in Latin.

Mice as food

Humans have eaten mice since prehistoric times. They are still eaten as a delicacy throughout eastern Zambia and northern Malawi, where they are an important source of protein. In most other countries, mice are no longer routinely consumed by humans.

A common use of mice is to feed many species of snakes, lizards, tarantulas, and birds of prey. Most US pet stores now carry mice for this purpose. Because they breed quickly, grow quickly, are easy to care for, and can be sold in a wide variety of sizes, this makes them suitable for consumption by animals of many different sizes. Mice also seem to be a desirable food item for a very large variety of carnivores. Common terms used to refer to different age/size mice are pinkies, fuzzies, hoppers, and adults. Pinkies are newborn mice that have not yet grown fur. Fuzzies have some fur but are generally not very mobile, hoppers have a full coat of hair and are fully mobile but are smaller than adult mice. These terms also refer to the various growth stages of rats (also see Fancy rat).

Mice as pets

Mice have gained popularity as pets. Many people buy mice as companion pets. Some common mouse care products are:

• Cage- Usually a hamster or gerbil cage, but special mouse cages are now available. You can also use a small aquarium (5 gallons for up to 3 mice, 10 gallons for 8 or so mice) with a mesh top, so there is no risk of them escaping. However, this is not recommended, as the lack of proper ventilation can cause respiratory complications in mice.
• Food- Special pelleted and seed-based food is available. Mice can generally eat most rodent food (for rats, mice, hamsters, gerbils, etc)
• Bedding- Usually hardwoods, such as aspen, though shredded, uninked paper or recycled virgin wood pulp can also be used. Cedar or pine should not be used because they contain harmful liquids that can damage any rodent's respiratory system. Corn cob bedding should also not be used because it promotes Aspergillis fungus and can grow mold once it gets wet. It also is quite rough on their feet. Whatever the bedding material, there should be at least 2 inches for digging and burrowing purposes.

Some benefits of having mice as pets are

• Minimal shedding and allergens
• Entertaining and affectionate
• Inexpensive
• Clean (contrary to popular belief)
• Socially self-sufficient (when in a group of other mice)
• Significantly less likely to bite than other rodent pets
• Mice are quite intelligent given their size

There are, however, some disadvantages to having pet mice

• Small and quite fragile (not as easy to handle as a dog or a cat)
• Mice defecate and urinate frequently
• Noticeable pungent odour
• Nocturnal
• Frequent eye infections under stress
• Easily subject to disease when without optimal care
• Frequent reproduction
• Short lifespan
• Prone to many other diseases