Pet mouse information

Domesticated mice kept as pets are usually referred to as fancy mice to distinguish them from their wild relatives. Fancy mice hail from the wild House mouse (Mus musculus) and have been selectively bred for numerous generations. Today, fancy mice are selectively bred both for tameness and appearance.
Fancy mice vary greatly in size with the largest specimens measuring up to 30 cm (12 in) from nose to tail and weighing up to 100 g (3.5 oz). The smallest ones will normally be no longer than 16–18 cm (6.3–7.1 in) from nose to the tip of the tail and only weigh about 25–40 g (0.88–1.4 oz).

Pet mouse taxonomy

Kingdom:      Animalia
Phylum:         Chordata
Class:            Mammalia
Order:           Rodentia
Family:          Muridae
Subfamily:    Murinae
Genus:           Mus
Species:         Mus musculus

Pet mouse care

Fancy mice are a popular pet for a number of reasons, including their fairly small size, cleanliness, amiability towards humans, inquisitive and active nature, and comparatively small price tag.

Ideally get at least two fancy mice because they are highly social creatures and it is difficult for a human keeper to provide them with enough social interaction. Females usually cohabitate with each other better than males who will fight each other unless introduced to each other at a very young age. Another advantage with females is that their urine is less smelly than the strong, musky urine excreted by adult males. Do not house unneutered /unsprayed members of opposite sex together unless you’re a fancy rat breeder.

Mice should never be housed with rats, since the rats will most likely end up killing them. Since mice are so afraid of rats they should ideally not even be housed near each other even if given separate cages since it will be very stressful for the mice.

Provide your pet mouse with things to explore and play with, such as empty toilet rolls, since this will make life in captivity less boring. Many mice like running wheels and tall structures to climb, activities which give them something to do and decrease the risk of obesity.

Training your mouse to like interacting with humans from an early age is recommended, since this will make it easier to take the mouse out of its cage and let it spend time outside on a regular basis, e.g. on your shoulder or in your lap. Don’t be surprised if your pet mouse urinate or defecate on you while first being handled, since this is a common behaviour, especially in new situations that make the mouse nervous.   

Fancy mice very rarely bite humans if properly socialized, but they may bite as a last resort if something hurts or really scares or them in a situation where it is impossible for them to escape.  

Pet mouse feeding

Wild house mice are known to feed on seeds, nuts, fruits and other similar types of food and have lived near human settlements, grain storages and fields for thousands of years. The species is believed to have originated in northern India and then gradually spread throughout the Mediterranean Basin about 8,000 BC. Due to its close association with agrarian human settlements above a certain size, it probably had to wait until 1,000 BC before it could spread to the rest of Europe.

Taking this into account, it is best to keep your fancy mice on a chiefly vegetarian diet consisting of various grains, oat, rice, and seeds plus fruits and vegetables. Serve it occasional treats in the form of protein rich, such as egg whites, but only sparingly in and small amounts. Not removing the egg shell will provide your mice with valuable calcium. There are also commercially available dry foods specially designed to meet the nutritional needs to fancy mice. Check the label though, because some of them have just been designed to be cheap to make – not to be good for mice. Your mice might very well survive on them, at least for a while, but it won’t thrive and the risk of future health problems will increase.

Fancy mice should always have access to wood and similar items to keep their teeth trimmed. Mice teeth grow continuously and must be gnawed down on a regular basis.

Fancy mice should always have access to fresh water, but will probably not drink much if you serve them fruits and vegetables as well.  

Coprophagy
Just like many other rodents, fancy mice eat their own faeces to obtain enough nutrients. This is a perfectly natural (and necessary!) behaviour and not something you should try to discourage your mouse from doing.  

Pet mouse breeding

If an adult male and female fancy mouse are placed together, they will normally produce a new litter every three weeks or so. Mice have a very rapid reproductive rate and the offspring, called pups, are born just 18-21 days after mating. A litter normally contains 4-12 young, but litters comprised of up to 20 pups have been reported. If the litter contains any stillborn or very weak pups, the female may eat them. Females come into heat roughly every fifth day and can get pregnant very soon after giving birth.

Mice pups are blind, deaf and furless when they’re born but hair will begin to appear after just 2-4 days. The ears open after 3-5 days, while the eyes remain shut until the pups are two weeks old.

Mice pups are usually ready to breed at an age of just 4-5 weeks, but females should not be allowed to get pregnant before they’re 12 weeks old or after they’ve reached an age of 8 months, since such pregnancies are very risky for both the female and the resulting offspring.

Pet mouse health

• Mice seem to become extra susceptible to cold viruses and flu-like diseases when exposed to drafts. They are not very good at regulating their body temperature and should be sheltered from both drafts and extreme temperatures. 
• Keeping your fancy mouse on an unhealthy diet and not providing it with enough opportunity to exercise can make it obese. Obesity is associated with a long row of health problems, such as diabetes, arthritis and cardiovascular disorders.
• As mentioned above, pet mice should always be provided with suitable items to chew to keep their teeth trimmed.
• You don’t have to bath or shower healthy mice since they groom themselves very carefully.
• Mice can become infested with various external and internal parasites, such as mites and ticks. Before using any remedy, check that it’s safe to use on mice. Don’t forget to sanitize the environment and check all other pets for parasites.  
• If your pet mouse develops diarrhoea, make sure it drinks enough fluids because these small creatures are susceptible to dehydration. Let any changes in diet be slow and gradual to avoid digestive problems  
• Older mice often develop tumours. In old females, breast cancer is especially common.

Pet mouse facts

Pet mouse facts # 1
The first known written reference to pet mice is found in the Erya, the oldest still existing Chinese dictionary, and dates back to 1100 B.C. In Europe, fancy mice did not become popular until the early 1600s when some pet mice from Japan were imported.   

Pet mouse facts # 2
Never pick a mouse up by the tail since this is very uncomfortable for the mouse and can cause injury.

Pet mouse facts # 3
Pet shops often sell both fancy mice and feeder mice. These are the same type of mouse sold under different labels. Feeder mice are used to feed predatory pets like snakes and fish, but can just as well be kept as pets. (Mice sold as feeder mice may however be in worse condition since the breeder does not expect them to stay alive for very long. They may for instance be kept on a less than optimal diet.) 

Pet mouse facts # 4
Fancy mice come in a wide range of colours, shades and patterns, including black, white, cream, champagne, fawn, cinnamon, chocolate, red, blue, dove, lilac, silver, silver agouti, and golden agouti.   

Pet mouse facts # 5
The first national mouse club in Europe was formed in 1895 by Walter Maxey. He named his club the National Mouse Club and arranged its first official show in Lincoln that year. Today, mouse clubs can be found world wide. During the shows, the mice are judged on both appearance and behaviour.

Pet mouse lifespan

You can expect your fancy mouse to live for 1.5-2.5 years, depending on its genetic predisposition, but improper care and diet can naturally shorten its lifespan drastically. Its wild ancestor the House mouse has an average life span of less than a year since it is exposed to hash environments and is a popular prey animal among predators. In protected environments, the House mouse can however reach an age of 2-3 years.  

The Methuselah Mouse Prize is a competition to breed or engineer long-lived laboratory mice. When I’m writing this article, the current record holder is a mouse that lived for 1819 days; almost 5 years. Another record holder was kept in a stimulating environment but did not receive any genetic, pharmacological or dietary treatment. Despite this lack of treatment, it lived for over 4 years (1551 days). In 2006, the award was raised to 4 million USD.