Pet Mice – A Mouse In The House Is Nice

Mice As Pets

Ron Hines DVM PhD

I have always been partial to mice. I know of no other pet that offers so much personality in so small a package.

When I first graduated from veterinary college, I had the choice of going to Vietnam as a soldier, or going to Bethesda, Maryland to care for 20,000 research mice. I chose the mice.

Mice are rodents; and there are many many species of mice found throughout the World. But the one this article is about is the common house mouse, Mus musculus. Scientists believe that house mice originated in Asia. The Chinese were known to be keeping them as pets as early at 1,100 BC. Slowly, the domesticated strains of this rodent became calmer, and lost their ability to live on their own. During that period, strains were developed for special colors, individual size, coat texture and particular temperaments and idiosyncrasies. (ref)

Domesticated mice became popular in England in the late 1800s and were called “Fancy mice” or “Hobby mice”, to distinguish them from their wild cousins that zipped along the kitchen floor. About this time too, scientists began to find these slower varieties convenient for experimentation.

Today, in the United States, pet shops sell most of them as “Feeder mice” – due to their tragic fate of ending up as the diet of various carnivorous lizards and snakes.

Do Mice Make Good Pets?

I think they make excellent pets. They are curious, gentle animals that are quite intelligent for their size. They make no loud noises, they cost very little to feed and house and they are a pleasure to observe and interact with.

They also have their limitations. Mice are, by nature, more timid than dogs and cats. They have only two speeds – on and off – and they do not live very long. Most mice live 740 to 1,000 days. Because they only weight 1-2 ounces (28-56 gm), they are very fragile. Mice tend to most active during the time you are probably sleep. When they escape from their cages, they can be hard to find. They cost practically nothing and are inexpensive to maintain.

What Strains Of Mice Are Commonly Available To Purchase?

The basic brown color of a mouse is called agouti. From that color, breeders have bred innumerable colors and color patterns. Some are: black, chocolate, white lilac, red, fawn, champagne, cinnamon, silver and dove. Mouse clubs call mice that are all one color “selfs”.  “Tans” are one sold color on top with a tan belly. Patterns are classified as even or broken.

Feeder Mice

The most readily available mice are the feeder mice sold at pet shops. These are randomly bred mice of no particular strain. They are inexpensive, but because no one really cares how long they live, they tend to be raised by suppliers in dirty, crowded conditions with inadequate nutrition. Still, given some love and TLC, it is amazing how nice they can become.

Fancy mice

Fancy mice are mice that are bred as pets and for show. If you live in the USA, purchase your mice from a member of  AFRMA  (American Fancy Rat And Mouse Association) or the  RMCA (Rat And Mouse Club Of America) . If you live in the UK, purchase them from a member of the  NMC  (National Mouse Club). Some of the fancy mice strains are very large. Feeder-type mice mature at about 30 grams, but fancy mice can weigh three times that amount.

Laboratory Mice

Many strains of mice, normally used for scientific research, make wonderful pets. My favorite are the BalbC mouse and the C57Black6. Individual mice of laboratory strains are only available to people with connections to scientific institutions. Most owe their origins to the colonies maintained at  Jackson Memorial Laboratories  They supply some really weird strains (transgenic mice) – like theC57B6 that glows in the dark which contain mouse, human and jellyfish DNA. The best thing about mice from these laboratory colonies is that they are free of all the diseases common in pet store mice. However I do not believe that they would sell to the general public.

Wild Mice

It is unwise to try to make pets of wild mice. They may start out docile when they are babies, but they mature to become spooky and fast and rarely calm down or become affectionate. They can also carry a number of serious diseases, includintg LCM, that can infect their human owners.

Are Mice Dirty?

Mice are , by nature, very clean. They spend much of their time grooming and washing themselves. They are careful to choose one corner of their cage to eliminate at and tend to gather up all the loose objects in their cage in one place.

When odor becomes a problem, it is because the cage is too small, the bedding is soiled or the atmosphere in the room is stagnant.

What Are Some Of The Negative Points About Mice As Pets?

Mice have very short lives. If seeing them age and pass on bothers you, you may want a pet that lives longer.

Mice do mouse things, not dog or cat things. So if you want a pet that fetches a ball, purrs and rubs up on you or one that protects your house, a mouse may not be for you.

Mice don’t do well loose in the house. They tend to disappear into the insides of sofas and TVs where they often chew the cords and do damage.

Mice sleep a lot when owners tent to be active. You can wake them up gently to interact with them, but they are not going to wake up and come to play when you call.

Mice are very fragile. If you step on your cat, it will complain and run off. But if you accidentally step on your mouse, that is the end of it.

Do Mice Make Good Pets For Children?

That depends on the maturity of your child. Some children are responsible enough to own a living pet when they are 9. Others never are. If there is any doubt in your mind, don’t get a mouse.

Mice are tiny, delicate creatures, children can easily injure them. If you do get mice or other rodents for your children, be present to supervise and instruct.

Are Mice Hypoallergenic?

No. if you are looking for a pet for an allergic child or adult, mice are not for you. They appear to be  responsible  for more inner-city allergies than dogs or cats. ( ref ) Reptiles, like turtles, seem to be less of a threat to allergic children. But remember, reptiles often carry salmonella bacteria.

How Long Do Mice Live?

Most mice have the potential to live about two years. Occasional mice will live over three years and some will die before their first birthday. Most authorities say 1.5-2 years. How long your mouse will live depends on a number of factors:

Some strains of mice just age faster than others. Among laboratory mice, strains like the NZB live less than a year, due to inherited genetic diseases, while others, like the C57 live 2.8 years.

The oldest known mouse – the 2004 Methuselah mouse – lived 1819 days. I talk about the dietary/caloric restriction that achieved this later in this article.

Many commercial mouse colonies that supply the pet trade harbor viruses  that shorten the lives of mice. Since pet shops purchase most of these mice as inexpensive feeder mice at the lowest possible price, these mice are often contaminated with a variety of non-viral diseases that also shorten their lives.

But how you care for your mice and what you feed them has a major influence on how long they are likely to live. A wildly know fact among aging (gerontologist) scientists is that restricting caloric intake, significantly  lengthens  the lives of mice. So do not let your mice get as chubby as the one at the top of this page.

Where Should I Get A Pet Mouse?

The best mice come from individual mouse breeders who are not breeding in volume to supply pet stores. In the What Kind Of Mice Are Available Out There? Section, I mentioned some organizations that will give your leads to local, conscientious, mouse breeders.

That said, most families obtain their mice at pet shops or their children bring them home from friends and schools. A few kind hearted soles rescue mice that were destined to end up as snake brunch. Occasionally, animal shelters end up with unwanted pet mice as well.

How Can I Pick Out A Healthy Mouse?

When you go to select mice, do not pick the largest or smallest ones in a litter. Look for the ones that are curious and come up to sniff your fingers.

Do not pick individuals that are scratchy, scruffy or have crusted, snotty or discolored noses or squinty eyes. Be sure their stools are well-formed pellets. Mice should be silent. If you hear wheezing or sneezing from the mice, they are not healthy. Do not believe the salesman if he says it is the dust in the litter that is causing this.

If any of the mice show these unhealthy signs, even the ones that appear normal are probably contaminated.

Do not let your child pick out the mouse. Pick out the ones that seem the healthiest and let your child pick from those.

Pick mice that are active – not the ones that are sitting calmly off to the side. Pick only mice that have clean, shiny coats, clean ears, bright open eyes, and normal tails. Do not pick mice that have soil and stain around their rear ends.

How Old A Mouse Should I Buy?

The best age to buy a mouse is when it is five weeks old. They can live independently , a week or so earlier but they will be hardier if they spend that last week with their mothers. I discourage purchasing mice over 9 weeks old. If they have not been handled and socialized individually by the store owners by then, they sometimes remain skittish and unsocial. If they sat around the pet store for 9 weeks, they have probably been exposed to a lot of extra diseases there as well. Mice are fully grown at 12-16 weeks.

How Many Mice Should I Get? Should I Get A Male Mouse Or A Female Mouse?

Because mice are social animals, two mice will be happier than a single mouse. Mice do not like to live alone. They get board, lonely and depressed. This leads to aggression and extra time sleeping. So plan on getting two mice.

When you buy the mice, buy two that are the same size. I suggest you purchase two girl mice. Female mice tend to be gentler and less aggressive and their urine smell is less intense. Female mice also tend to live slightly longer than male mice

Male mice have a stronger odor, and two mature males will often fight and injure each other. When this occurs, one male will eventually dominate the other and fighting may end. The males may accept each other if they were raised together from weanling size – but why risk that. If you are confronted with this situation, having the male mice neutered may help.

Fighting is worst when two older males from different litters are suddenly placed together as roommates.

Is It Hard To Tell A Boy Mouse From A Girl Mouse?

Do not trust inexperienced pet shop employees to correctly identify the sex of mice. Immature mice of both sexes look quite similar to untrained eyes.

Female mice have genital openings resembling – o whereas boys resemble

o .o. That is, there is more distance between the openings of boys and both openings in males are circular. You can pick them up by the bases of their tails to look.

When in doubt, compare several mice in a litter until the difference becomes clear to you.

In mice over 14 weeks of age, the differences are quite obvious. The scrotum and testicles of male mice at this age bulge out unmistakably. Even when a nervous male mouse sucks its testicles up into its abdomen – it’s wrinkled scrotum is still prominent. The younger the mice are, the more experience the salesperson needs in identifying their sex.

Beware of purchasing female mice over 6 weeks old because they are often already pregnant.

What Should I Feed My Pet Mouse?

House mice have adapted to survive on almost any food source likely to be found in the home. But if you want your mice to remain healthy, feed them a balanced rodent block or pellet. These blocks are formed of compressed animal and plant proteins and grain carbohydrates with added vitamins and minerals. Scientists worked out the exact nutritional needs of mice a long time ago.

I mentioned that I once maintained 20,000 mice and about half that number of rats for the National Institutes of Health. My favorite mouse diets at the time were Purina Mills,  Mazuri,  Harlan, and  Zigler Brothers  (ask for the 16-5 lower protein, lower fat, formula). If those companies are still in business when you read this and if their product formulas have changed is something I can not tell you.

If there is a problem with these diets, it is that they have more protein and fat in them than is optimal for non-breeding, pet mice. Ideally, I would feed pet mice a diet with approximately 15% crude protein, 2% crude fat and 6% fiber to obtain the  life-extending benefits  of caloric restriction. Not all these companies sell their diets in small enough packages for individual mouse owners. It is best if you keep larger containers frozen or in the refrigerator to prevent weevil infestation and nutrient loss.

I don’t  suggest that you give your mice commercial rodent seed mixes because the quality of these mixes varies from batch to batch. Generally, these grains and seeds are second quality – that is unfit for human consumption. These mixes can also be contaminated with everything from fungus toxins to rodent poison.

Mice cannot survive long without food. They are constant nibblers who should have their food available to them at all times.

It is fine to give your mice treats – as long as they do not make up more than 20% of their diet. Mice enjoy slices of garden vegetables, fruit and nuts. Keep your mice trim. Do not allow them to become pudgy – like the one in the photo above.

What About My Mouse’s Water Needs?

Mice need to have a water bottle available to them at all times. I prefer the ones that have a ball bearing in the sipper tube so the mice do not run the water out playfully. Crocks and dishes tend to fill up with bedding and poop. Change the water daily.

I Need Something To Gnaw On

The front teeth (incisors) of all rodents continue to grow throughout their lives. To keep these teeth from getting too long, the mouse needs something to gnaw on. I prefer a block of hard wood – such as hard rock maple or dense oak. A section of axe handle hickory also works well as does a piece of deer antler. Antler and bone supply the mice with added calcium as well.

What Kind Of Cage Should I Buy For My Mouse?

A twenty-gallon aquarium makes a nice cage for two or three mice. You will need a screen top to keep the mice from escaping. When mice are kept in an aquarium, steps must be taken to prevent them from overheating. You can purchase a temperature/humidity gauge designed for fish or reptiles. Be sure there is sufficient air circulation to keep the temperature from rising over 80F. Add some rodent condo shelves to give the mice different levels on which to hang out. Use dish washing soap and a sponge to clean it.

I recommend against wooden cages. Odor and contaminants penetrate wood. But if you do make one, do not use green or pressure-treated lumber to construct it.

Singly kept mice are more prone to escape than a pair. They will only do it a few time before decide life in the cage is better than the freedom of the house. Mice are quite territorial and soon know that the aquarium is their special space.

What Kind Of Bedding (litter) Should I Purchase?

My favorite bedding for mice are commercial prepared , sanitized ground corn cobs. My next best favorite is ordinary newspaper or paper that has been passed through a document shredder. Most inks these days are non-toxic soya based.

Cedar chips have a pleasant, aromatic odor that masks urine smell. But some feel that cedar, aspen and other strong-aroma bedding are not good for the pet’s health. Most plants contain these natural chemicals to make them distasteful or poisonous to insects.

How Often Should I Change The Bedding?

You should change the bedding of your mouse or mice whenever you sniff the smell of ammonia. Ammonia irritates the lungs of your mice and, with time, it will damage them. High ammonia concentration also increases the damage caused by certain virus, bacteria and mycoplasma that mice often harbor silently in their lungs. Ammonia diffuses away into the air. So the more air changes or airier the mouse room, and the greater the surface area of the bedding, the slower the ammonia will accumulate.If you put a sufficiently deep layer of bedding in a 20-gallon aquarium with two or three mice, you should not have to change it for up to a week.

What Temperature and Lighting Are Best For Pet Mice?

Mice handle cold much better than heat. They do best when they live in an environment that is kept between 65 and 80F. A reptile  thermometer  with a humidity gauge is a smart purchase.

Although mice are said to have sweat glands on their feet – I have not seen overheated mice sweat. Instead of drinking more, they retreat to a corner, hyperventilate and eventually go into a coma.

Mice do not like bright light. If your mice retreat into nooks and crannies too much, your lighting may be too bright.

Should I Buy Toys and Improvise Stuff To Keep My Mouse Occupied?


Mice love toys and hollow objects in their habitat. Ladders, mouse-size exercise wheels, old cardboard tubes, wool socks, small cardboard boxes and fiber egg cartons, are all appreciated by mice. They love to hide and burrow and, more then anything, they love to busy themselves build nests. Fabric and string remnants, shredded paper and soup cans all get converted into nests.Most objects you place in the cage are best discarded when they become soiled. If there are items to reuse – be sure they are easily soaked and washed.

Do Mice Bite?

They most certainly can. Fearful mice will bite if you restrain or grab them. Domestic mouse bites need to be treated as ordinary puncture wounds. They are not a source of rabies.

I Don’t See My Mouse Out And About Much During The Day – Why Is That?

Mice are most active at night or in subdued light. They also tend to come out when there is not a lot of racket, vibrations and noise in their environment.

Can I Potty Train My Mouse?

I have never successfully done that and I do not know of anyone who has. The function of the colon in mice seems to be continuous, with fecal pellets dribbling out one by one rather than accumulating into clumps that are evacuated all at once. But you mouse will tend to eliminate in a specific area of the cage – generally in a corner. In plastic cages, the ammonia released by that activity eventually degrades the plastic in that area.

Be prepared to occasionally receive little fecal presents from your mouse when you handle it. Just keep a paper towel or Kleenex near by.

What Is The Right Way To Pick Up A Mouse?

The proper way to hold and pick up a mouse is to grasp the base of its tail gently and slide it into a cupped hand. Be gentle. Do not let go of the tail until you are sure the mouse will not jump from your hand. Before you grasp the mouse, let it sniff your hand for a while. Mice do not have fantastic vision; they make most of their decisions based on their sense of smell.

Speak gently and move softly with mice. They have very good hearing and perception of vibrations. Loud sounds and harsh movement frighten them. They rely on their whiskers to feel and touch. Their whiskers are very sensitive to the movement of air. If the mouse is too frightened to cooperate, shoo it into a section of toilet paper tube, pick that up flat with the ends covered, and wait patiently for it to come out.

Little training treats are a good way to teach your mouse to go onto your hand unassisted and to come when called. Eventually, when it realizes it has nothing to fear from you, it will climb out of you hand and up your arm.

How Can I Tame My Mouse To Be Relaxed With Me?

Give newly purchased mice two days to get used to their new surroundings without disturbing them. Sleeping mice do not like to be disturbed. Wake them up gently by stroking them. If you are fearful you will be bitten, stroke them with a Q-tip. Most strains of domesticated house mice are not aggressive or temperamental. Don’t tower over the mouse. Think how huge you must appear to the little creature. Don’t begin this will a bunch of excited, noisy children in the room.

Mice learn surprisingly fast. Particularly when they begin to associate you with food snacks. Be patient, speak softly, have your training sessions at the same time every day. You may find you make more progress at certain hours than others. Mice have “ADHD” – short attention spans. Keep your training sessions short.

Can I Catch Any Disease From My Pet Mouse?

Although wild mice are a source of a number of dangerous virus and bacteria, properly maintained, domestically raised mice usually do not carry diseases that are a threat to people when they are purchased from reputable sources.

Mouse colonies that are unsanitary and that allow the mingling of domestic and wild outdoor mice can harbor salmonella bacteria and the LCM virus,  leptospirosis , giardia, cryptosporidia, and skin fungi have all occasionally been found in unsanitary mouse colonies. No species of pet animal is entirely free of organisms that, on occasion, infect people and mice are no different in this respect. These organisms are most often a threat to the very young, the very old, and people in general poor health with compromised immune systems. If you or members of your family have chronic respiratory problems or weakened immune systems, mice may not be a good choice in pets.

Do Mice Need Periodic Veterinary Care?

Traditionally, very few mouse owners bring their pets to visit veterinarians. Since not many veterinarians feel confident or knowledgeable about treating mice, bring your mouse in need of veterinary care to a veterinarian experienced in treating “pocket pets”. If you bring your mouse in for a check up, the veterinarian will examine it for external and internal parasites and treat them appropriately. Dealing with more complicated health issues is a challenge because mice are so small.

Also, because mice are so small and fragile, problems need to be recognized early and treated if the mouse is to have a chance to survive. If a mouse appears unhealthy, it is not likely to improve on its own without some form of treatment.

What Signs Of Illness In A Pet Mouse Am I Likely To See?

1) Weight loss

2) Reluctance to move

3) An unkempt hair coat

4) Frequent scratching

5) A tucked up tummy and hunched posture

6) Raspy breathing and sneezing or chattering

7) Nasal crustiness or discharge

8) Soiled anus or runny or poorly formed stools

9) Skin abrasions, discolorations or wounds

10) Grinding of teeth

11) Limping

12) Lumps and bumps

13) Distended abdomen

14) Squinting, eye discharge or clouding of the eye

Most of the problems that cause poor health in younger mice are related to husbandry. Wounds are often the result of fighting. Poor or inappropriate diets, stale air/ high ammonia, crowding stress, and over breeding all take a toll on health.

Occasionally mice get stepped on or handled roughly and suffer broken bones. These can be splinted and generally heal well.

Veterinarians can also neuter male mice and female mice can be spayed – I did these procedures frequently in a laboratory setting but it is rarely done in private practice.


There are tests available to detect the common virus of mice – but if confirmed, these there are no practical individual treatments for a pet mouse.

Many of the problems mice suffer in old age also do not have practical solutions. Because mice age so rapidly, we see a lot with tumors. Kidney failure is also a common problem in older mice. I have an online article on treating kidney disease in elderly rats. You can read it here and the treatments are equally applicable to mice.

Occasionally, a mouse will have an abnormal jaw bite. The mouse’s upper and lower incisors must be in perfect alignment to wear evenly. When this is not the case, your veterinarian need to occasionally cut them off short with dremel-type tool. Read about that procedure here.

Breeding Mice

Mice can breed when they are very young. Female mice are sexually mature when they are about six or seven weeks old and males a week or so later. Occasionally, female mice as young as five weeks have the ability to become pregnant. It is not wise to breed mice until they are three months old. Once they approach a year old without having had a litter, it is best if they are not bred.

Once female mice reach breeding age, they cycle every 4-5 days if they are not bred. Their fertile period lasts about 12 hours. They can breed any time during the year. They usually breed at night. You can tell when a female mouse has been inseminated by looking for a distinctive, waxy , cream-colored vaginal plug. This plug is present the evening they mate and the following day. Then it drops out.

Pregnancies in a mouse last 18-21 days and their litter size is generally between 4 and 15 pups. Females are capable of having five to ten litters a year. The baby mice or “pups” weigh 0.5 – 1.5 grams; it would take about four pups to equal the weigh of a sugar cube. They are bright pink at birth and without hair. Their eyes and ears are sealed shut. Their eyes will not open for another 10-14 days. During this early period (2-3 days), mother mice should not be disturbed. When they are, they have been know to eat their babies. They will continue to nurse their babies for the next three weeks.

Mother mice have a fertile period 14-24 hours after giving birth. If they are not bred then, they will become fertile again a few days after they wean their pups. When two or more female mice are kept together, it is not unusual for them not to cycle at all. If you add a mature male to the group, the females will resume cycling in a few days.

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