Male mice cannot typically be housed with other male mice due to aggression. Typically, once male mice hit maturity at between 8-12 weeks, they will become aggressive to those of the same sex- including littermates that they were previously raised with. This is simply the natural nature of male mice. Some breeders specifically work to "breed the aggression" out of male mice. However, whether or not these attempts have been entirely successful is much debated. It seems that all it takes is one overclean of an enclosure, or a male being temporarily isolated for medical purposes, for the male mice who had previously been living in harmony to turn on each other and begin brutally fighting once again. Additionally, it seems that breeding for reduced male-to-male aggression significantly decreases the fertility of males, to the point where many seem incapable of properly breeding. Therefore, these lines tend to burn themselves out quickly, and do not appear to be sustainable. It is also noted that some breeders claim to breed for male-to-male aggression, and yet adopters still note aggression and dominance behaviors between socially-housed males. 

Most breeders do NOT breed for reduction of male-to-male aggression, due to the associated fertility issues. Therefore, unless your breeder has given you the specific go-ahead, you should always plan to house males separately. Additionally, if you do decide to get male mice from a breeder who claims to specialize in reduction of male-to-male aggression, you should always have a clear back-up plan, just in case things change suddenly. Once male mice begin to fight, the fighting will often escalate quickly. 

When housed together, males will typically fight, and this fighting is often incredibly brutal and potentially fatal. Male mice often go into fights with the intention of seriously maiming, or even killing, the opposer- and sometimes, they are unfortunately successful. Common injuries due to socially-housed  males include, but are not limited to: nicked, torn, or completely ripped off ears - deep wounds to the neck, chest, belly, and rump - serious wounds to the genital areas, including castration - serious injury to the tail, including degloving - among other serious injuries, and even death. Often times, even if a male mouse survives an altercation, he may require intensive veterinary intervention, which is often incredibly expensive and difficult to obtain. 

Therefore, male mice are typically housed solitary. However, being social creatures, it is incredibly important to give solitary male mice lots of human affection on a regular basis. It is typically recommended to give your male mouse at least 15-30 minutes of one-on-one human social interaction per day if he is housed solitary. If you cannot provide lots of interaction for your male mouse, there may be other options for your situation. One option is to have your male mouse neutered by a licensed veterinarian, then house him with female mice. It is important to remember that male mice can still impregnate female mice once neutered for up to 2 months, so you should give your male mouse plenty of time to recover and rid himself of retained sperm before you place him with female mice, should you get him neutered. There are some less-than-ethical breeders and owners who may recommend banding your mouse as a cheap and easy neutering option. This is where a tight-fitting elastic band is wrapped around the testicles, causing blood circulation to cease and the testicles to eventually die and fall off- and is common practice with various livestock. However, mice have completely different reproductive systems than livestock, and therefore this is not an appropriate method for them. Banding is extremely painful for mice, and has a high rate of life-threatening complications, as mice will chew at the painful band and may end up severely injuring themself in the process. 

Neutering isn't something to take lightly, however- it tends to be incredibly expensive, often costing hundreds of dollars. Additionally, even the best veterinarians cannot provide a risk-free neuter- mice are very small, sensitive animals and are extremely prone to anesthesia-related complications, as well as post-surgical complications (mice may chew at their incision, and it is impossible to place a cone-of-shame on a mouse). Neutering, even when performed by the best veterinarians, has an unfortunately high mortality rate. Therefore, neutering isn't always a good option for every owner or mouse. Another option is to house your male mouse with female African Soft-Furred Rats. 

African Soft-Furred Rats are a very similar species to fancy mice, and tend to get along with them incredibly well. However, obtaining them may be difficult, or even illegal. In some areas, it is illegal to keep African Soft-Furred Rats and other rodents of African descent, so always check for local laws and regulations before you decide to add ASF Rats to your home. Additionally, in some areas, there are little to no breeders of ASF Rats. ASF Rats are almost always bred to be feeders, and are not domesticated like fancy mice are. Therefore, most are jumpy, bitey, or downright aggressive towards humans, which makes them poor choices for those with inexperience, or households with children. 

Whether you have male mice or female mice, sometimes you will experience frustratingly-foul odors around your mouse's enclosure, causing a pestering smell in the room you house them in. The biggest mistake that new mouse owners tend to make when fighting odor is over-cleaning their mouse's enclosure. Mice have poor eyesight, and identify their enclosure and territory mostly by scent. Therefore, they mark their territories to feel comfortable and secure in their space. When placed in an enclosure that no longer smells like them, they may become stressed, and begin marking excessively. This is often the cause for the overwhelming foul odor that many new mouse owners complain of. 

Instead of doing lots of deep-cleans of your mouse's enclosure, instead try this routine:

• Take a few handfuls of used bedding from your mouse's dirty enclosure, and set them to the side.
• Empty the leftover dirty bedding. Clean sides and accessories with a neutral cleaner that doesn't smell strongly of chemicals, such as hot water and vinegar. For especially tough areas, try a safe enzyme-based cleaner, such as poop dissolver, which is sold for birds. 
• Check the wheel! Poop and pee on the wheel can stink up your entire enclosure, so if your mice have a habit of peeing and pooing on the wheel, try giving it a clean once every day or two to help keep your enclosure smelling fresh. 
• Place new bedding and clean accessories back into the enclosure, and set-up the enclosure as usual.
• Toss the bit of used bedding you previously saved ALL over the enclosure to reintroduce some of your mouse's smell and make sure they feel comfortable in their environment, preventing overmarking behaviors. 
• Consider opting for scent-absorbing beads or gels to put nearby your enclosure to help tackle bad odors. 
• Remember: Never use air or fragrance sprays near your mouse's enclosure, or light candles or incense in the room with them; It could cause a respiratory illness, such as upper respiratory infection. 

Female mice are incredibly social creatures- even more-so than their male counterparts. Therefore, it is incredibly important that they always have another mouse as a companion. Female mice should always be housed in groups of 2+. Ideally, they should be housed in groups of 3+, as these groups are more socially secure, and tend to thrive better. 

However, there are some instances where a female mouse may need to be isolated temporarily. For instance, if a female mouse is experiencing symptoms of a contagious illness, she should be immediately isolated from the rest of her group in order to protect the rest of the group from threat of infection. Another example would be a female who has been injured or received surgery, and therefore needs to be isolated to recover properly. Under both of these circumstances, the female should be isolated for a short period of time until they are in better health, then properly re-introduced to the colony. 

However, isolating a female permanently is never appropriate. Sometimes, well-meaning owners will isolate a female mouse who is displaying aggressive behaviors or fighting with her cage-mates. However, this is not an ethical circumstance for the isolated female. Sometimes, a female experiencing aggression can be calmed and properly re-introduced to her group. First, try these options : 

• Completely re-do introductions, from the start. Deep clean the enclosure, removing all possible sources of smell. Place a small amount of vanilla extract in-between the shoulders of each mouse, if possible. Introduce the mice in a small, neutral area, such as a carrier. Allow them to stay together for awhile before moving them into their permanent enclosure. 
• Try placing the aggressor with one other female mouse, preferably a rather docile one. 
• Try downsizing the enclosure to prevent the formation of individual territories and territorial disputes. 
• Try to identify any specific objects/accessories that the aggressor may be becoming defensive of, and remove them from the enclosure if identified, or in the case of necessary items such as water bottles, move them elsewhere in the enclosure.

If all else fails, and the female mouse cannot possibly be safely housed with other female mice, the most ethical option is often, unfortunately, euthanasia. It is not fair nor ethical for the aggressive female to live a life in isolation. She will become stressed, depressed, and unwell. 

You should always introduce female mice in a neutral space; Never simply place new mice into an already established enclosure. Choose a small space, so that mice are practically forced to interact with one another, without being so cramped as to force mice to be climbing over each other or risk hurting each other on accident (which could cause a fight). Depending on the size of the group you are introducing, you can utilize a carrier, large critter keeper, or bin. Make sure that the introduction area you use is secure, so that mice do not escape. Use fresh bedding to eliminate any smells, and do not place any items in the introduction area that could smell of your old group.

For the first 30 minutes or so, allow your mice to meet each other. As long as all goes well, you can then introduce food and water to the introduction area. Always supervise mice while they are meeting each other for the first time, so that if a serious fight breaks out, you can split them up and attend to any potential injuries. After an hour or so of smooth sailing, you are likely safe to place mice in their main enclosure. However, make sure to deep clean the enclosure first, and do everything you can to eliminate scents in the old enclosure. 

Some squabbling and dominance behavior is to be expected during introductions. However, you should become concerned if blood is drawn. 

Wheels are an amazing addition to any mouse enclosure, as they provide your mouse the ability to exercise and run as fast as they'd like, whenever they like! However, if you wish to provide a wheel, it is important to select an appropriate wheel for your mice. 

First, consider the type of wheels available. There are primary two types of wheels; Upright wheels, and "flying saucer" wheels. There are some reports of issues caused by saucer wheels. This is because saucer wheels tend to force the mouse to run sideways, causing some curvature to the spine, which could be associated with the same spinal issues as an upright wheel that is too small. However, there have yet to be any direct studies based on potential risks associated with saucer wheels. To be preventative, we recommend against using saucer wheels, and to instead opt for an appropriately-sized upright wheel. 

So what exactly makes an upright wheel appropriate? First, you should use a wheel that is solid. Some wheels on the market have bars or grates, which leaves mice the potential to get their nails or toes caught within, causing serious injury. You should always select a solid wheel to avoid this. You should also avoid any wheels with crossbars, especially if you have a group of mice, as this can cause injury as well. Next, your wheel needs to be the right size. For most mice, the minimum size is 8-10 inches in diameter. However, for some larger show lines of mice, a 12 inch diameter wheel may be in order. When analyzing if your wheel is large enough for your mouse, observe when they are running on their wheel to see if their spine curves at all. The mouse's entire back, and first half of their tail, should be mostly straight. It is acceptable to have a little bit of curve towards the middle and end of the tail. If you are concerned about the size of your mouse's wheel, just go bigger! There is no such thing as a wheel that is too big as long as your mouse is capable of moving it. This is unlikely to ever be an issue as long as the wheel isn't larger than 12 inches in diameter, which tends to be the absolute largest size necessary, anyways. 

If the wheel you are using is too small, it can be incredibly dangerous for your mouse. Over time, damage to the spinal cord can occur, causing pain and mobility issues. Mice can additionally develop a spinal condition called "wheel tail", which causes the wheel to curl improperly over the back, like a husky dog's tail. Even if the improperly sized wheel is removed, the tail will continue to degrade further down the spinal cord. Over time, this degradation can even cause paralysis. Remember; It is never acceptable to use a wheel that is too small for your mouse, and it is ALWAYS better to not use any wheel at all as opposed to a wheel that is too small or unsafe.

Now, what materials should your mouse's wheel be made out of? The basic answer is, something durable and easy to clean. The most common materials are plastic, wood, or acrylic. Acrylic tends to be the best option. It is incredibly durable and long-lasting, and very unlikely to ever need to be replaced. It is mostly chew-proof, extremely easy to clean, and doesn't absorb any pee or poo. Due to their higher quality, they tend to be silent, as well. However, it tends to be an expensive first-time investment. Plastic is also a reliable choice. It is not as durable, and is not chew-proof. Over time, it will begin to wear down, and absorb urine, so it needs to replaced every couple years. However, it is affordable, and also easy to clean and keep sanitary. Wood is a common material used with hamsters, but is typically a bad choice for mice. Mice are extremely likely to pee and poo on their wheel, and the urine and feces will leech into the wood and be difficult to clean. This will make the wheel unsanitary to run on, which could contribute to bumblefoot and similar infections. Additionally, it isn't just not chew-proof- being made of wood, it directly encourages the chewing. 

Free-roaming is by no means necessary to keep your mouse happy or healthy. It is typically better to directly handle your mouse rather than allow roaming. However, if you insist on free-roaming your mouse, you need to take careful consideration of their temperament. Many mice are stressed by free-roaming, as it is an unfamiliar location. They may immediately dart under furniture or appliances, making them near impossible to catch. This can be extremely dangerous for your mouse, and potentially cause harm to appliances, as mice can be known to chew on electrical cords, baseboards, and walls, causing property damage. 

Therefore, if you insist on free-roaming your mouse, it should be done in a secure location. Allowing your mouse to simply roam around the home is not safe nor practical. Instead, opt for a secure large play pen, or carefully block off a small room like a closet. Carefully consider if there are any furniture items, appliances, holes in walls, or other areas your mouse could gain access to, that could cause your mouse danger or be difficult to retrieve your mouse from. You should also ensure there are no chemicals, such as cleaning agents, insect baits, or other potentially dangerous substances. Carefully and securely block off any exit points your mouse could find. Remember; Mice are capable of squeezing through shockingly small spaces. If they can fit their muzzle through, they can likely fit their entire body through! Again, the safest way to free-roam your mouse is to only free-roam your mouse in a secure playpen with direct supervision at all times while they are out. However, it is an excellent idea to instead focus on your mouse's enclosure, providing new and exciting enrichment to explore. This will keep your mouse active, engaged, enriched, AND safe! This will also prevent your mouse from becoming stressed or uncomfortable due to not recognizing their surroundings. Additionally, if you do free-roam your mouse, all free-roam should be ceased if your mouse displays any signs of stress, such as hiding, squinting, jumping, squeaking, or any other negative/fearful behaviors.

So what about exercise balls? Won't exercise balls keep your mouse safe? 

Although exercise balls do prevent your mouse from getting loose, or getting into locations they should not be, they come equally with their own set of dangers. Exercise balls feature multiple small slits along their sides. This is designed to provide ventilation and allow the mouse inside to breathe. However, these slits do not provide nearly enough ventilation for a mouse, so the air inside will become warm, damp, and muggy the more time your mouse spends inside. Additionally, due to lack of bedding to absorb pee and poo, and lack of ventilation, the pee and poo that your mouse produces will become sickening ammonia within the ball, raising your mouse's chances of becoming sick, such as developing a URI (upper respiratory infection). 

Although they do not provide appropriate ventilation, these slits do provide something else- a possible danger for your mouse. These small, narrow slits provide the perfect place for your mouse's nails, toes, and tip of the tail to become lodged, and potentially be ripped off, causing severe injury. Couple these injuries with the amount of moist air, urine, feces, and ammonia in the ball, and you'll also see a severe risk of infection emerge. 

Lastly, these exercise balls are not pleasant for your mouse to be inside; They may be silly and enjoyable for you to watch, but your mouse is not enjoying the experience. Mice have extremely limited eyesight, and navigate their world mostly with their whiskers and sense of smell. Due to the ball, they are unable to feel their surroundings with their whiskers, or scent out their surroundings. The ball, being only semi-transparent, removes the rest of their vision ability they did have, making them completely blind. Most exercise balls also do not allocate enough space for a mouse's spine and tail, and just like an improperly sized wheel, this can cause spinal damage over time.

Already bought an exercise ball? Repurpose it! By sealing off the slits and hanging an open exercise ball from the top of your cage, you can create a fun hanging retreat for your mice to enjoy!

The best bedding for your mouse is typically a safe, shavings-based bedding sold for use with small animals. But why are shavings-based beddings better than paper-based alternatives? Aren't shavings unsafe, or even toxic?

There are unfortunately many misconceptions spread about wooden shavings and their use with mice, rats, hamsters, and other small animals. The reality is this- there is absolutely no scientific evidence to support that shavings-based beddings are unsafe, or otherwise bad to use, with small animals, including mice. In fact, research tends to show the opposite! Many misconceptions about shavings are based around factual information about specific types of shavings; Namely, cedar-based shavings. Cedar shavings ARE incredibly unsafe to use with mice, and shouldn't be used with them under any circumstances. Additionally, many beddings labeled as "softwood blends" also contain cedar wood, which also makes them unsafe to use. This is because cedar wood contains oils and phenols which are toxic in mice (and many other small animals). This can cause respiratory distress and neurological damages. 

However, other shavings-based beddings, such as pine, aspen, and hemp, do not suffer from these issues. Many people incorrectly believe that pine is also dangerous, alike cedar. This is again a misconception, based on two key points; Many softwood blends, which are primarily based with pine (usually), also typically contain trace amounts of cedar. Because of this, many people associate pine with toxicity, even though the true offender is the cedar, which they often do not know is in there. Because of this, when using pine, you should only use beddings clearly labeled as "pine shavings", not softwood shavings or softwood blends. Additionally, pine can contain trace oils and phenols if it is not dried correctly. Luckily, these oils and phenols are very easily removed when pine is kiln-dried. In the USA, all pine shavings sold for use with animals and livestock is kiln-dried; Therefore, any pine shavings you buy in the USA are completely safe! 

But why not use paper-based beddings, just to be safe? 

Because paper-based beddings come with lots of concerns! Paper-based beddings tend to be extremely dusty, which can cause respiratory distress in mice, and lead to respiratory issues such as URI (upper respiratory infection). Additionally, unlike shavings, paper does not absorb ammonia. Shavings soak in the ammonia, and dry it out, meaning that as long as you keep your enclosure cleaned properly, ammonia will not build up. However, with paper-based beddings, the paper instead simply becomes saturated in urine and feces. There is no absorption process that removes ammonia, so ammonia builds up. This ammonia is harsh and toxic, and can cause serious issues for your mice, and again, contribute to respiratory distress and URIs. 

It is acceptable to use a small amount of paper bedding in your mouse's enclosure, not to exceed around 30% of total bedding coverage. Some paper can be used to give mice more nest-building materials, and help burrows hold shape. Many mouse owners will layer paper bedding underneath and above two layers of shavings, creating a sort of oreo-like appearance- Shavings on top, paper in the middle, and shavings again at the bottom! It is important to ensure that areas where your mice are likely to urinate and defecate, such as in corners and around commonly-utilized hiding spots, have a good layer of shavings to absorb any potential ammonia. 

So what about bioactive?

Many people, especially those who have previously owned reptiles, aquatics, or plants, express interest in creating a bioactive mouse enclosure when they are first interested in mice. However, there are a few key reasons why "bioactive" mouse enclosures are not recommended, and may even be unsafe for your mouse. First, in order to create a bioactive enclosure, you must use a soil-based bedding. These beddings are just glorified dirt, which is really just glorified dust. These are not appropriate for mice, who should be on a bedding that is as dust-free as possible. Living on soil-based beddings will nearly guarantee respiratory issues such as URIs. Additionally, mice produce far too much waste and ammonia to ever safely live in a bioactive enclosure- there is no "clean-up crew" that can put up with the amount of waste they produce. The enclosure will quickly become unsanitary, and therefore unsafe for your mouse to live in. There are alternatives to bioactive enclosures! You can create a beautiful naturalistic look even with shavings-based beddings by using natural accessories, such as driftwood, cork logs and bark, hay, and natural sprays, which can create the natural bioactive look many owners wish for. You can also provide occasional access to a small container of soil-based bedding for your mouse to dig in and explore- though this shouldn't be 24/7. These are often called dig boxes, and can be an enriching occasional activity. If you are simply looking for a low-maintenance enclosure that you do not often need to clean, mice may simply not be the pet for you, as they tend to be a lot of keep up with in terms of cleanliness. You may instead be interested in reptiles, insects, arachnids, and aquatics- most of which often can have a low-maintenance bioactive set-up, if done correctly!

Once you've selected a bedding, you may be wondering how much exactly you should use. Typically, the more the merrier! Deeper bedding allows mice more opportunities to dig, burrow, and create complex tunnelling systems. Also, it gives ammonia more space to soak in and be absorbed, keeping your enclosure cleaner and more sanitary- which will reduce foul odors for you, and keep your mice healthier and happier! You should always use a minimum of 3 inches of bedding, though at least 5 inches is ideal. And, again, the more bedding you add, the better!