RMCA Resources

Mouse FAQ

The goal of the mouse FAQ is to educate the general public about the proper care of domesticated pet mice. This FAQ is in no way meant to supersede or replace veterinary advice. The text of this FAQ may be reproduced and distributed as long as nothing is altered, edited, or removed. It must be distributed in its entirety and full credit given to the author, Theresa Lee.

For Heide This FAQ is dedicated with love to Heide Walsh.
You are missed.


Q: What kind of pets do mice make?
Mice are nocturnal and will spend most of the day sleeping. At dusk, dawn, and throughout the night, mice are very active. A healthy mouse is always on the go and will rarely sit still for more than a minute to eat, groom, or for a pet.

Upon their first interactions with humans, most mice will be quite cautious. This is quite understandable, as everything seems big and dangerous to them. With time and socialization, however, mice will learn that humans, though big, can be kind. Once they learn this, most mice will eagerly come to greet their humans.

When you first bring mice home, give them 2-3 days to get comfortable in their new surroundings. Once they are comfortable in their new home, get them comfortable with you. The easiest and quickest way to do this is by letting them run around in a loose sweatshirt, on your person. Do this for at least 10 minutes a day, and by the end of 3 weeks, most mice will be comfortable enough with you that they will immediately step onto your presented hand.

You and your mice are now ready to travel, explore, and have lots of fun together. Everything still seems big and dangerous to your mice, but they now trust you for their protection.


Q: Where do I get pet mice?
The mice referred to in this FAQ are specifically the species mus musculus; the terms "mice" and "mus musculus" can be used interchangeably in this FAQ. Wild mice are commonly referred to as "house mice." Wild mice may be trapped humanely and relocated, but wild mice will be unhappy living locked in a cage and, thus, do not make good pets.

As early as Roman times, wild mice have been selectively bred for coat color, temperament, and health. Over many, many generations of such breedings, these mice have become what we know as domesticated mice. Domesticated mice are more docile than their wild or hybrid counterparts (wild and domesticated mice can and will interbreed). Domesticated mice, commonly found in pet stores and laboratories, make good pets.

Pet stores will often further label domesticated mice as either "fancy" or "feeder." One may have a different coat and/or eye color from the other, but the differences stop there. Both "fancy" and "feeder" are equally deserving of loving homes. Many animal shelters are also now taking in domesticated mice. Please always check your local animal shelters first when looking for new pets. All domesticated mice are equally deserving of loving homes.

Q: Besides the obvious, are their differences between male and female mice?
Unlike with rats, there are no marked gender-related differences in size, fur texture, or personalities with mice. Male mice give off much more odor than female mice, but both female and male mice are equally deserving of loving homes. All domesticated mice are equally deserving of loving homes.

Q: How many mice should I get?
Inasmuch as humans are social creatures, mice are also social creatures. Do everything you can to ensure that your mice have same-sex mouse companionship. Female mice usually have an easy time getting along with other females, while male mice have a very difficult time getting along with any other male other than those introduced to them at a very young age (under ~5 weeks). As examples, I have had the following groups each live harmoniously together: a group of 32 girls, a father and his 8 sons, and a group of 11 boys born about the same time, from three different litters. I also have had many male mice who had to be housed by themselves. I have never had a female who could not learn to live with another female.


Q: How do I introduce mice?
To prevent the spread of infectious disease, a quarantine of at least 3 weeks should be followed before attempting to introduce mice from different places.

Introductions should always take place on neutral territory. A well-scrubbed cage can often serve as neutral territory, but a place where none of the mice have previously marked will make introductions even easier. Plastic storage bins, bathtubs, and tabletops can be used as temporary, neutral territory. Once the mice have passed the introduction period, they can all be moved from the temporary, neutral territory to their well-scrubbed, permanent cage.

The introduction period typically lasts between 1-3 days, so weekends are a good time to try introductions. During the introduction period, maintain a close eye on the mice. Force the mice to sleep together by providing only one obvious place to nest. Loud squeaking, chasing, and dominance grooming are normal during and even after the introduction period. As long as there are no wounds that draw blood and everyone sleeps together, the mice can live happily together. If wounds, blood, and/or depressed behavior (e.g., someone forced to regularly sleep outside the nest box) are observed, the mice will probably not be able to live happily together and should be separated.

Many male mice will not be able to live with a male mouse companion and may have to be housed by themselves. With lots of human companionship, however, these mice can still lead very full and happy lives.

Q: What kind of commitment do pet mice require?
Mice typically live between 1.5-2.5 years. For their lifespan, you will be committing to provide water, food, shelter, and lots of love. The quality and quantity of water, food, shelter, and love greatly affects the lifespan of your mice. With plenty of clean water, good food, space to play, and love, your mice will lead long and full lives. Mice will also require medical care. If you are new to mice, allow for at least three vet visits for each mouse.


Q: What do I feed my mice?
Water should be available at all times. Water bottles keep water contained and clean. Water dishes spill, get buried with litter and waste, and, thus, are not recommended. If a water bottle is filled with anything other than pure water, the bottle should be emptied and cleaned out on a daily basis to prevent unwanted growth.

Food should also be available at all times. Always keep at least one food bowl filled with a dry rat/mouse food. These dry rat/mouse foods are available in grain mix, pellet, or block form from pet stores or online. As the nutritional requirements of rats and mice are virtually identical, these foods are typically marketed for "rat/mouse." These foods are fortified for their specific nutritional needs.

A second food bowl may be used for occasional foods. The nutritional requirements of rats and mice are significantly different from that of birds, hamsters, rabbits, dogs, cats, humans, and other species. Foods fortified for the nutritional needs of other species may be occasionally given to mice, but, to ensure overall, complete and balanced nutrition, these fortified foods should not be given in large amounts; whole foods which are not fortified may be given in larger amounts. Wet foods may also be occasionally given to mice, but, for spoilage concerns, any uneaten wet food should be removed after 24 hours. Mice enjoy cookie and chip crumbs as occasional treats. A small 8 ounce yogurt container may be used to collect these crumbs for your mice.


Q: What kind of shelter do my mice need?
The shelter for your mice needs to be clean, spacious, warm, and secure.

Two common primary shelters used for mice are aquariums and wire cages. A 10 gallon aquarium makes a nice home for 1-3 mice. Aquariums are easier to clean and offer more security than wire cages, while wire cages offer more ventilation and climbing surfaces for mice than do aquariums.

Though favorite pee corners are common, both sexes will ultimately pee and poop everywhere, and boys will dribble (mark their territory with little trails of pee). At the latest, cage surfaces, toys, nest boxes, etc. should be cleaned or changed out when a layer of pee-poop-goo can be felt. Soap, hot water, and elbow grease are sufficient for routine cleaning.

Chronic exposure to ammonia levels greater than 25ppm will adversely affect the health of mice. 25ppm is near the threshold of the human nose. At the latest, litter should be changed before the smell of ammonia can be detected. Comparing equal volumes of 8 commonly used litters, scientists have found that corn cob minimizes ammonia levels most effectively. (Litters tested, from highest to lowest ammonia levels, are aspen shavings, pine shavings, reclaimed wood pulp bedding, virgin pulp loose bedding, hardwood chip bedding, recycled paper bedding, virgin cellulose pelleted bedding, and corn cob bedding.) Regardless of which litter is used, litter should be changed before the smell of ammonia can be detected. Chronic exposure to the aromatic hydrocarbons found in cedar shavings will adversely affect the health of mice. Because these same aromatics are also found in pine shavings, neither cedar or pine are recommended as litters for mice.

Mice are always appreciative of more space. Once the size of your primary shelter is fixed, you can significantly increase the amount of usable space for your mice by replacing open space with hiding and climbing space. Try toilet paper tubes, paperboard boxes, egg cartons, and socks scattered and strung throughout the cage. All these materials are light, breathable, and either disposable or washable. Always be aware of crushing and suffocation hazards, and always keep things as clean as possible for your mice.

Because of their very high surface area to body weight ratios and very poor temperature regulating capabilities, large fluctuations in temperatures will adversely affect the health of mice. Mice also cannot survive prolonged periods outside a 65-80°F temperature range. A thermometer placed near your mice shelter and heating and cooling devices can be used to ensure that your mice live in a near-constant temperature environment within the 65-80°F limits. Chronic exposure to lights brighter than about 325lux or sounds louder than about 85dB will also adversely affect the health of mice. Direct sunlight measures about 100,000lux; a 100W unshaded, incandescent bulb illuminates at about 1,500lux 1ft away, and at about 150lux 3ft away. Food blenders typically operate at 85-90dB.

Simply by their size, almost every other animal species poses a danger to mice. Many animal species such as rats, ferrets, and cats will, in addition, instinctually prey on mice. The shelter you choose for your mice should protect them from all other animals. Mice should only be housed with mice. Mice should never be introduced to any other animal species without constant adult human supervision. A fatal blow to a mouse can be delivered in the blink of an eye.


What kind of toys will my mice enjoy?
All mice should have access to a wheel. Most mice enjoy wheel running, some much more than others. Mice also enjoy anything that gives them an excuse to climb, burrow, chew, and shred. As mentioned previously, toilet paper tubes, paperboard boxes, egg cartons, and socks scattered and strung throughout the cage are great mouse cage accessories. Bird toy, designed for climbing and gnawing are also well suited for mice. Dish towels, rags, scrap cloth can be hung, loosely piled, and folded over to make climbing surfaces, hammocks, and hidey holes. Toilet paper can be torn into coarse strips and offered as bedding material; mice will shred to suit their tastes. Straw or wicker baskets can be used for housing and chewing. Sisal or hemp rope can be used for climbing and chewing. Chopsticks stuck through two panels of cardboard can be used for climbing and chewing.

When choosing cage accessories and toys, consider ease of cleaning; keep things as clean as possible for your mice. Choose light and breathable toys; be aware of crushing and suffocation hazards. Cotton balls should not be given to mice as the long, thin threads pose a tangling danger to toes and tails. Loose threads on cloths used in mouse cages should be trimmed for this reason as well. Mice, like all rodents, have a diastema in which they can store and move around chewed material; gnawing and chewing does not necessarily mean ingestion. Just as human babies will try to put just about anything into their mouths, mice will try to chew on just about anything you put in their cage. Choose cage, cage accessories, and toys made from materials which are non-reactive in the mouth (will not leech anything toxic/caustic, electrically live, etc.).

Q: How much time should I spend with my mice?
The more time, the better! At a minimum, however, you should spend a few minutes in the morning, and a few minutes in the evening with each of your mice. These few minutes should be spent performing a health check. Mice can become deathly ill, very quickly; this is why a health check should be performed twice a day, every day. A mouse's survival from illness depends heavily on early detection and prompt treatment.


Q: How can I tell if my mouse is ill?
Unwillingness to move, hunched posture, weight loss, and a coat which is not sleek and smooth are all very strong indications that your mouse is ill. Save for the occasional sharp squeak to voice displeasure, healthy mice do not chatter, talk, chirp, brux, or make any sounds which are audible. Body and appendages should be examined for wounds and abnormal masses. Eyes, nose, ears, and the rear end should be examined for inflammation and abnormal discharge.

If any of these conditions are found, your mouse is likely ill. Mice can become deathly ill, very quickly. If you suspect a mouse is ill, immediately take the mouse to see a vet. A mouse's survival from illness depends heavily on early detection and prompt treatment.

Q: My mouse is chattering. What's wrong?
Chattering in mice is a symptom of respiratory disease. Respiratory disease is the leading cause of premature death in mice. It can be caused by acute respiratory infection, chronic respiratory infection, and/or damaged lungs. If quarantine is strictly followed, acute infection most often involves mycoplasma pulmonis. If quarantine is not strictly followed, acute infection most often involves m. pulmonis and the Sendai virus. These two pathogens act synergistically to produce severe respiratory disease. Acute infection most often involves at least the bacterium, m. pulmonis. For this reason, immediately treat acute infection with at least antibiotics such as tetracycline or enrofloxacin and, if Sendai infection is also suspected, antivirals such as ribavirin (Larson et. al., 1976). With prompt treatment, acute respiratory infection typically clears within 2-3 weeks.

If, after several antibiotics, chattering continues, your mouse likely suffers from chronic infection and/or damaged lungs. Chronic infection and/or damaged lungs most often result from acute infections which were left unchecked or treated too late. Chronic exposure to high levels of ammonia can exacerbate chronic infection and also damages lungs. Mice living with chronic infection and/or damaged lungs will be prone to respiratory flare-ups which should be kept in check with antibiotics, anti-inflammatories, and/or bronchodialtors.

Q: My mouse is scratching excessively. What's wrong?
Excessive scratching is a symptom of external parasitic infection. Species-specific mites or lice are the most common external parasites of mice. Mites or lice should be treated with antiparasitics such as ivermectin or pyrethrin. Ringworm is an uncommon zoonotic parasitic infection of mice and also results in excessive scratching. Ringworm should be treated with an antifungal such as griseofulvin. Excessive scratching often leads to scab formation and open wounds, and you may notice these before you notice excessive scratching. Open wounds associated with ringworm infection are often crusty. To prevent secondary bacterial infection, open wounds should always be cleaned at least once a day with an antiseptic such as sterile saline solution. Special attention should be paid to the ears. If ears are observed to be inflamed and/or scabby, the antiparasitic should also be applied topically directly to the ears, as mice will, literally, scratch their ears off. If self-mutilation is severe, glove rear feet with a small piece of masking tape folded over each foot to make dull, duck-like paddle feet. Gloved, paddle feet still allow for normal play, but will reduce the severity of self-mutilation.With prompt treatment, external parasitic infection typically clears within 2-3 weeks.

Q: My mouse has diarrhea. What's wrong?
Diarrhea is most often a symptom of antibiotic use or infection. Antibiotic use can disturb normal gut flora, allowing for overgrowth of certain bacteria (in mice, most notably citrobacter rodentium), and resulting in diarrhea. Diarrhea associated with antibiotic use should be treated with probiotics such as acidophilus. There are also several other bacterial, viral, and parasitic infections that can cause diarrhea. If antibiotic use can be ruled as a cause, differential tests such as fecal flotation or cultures will determine treatment. Electrolyte imbalance is a complication of diarrhea and should be treated with an electrolyte fluid supplement such as lactated ringers solution. Rectal prolapse and colitis are serious complications associated with diarrhea. Diarrhea should be treated promptly, before serious complication occurs.

Q: My mouse has a lump. What's wrong?
Lumps are usually either abscess or tumor. If under the age of about a year old, the lump is more likely an abscess, but a fine needle aspirate will be needed to differentiate between the two. This is a formidable task for many vets, and in many cases, the vet may chose to first treat the lump as an abscess, prescribing a systemic antibiotic. With a systemic antibiotic, most abscesses will shrink within a few days of treatment. If no shrinkage is observed, a fine needle aspirate will have to be done for a definitive diagnosis. At this point, if the lump is an abscess, it should be lanced and flushed. With prompt treatment, abscess typically resolves within 2-3 weeks.

If the lump is a tumor, it is most likely a mammary tumor. Like in rats, mammary tumors are not uncommon, however, unlike in rats, mammary tumors in mice most often turn malignant. Metastasis to the lung is most common. To prevent metastasis, treatment with chemotherapeutics such as tamoxifen (Matsuzawa and Yamamoto, 1981) or doxorubicin (Vaage et. al., 1992) should be started as soon as tumor is diagnosed. Without treatment, a tumor can become terminal within 2-3 weeks. With treatment, tumors typically go into remission, and at least 2-3 months can be easily added to the lifespan.

Q: My mouse has a swollen belly. What's wrong?
Swollen belly, excluding pregnancy, of course, is a symptom of internal cancer. By far, the two most common internal cancers of mice are leukemia and lymphoma. Like with mammary tumor, leukemia and lymphoma are only common in older mice, over a year old. Other common symptoms of leukemia and lymphoma are shallow breathing and swollen lymph nodes. With early treatment, combination chemotherapy such as doxorubicin-cyclophosphamide for leukemia (Avery and Roberts, 1977) and doxorubicin-interleukin 2 for lymphoma (Ho et. al., 1993) typically results in complete remission and easily adds 2-3 months to the lifespan of the mouse. Clinical signs of leukemia and lymphoma, however, generally present themselves at advanced stages of the disease. In particular, swollen belly due to ascitic fluid build-up is an extremely painful condition. Euthanization is strongly recommended if leukemia or lymphoma is diagnosed.

Q: My mouse no longer has quality of life. How should my mouse be euthanized?
The only humane way to euthanize a mouse is by inhaled gas anesthesia overdose. This can only be done at a vet's. There is no humane way to euthanize a mouse at home. Asphyxiation by carbon dioxide, by drowning, or in a plastic bag; freezing, cervical dislocation, or feeding to another animal are all incredibly cruel and inhumane. The only humane way to euthanize a mouse is by inhaled gas anesthesia overdose.

Q: Where can I get more information about mouse care and health?
For mouse parents, more information can be found online at the RMCA mouse forums. For veterinarians, more detailed information on mouse biology and veterinary technique can be found ad nauseam in the scientific literature. For example, dosages for common therapeutic drugs can be readily found in most veterinary formularies and are not explicitly referenced in this FAQ, whereas references for less commonly used therapeutics have been.