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The Fun Mouse: Mouse Information: Caring for babies, birth through weaning.

If you haven't done so already, please read the Breeding Ethics page before venturing further. Mice are NOT TOYS!


Important Introduction

By the time you get here, you should have already read the Breeding Ethics page as well as all the other topics relating to breeding in the Mouse Information section of the site. If you haven't already, you should also have an Emergency Kit prepared. Additionally, you should fully respect your mice as LIVING creatures just like you. When making decisions for your mice, always ask yourself, "Is this what I would want for myself, should I be a mouse?" Does that sound extreme to you? Would it if you were at someone elses mercy? Are you secure enough in your actions to even ask yourself that question with all seriousness?

By no means does this section cover everything you should know before breeding. It is set forth as an outline for those that have been thrown into breeding by means such as pet shop "accidents" and things of the like. Should you intend to become a breeder, you will need to know far more than the basics here. No matter the cause, if you are expecting a litter, we also recommend that you read everything on health care you possibly can. This site is a good start, but never limit yourself to just one source. There are many other great resources out there too, such as those on the Links page.

Breeding is a risk no matter what way you look at it. It is possible for everyone involved to die, including the father (while rare, a doe may bite the buck during mating, causing severe damage and possibly death. Obviously aggressive behavior should never be passed on/bred from). Everything you do, and don't do, has its own risks. Your job as a good caregiver is to educate yourself and take the fewest amount of risks possible with every case that may arise. Evaluate each situation quickly and efficiently. There often is no clear-cur 'right' answer, especially when it comes to things like breeding complications. All you can really do is; 1- Educate yourself so you know how to handle the most amount of situations possible. 2- Know the statistics (odds of a good or bad outcome) resulting from any kind of action you choose to do, or not do. 3- Understand that while it can be hard sometimes, it's best to choose the action (or no action) that is the least riskily for a given situation. Taking unnecessary risks is unethical and usually done for selfish reasons. You must place the animals before anything else.

If at any time you don't feel that you are able to properly care for your mice, please seek help. There is NO shame in seeking help. There is, however, shame in not seeking help when you need it. can be a good resource for re-homing mice and getting them the care they need and deserve.

End of pregnancy, beginning of birth.

During the end of pregnancy most does look unmistakably pregnant while some others may look no different in appearance. In the last few days of pregnancy you may notice that the mother is very uncomfortable, stretches a lot, doesn't move around as much as before, has slightly stressful breathing (not to be confused with labored breathing caused by being ill. This will usually, though not always, include other signs of illness as well), etc. In the 24 hours leading to birth, you may even see the mothers belly and sides moving because of her babies moving inside her. Her sides may ripple very noticeably (contrary to some belief, this is not contractions). If you see this happen, you know delivery is nearing. Generally babies will come within 24 hours from the time you see the babies moving, should you be so lucky as to see this. There are no way for a fancier to know -for sure- that a doe is in labor. It is unlikely you will see her give birth. She should have them in a closed next box, out of your sight. Mice generally give birth at night also. If she has her babies out in the open, it is best to put a towel around her tank to give her enclosed privacy, leaving the top open for good air circulation, and leave the room. As tempting as it is to watch, she NEEDS her privacy at this time for her well being as well as the babies. If you watch her labor, it can become very upsetting to her and she may kill her babies. Please do not take this risk. The mother and babies have nothing to gain by you watching, therefore watching is selfish and a needless risk. Never disturb a mouse while she is delivering her babies unless there is an emergency *and* you are *positive* you can help. Most times the best thing to do is let nature takes its course though. Little can be done for a mother in distress and *nothing* should be done without vet consult.

Are they here yet?

First and foremost, after birth the mother should be left completely alone unless there is an emergency. Bothering the mother can cause her to kill her babies if she feels threatened (far more likely with skittish mice and untraced lines). Additionally, it is only respectful to let her bond with her babies without your interruption. Bothering the mother before the babies are 3 days old can be dangerous and it is extremely selfish (see: Handling Babies section of this page). Putting your desires above her needs at that crucial time is selfish and an unnecessary risk. Bothering the mother includes lifting the nest box to peak at the babies, even if the mother (and nanny) are not in there. The only thing you should be doing in the 3 days following birth is feeding, watering, and spot cleaning *only when necessary*.

Don't worry about not knowing if the babies are born if you can't look. You will know. Some litters are extremely vocal. This is completely normal and should not cause you alarm. If there is something wrong, you will hear obvious screaming. There is no mistaking it, even to a first time breeder. It will send chills down your spine. If you hear squeaking, you know the babies are born and doing fine. Also don't worry if you don't hear the babies chirping. Some litters are loud, some are completely silent. Some only squeak when they fight over nipples. Another way to know if mom gave birth is that momma will likely spend all her time in the nest for quite a while after having her litter. You will likely not see her for 24-48 hours after birth (don't worry about her getting food and water, she will be okay as she knows what she is doing). After that you will see her out often and she will likely be thinner (losing the 'baby bump'). Mothers tend to spend a lot of time outside the nest. Some mothers only go in the nest to feed the babies every so often and that's all. Don't be alarmed if she isn't in the nest very much after the babies are 1-2 days old. Mouse mothers are less attentive than us humans think they should be. It is common for inexperienced people to be alarmed by a seemingly inattentive mother. However, this is normal and everything is likely fine. If you are using a nanny, she will likely be in the nest far more than mom. Don't be worried that the nanny is stealing the babies unless you hear the nanny fighting with mom and not letting her with the babies at all. It is perfectly normal for the nanny to be very attentive to the babies and mom to only pop in and out to feed.

Postpartum Estrus

A female can come back into heat within hours after giving birth. This is called "postpartum estrus." If a male is with a female when she gives birth, it is extremely likely that he has mated her again. This will result in a back to back pregnancy. The second litter will likely be born before her first litter is fully weaned. The first litter shouldn't be weaned before 28 days, yet the second litter will likely arrive at 20 days. This will usually force the mother to wean her oldest litter faster, which isn't good for their health. Additionally, the second litter will be weaker because all the stress on the mother. It is shown that babies resulting from a back to back pregnancy will live shorter lives and have far more health problems than babies born to a mother that didn't have a back to back pregnancy.

If a male mouse is left in with a female when she has her babies he may react in a few different ways. He may kill the babies. Male mice have a couple reasons for doing this. If he doesn't recognize the babies as his, he will kill them so he can impregnate the female with his babies. This insures his genes' survival. He may also kill them because he is jealous. Sometimes a male will kill the babies because he feels that they are taking the moms attention away from him. It is possible that he will ignore them entirely as well. This is doubtful but possible. Lastly, he might be the world's greatest dad. Male mice are amazing creatures when it comes to fatherhood. In many species the male will abandon or kill the babies all of the time. Mice, however, are the opposite. Most of the time a father mouse will be very supportive of the mother and their young, so long as he knows they are his kids (a male actually has an internal clock of sorts, which will tell him if the babies are his based on conception date and birth date). A male is usually a better "nanny" than a female nanny. However, leaving him in with the mom almost always insures that the mother will get pregnant again after having her litter. This is very hard on them all and can cause serious health issues, as stated above. A father should never be permitted to live with a mother and babies. It is an unnecessary risk that is proven to decrease vigor which is the opposite of what a good breeder will breed for.

Birthing Complications

If the mother is having babies all over the tank and they are coming out alive, it is likely that she just doesn't know what to do (if they are coming out dead, see below). If this is the case, don't disturb her. Put a towel or blanket around her tank (but not over the lid of the tank) and leave the room. Hopefully she will put them in her nest and take care of them. Hand raising should be the very last resort. It is best to give her every opportunity to take care of the babies and not intervene. However, if they are dying from chill (not to be confused with them being stillborn) or she is killing them, fostering or hand raising may be an option. If she is abandoning them, you can try to place her babies in her next box and hope she then accepts them. Doing this is a risk because she already abandoned them once. If you choose to do this, make sure mom is done having babies, remove her from the tank and place her out of sight. Then place the babies into her nest box. Once they are settled, place mom back into the tank (but not into the nest box). Alternatively you may be able to foster the babies with another mother. If you have another doe with babies the same size as hers, you may choose to foster them with her. See the section on fostering babies in the Caring for Orphan babies section of the site for details on how to best go about fostering and all the risks involved. If a foster mother isn't an option, you may choose to hand rear. However, this has minimal success rate for babies so young. It is likely that they will all die (older babies have a chance, but for new born babies death is very high). Hand rearing will extremely stressful to you as well. You will not sleep for weeks, literally. You will watch many, if not all, of these babies you've come to love die. It is more painful than one can describe. The bond you develop with these babies will be overwhelming and very heart breaking if they pass. If you hand rear, understand that the babies will need to eat every 1-2 hours. If you can't be with them every 1-2 hours for feeding, you can't hand rear the young. There is no shame in this. Most people are not able to. However, if you can't, don't bother mom -at all-. Let nature take its course. The mother might take care of them, or she may not. But it is up to nature at that point. If the babies by some chance are struggling along hours after she had them, she refuses to take care of them, and there are not other options for the brood, humane euthanasia is in order.

Excessive Blood;
Abnormal bleeding means that there is a severe problem. Note that some blood is normal, however, a lot of blood isn't normal. Several pieces of bedding that have blood on it isn't alarming, a lot of blood on many pieces of bedding is not normal, especially if these pieces of bedding are all over the mothers tank. If there is a complication like this you will very likely see abnormal blood outside the nest box. Don't confuse blood from culled babies (babies that the mother has cannibalized) with excessive bleeding. Don't panic and don't bother the mother unless you are sure that she truly is bleeding too much (call your ER vet if you are unsure). The odds of her harming the babies if you invade her nest box are higher than those of her having birthing complications. Therefore, it is better to leave her alone and only worry if you see blood all over the tank. If a mother is bleeding out, she will die in a very short period of time. A vet may be able to help, but it's not likely she will survive even with prompt vet care. If you see this happening you have the same options as the situation below.

Sill born;
If the babies are all coming out dead, this is a sign of complications. Sometimes a mother will expel her dead babies okay, while other times a baby may get stuck, blocking any births from proceeding. If there is a blockage, it will almost always result in death of the mother. Death will occur within 24 hours (she will also run a fever, but you will not likely be able to tell). When a mother has an abnormal number of still born babies, the chance of a baby not being birthed his higher. Just like above, the odds of her harming the babies if you invade her nest box are higher than those of her having birthing complications. Therefore it is best not to invade the nest to check on her. IF there is a problem you will likely see evidence in the tank without having to invade the nest. If there is a complication, see below.

ER care;
If you see your mouse bleeding abnormally or giving birth to all/mostly dead babies, you have 2 options. You may rush your mouse to a vet for a Caesarian section, or let nature take its course. If the vet is already going to perform invasive surgery to expel the babies, the mouse should also be spayed. A mouse that has birthing complications may NEVER be bred again. If she is, the chances of repeat complications is extremely high and the pregnancy will likely cost her life. Spaying will also help her live longer, by decreasing her chances of getting different cancers, among other things. However, at the present time, spaying a mouse is just as risky as letting nature take its course. This is provided that you have an experienced vet that has actually spayed a mouse before and has the proper equipment. If your vet does not, then her chances of surviving the surgery are less. It is up to each mouse caregiver to decide which, a caesarian or letting nature take its course, is the better option. As of right now, there is no right answer to this as the risk is the same no matter what you choose.


Cannibalism is not to be mistaken or treated like a birthing complication (i.e. meaning that you can attempt re-breading). Sometimes a mother will eat some, or all, of her babies. This is sad but it is a fact of life. There are a few reasons this can happen and some we simply don't know. One reason can be that she lacks a proper diet with adequate protein and fat boosters. Another reason is if she doesn't feel that she can adequately care for them properly due to her own inexperience or being fearful. In these cases she will cull them as humanely as she knows how (culling quickly is better than alternatives that may hurt more). Additionally, animals know if their babies are healthy or not and a mouse will eat her young if she feels they are not healthy. Many times this will happen to the runt of the litter. If the mother culls a runt or unhealthy offspring keep in mind that nature works in ways that seem strange to us humans but mom mouse does know best. A mother always has a reason to cannibalize and will do what is best by them, even if we never truly know why she culls them. Animals don't like to see suffering, especially their own babies. They would rather take them out of their misery as fast as possible than let them suffer. For instance, if a mother doesn't feel she will have enough milk to feed her babies, she may cull her litter down to compensate for that. Another case where a mother might cull her babies would be if she feels that her babies may be harmed by a predator, including a human. In those cases she does her best to make death as quick as possible, quicker than a predator likely will. You also have to keep in mind "survival of the fittest." In order for a species to survive, only the strong can live. Unlike humans, animals have a better instinct of which ones are strong. To preserve the species, they will sometimes weed out the less healthy. However, mice are so domesticated that they have lost much of this instinct. You likely would never know why she did it, but mom does. Never doubt that mom knows more than you and never be mad at mom for doing what she feels is right.

Sometimes a first time mom will eat or kill her entire litter. This is commonly known in the fancy as "first time mom syndrome." No one is positive why this happens (other than the possible reasons given above), though it does happen much more often with untracked lines. If you have a first time mom who has killed her babies (and shows no signs of complications), don't hesitate to breed her again after she recovers. Keep in mind that a mother that loses her litter needs MORE time to recover than a mother that has a successful litter. Nature is an amazing thing. There are several things working together to help both mother and babies be as healthy as possible. For instance, when babies suckle from mom her uterus contracts, going back into place. This helps her recover faster. If she doesn't have that suckling stimulation, it will take her body longer to recover. You can't see this from the outside. This is only one of many examples proving that mom needs babies almost as much as she needs them. When she is ready to be bred again (if you choose to, and she is able), she will probably be a great mom the second time around despite her first litter.

Cannibalism also happens after a mouse has died. Some people find one of their babies half eaten and assume that the mother killed the baby. This is not necessarily the case. It is possible that the baby was already dead before the cannibalism. Mice are very clean animals. When one mouse dies they feel the need to clean up after him or her. A mouse's way of "disposing" of the body is to eat it. If they don't eat him/her, then they will often burry him/her. A mouse in a tank can't remove the body, so they do what they can to take care of the situation. I know it's hard but try not to let it disturb you if you see it happen. Do, however, remove the carcass.


Some litters have no runts while others have one or more. The larger the litter, the higher the chance of having runts. Sometimes people never see them because the mom disposes of them before they get the chance. Some runts can live very long happy lives, while many of them pass early on. Mouse moms, like other animals, often (though not always because we have successfully bred 'nature' out of the mouse, unfortunately) know when their baby is not healthy and may choose to do the most humane thing, which is taking their life early on before they suffer later. This is their way of preventing their young from experiencing a harder life or a miserable death. Keep in mind that this is natures way and "mom knows best." Some runts that make it to weaning may still live shorter lives (this isn't to discount the few that live normal lives though). Some runts have been known to live several months and then un-expectantly pass away for no obvious reason and to no fault of the caregiver. Average/Runt/PeanutOn a newborn or baby is hard to perform a necropsy and actually see anything because of how small the bub is, therefore it is not readily practiced by vets. We can fairly confidently assume that something was under developed or never developed right. For instance, if the heart or lungs are not developed right, then the baby might live for quite a while before it stops, or the mouse might die at birth. If you have a runt that has un-expectantly passed away for seemingly no reason, keep in mind that this kind of thing happens and it's not your fault.


A peanut is around half the size of a runt and will never live past weaning age. Some people (even the most experienced breeders) mistake runts for peanuts, thus they think they can live longer but in reality they do not. Sometimes it can be hard to tell a runt from a peanut, especially if there are not both in the same litter (like seen in the picture to the right. Click the image to see it larger). Peanuts are very underdeveloped and never thrive. When mom weans the peanut off milk the peanut will always die no matter what one tries to do to help them thrive. They will become very anemic, often shake, become lethargic, etc and waste away. As with runts, some mothers will dispose of peanuts. If mom doesn't cull them it is best that you, as a responsible caregiver, do so in the most humane way possible. It is not fair to the baby to suffer so horribly before they inevitably die.

Handling Babies

While taking special precautions, you may hold the babies when they are 3 *full* days old. 3 days after birth is often mistaken for 2 days. However, the day they are born is NOT one full day it is a partial day, thus should not be counted as a full day. Babies are 3 days old when they are 72 hours old, not 48 hours and some change. Holding the babies too young, or not taking the proper precautions, can result in the mother killing or abandoning the litter. Additionally, giving her time to bond with her babies after birth is one of the most beneficial things you can do for their health and well-being. A better bonded mother that doesn't have disturbances in the first 3 days has a better chance of being a better over-all caregiver to her babies. Bothering the nest too soon is not only a risk, but it's very disrespectful to the mother (no matter how much someone 'thinks' they know their mouse). While it is tempting to peek, the best thing you can do for mom is to leave her alone. Doing otherwise is extremely selfish as it only fulfils your personal curiosity and rarely does anything for the mother and babies. The only exception is if there is an obvious complication and you are *truly* able to help (which should always be known before making the decision to intervene). Only a very experienced breeder that knows how to recognize distress situation and is *able* to handle those situations should even attempt to take a risk, and they should only do so when there is a high risk litter (such as hairless which have trouble lactating).

When holding the babies for the first time, take the following precautions:
1) Have a play tank ready for the mother and nanny (if a nanny is used). This play tank shouldn't be too large, but should contain some toys. It also helps to add some yummy, yet healthy, treats to distract them while you are holding the babies. Cheerios are one of many good options.
2) Wash your hands extremely well with antibacterial unscented soap.
3) Wait for both mother and nanny (if a nanny is used) to leave the nest box. This may take time and patience. However, never go barging into her nest box. That is her safe spot. Intruding in on her nest box while she is in there can make her feel insecure, possibly making her abandon or eat her babies. It is okay to try to coax them out with a yummy treat.
4) Move both mother and nanny into the play tank. Make sure they are secure in there and can not see or hear the babies.
5-a) If you wish to rub your hands in clean bedding from the moms tank so you smell like them, you may do so now. However, it is a myth that mothers will abandon their babies if they smell like a human with clean hands. It is never good, however, to hold them with scented hands (such as scented soaps or lotions). The reason you should never have artificial scent on your hands is because of their sensitive lungs and skin (from possible residue).
5-b) With warm hands, pick up the babies gently. Hold them as a group and only for short periods when they don't have fur. Pinkies can chill extremely fast. As they get fur, you can hold them longer and individually if you wish.
6) Place the babies into the nest exactly how mom had them.
7) Fill the moms food dish, water bottle, and give her the booster food.
8) Spot clean the tank if necessary.
9) Return mother and nanny to the tank and leave them alone.
10) Wash your hands again.

You should always remove the mother and nanny from the tank until the babies are weaned. Not doing so is a risk to the well being of the babies. It is not unheard of for a mother and/or nanny to attack babies that have been taken from their tank (while mom and nanny are left in their tank) upon being placed back with them. Understand that mice have extremely poor eye eight. Imagine being almost blind and having a bunch of people come running into your home. What would you do if you had small children at home? Instinct of both human and mouse is to defend their babies. Sadly, sometimes it is done by mistake (for instance, more guns in the home kill family members than 'bad guys.' Just the same, mom might mistakenly attack her babies. It's the same thing). If this happens, it isn't the mouse's fault. It's the humans fault for not knowing better. This is natural instinct to protect the young. It is best, however, never to breed from a mother (or her offspring) if she dos this. Our job as breeders is to breed all 'aggressiveness' out, making mice as docile as possible. This is removing the nature from the mouse.That's a lot of what domestication is.

Cleaning the Nursery

Ideally, the nursery tank should be set up around a week prior to mom giving birth and have the last cleaning 2 days before mom gives birth. After the babies are born you should not bother anything for 3 days, other than to feed and water. In that time, should there be wet/soiled bedding that needs to be removed, quickly and quietly do so but only when necessary. On day 3 you should begin spot cleaning every day. It is easiest and best to do this while mom (and nanny) is in the holding area during the time you handle the babies. You should fully clean the tank (but NOT the nest) when the babies are 1 week old. The nest can be spot cleaned if it really needs it, but otherwise leave the nest completely alone until the babies are at least 2.5 to 3 weeks old. Some will even wait until the babies are 4 weeks old and weaned. A mother will generally keep her nest very clean, spot cleaning it herself. If at any time the nest is soiled to the point that it becomes a health risk, it obviously needs to be cleaned as the risk of not cleaning it is higher than cleaning it. Use your better judgment here. Try to leave as much of the old bedding in there as you can, while still removing anything soiled. While cleaning the nest, if needed, move the babies to a safe spot that also keeps them warn (but not hot!). Do not place the babies where the mother (or nanny) can see them. Temporarily placing them in a kritter keeper with fleece and shredded kleenex will work.


For the tamest, most loving, and social babies you should to hold them at least once a day from the time they are 3-4 days old. Holding them daily also helps insure they are healthy because you will get to know their personality and growth rate, thus you will know sooner if there is something wrong. Even the most experienced breeder can't catch things sooner than someone that knows their mice well and handles them daily. When it comes to tameness, there is a lot to be said for both nature and nurture. Mice will take after both parents. Even though they don't know their father, his personality traits will be passed on to an extent. Some odd behaviors of bucks can be tracked through lines even though the babies never meet their father. Breeding tame parents greatly helps insure tame babies. Nurture also plays a large roll. Nurture is the love you give the babies to tame them. The more you handle and love the babies, the tamer and more adjusted they will be. The more they are tamed and the more exposure to humans they have, the easier time the will have going to new homes as well. The more things they are exposed to helps them accept change much easier. Environment also plays a roll. If you use a nanny, the babies will pick up on her behavior and the mothers behavior toward you (learned behavior). They will mimic what they see when the adults interact with you. The tamer they are, the tamer the babies will be. If the babies see how much the adults love you, they will not be frightened. Their outside environment (i.e. the room they are in) also plays a part in how tame and accepting they are. Playing a radio in a quiet room will get them used to sounds not native to your home. A radio should be played at a normal level, not too loudly. A radio is also said to reduce cannibalism, per lab observations. Unless there is an extreme circumstance, mothers and babies shouldn't be kept in too quite of an area, or an area with too little traffic. If they are never exposed to these things, they will have a harder time adjusting to new things and taming will take longer. Mice should never be kept in a loud, extremely high traffic area either. Mild noise, mild traffic, and a setting 'normal' to the mother is the most ideal (unless there is a birthing complication).

Popcorn Stage (aka Flea Stage)

The popcorn stage is where the babies bounce around, much like popcorn in a popcorn popper. This stage starts around the time their eyes open, give or take a couple days (some reference the babies as 'hoppers' at this stage in their development). At this stage the babies have no fear of falling, as if they don't grasp the concept that it can hurt them and they are oblivious to what they are doing. They pop for an array of reasons. Everything is very new to them. New sights and sounds can startle them easily, just like a new born human baby will throw their hands in the air suddenly when they are scared. Some mice will popcorn for seemingly no reason. Some will popcorn when they feel a sudden movement, such as one of their siblings popping or just moving. It is extremely important to hold popcorn babies by the very base of the tail, gently yet firmly. Also hold them over something soft, such as a box filled with something soft like bedding. It is best not to hold popcorn babies over nothing or high up. Should they get away, you will likely never retrieve them. If their eyes are open, don't hold them over their nest box or tank. This is an incentive for them to jump into their home and will only make the stage worse. Make sure you also cup the baby in your hand at all times. Allow room to breath but not jump out. Pet them and comfort them with a soft voice. Do not hold more than one popcorn baby at once. Doing so only increases the risk of them jumping out of your hands. The popcorn stage lasts for around 1 week, on average. Severe cases can last a couple weeks and if not worked with, they may never become tame. Once they emerge out of the popcorn stage they grow into what can be compared to human childs' terrible 2 stage. This is when they want to explore everything. They are like puppies and have a lot of energy to burn off. They will play a lot. They start growing out of that stage around 5-6 weeks of age.

Some mice go through worse popcorn stages than others. Pet shop or poorly bred mice often go through a horrible popcorn stage which can even include biting. Biting is NOT okay. Any mouse that does this should not be allowed to pass their genes on (and you may even consider not breeding the siblings either). Babies that go through a horrible popcorn stage can be very trying to the patience and dangerous to the pups. However, not all mice will go through the popcorn stage at all. Mice from well bred lines often don't go through a popcorn stage at all. This is one of many drastic differences between pet shop mice and well bred mice. Well bred mice have the "fright and flight" bred out where as pet shop and other poorly bred mice still have that instinct well intact. This can lead to not only horrible popcorn stages, but a flighty mouse throughout life. Mice that go through a horrible popcorn stage need to be worked with at least once a day, if not 2 times a day. They will never be as tame as well bred mice, but they can be lovely companions if worked with well enough.

Mounting Behavior

It is perfectly normal for siblings to mount other siblings (bucks mounting bucks, bucks mounting does, does mounting bucks, and does mounting does) and mother mounting babies (both bucks and does). This is behavioral, NOT reproductive. If you see this, don't panic. If the babies are under 4 weeks old, no offspring will come of this behavior. Mounting is contributed to a couple of things. In part, it is due to establishing dominance. The one doing the mounting is trying to assert her or him self as more dominant than the one being mounted. When the mother mounts the babies is is done sometimes to assert dominance to her ever independent babies and sometimes to show the babies how to mate. While this seems odd to us, think of it like her teaching them about 'the birds and the bees.' Us humans can talk to communicate, where as animals rely heavily on body language. While it seems odd to us, when you understand that they can't sit down and talk about it, it helps us realize that this really isn't the odd. It's necessary to do it this way as they don't have an alternative. This is actually extremely important behavior and a necessary step in their 'education,' if you will. Studies will reflect that animals weaned too young sometimes never reproduce due to simply not understanding how, or not developing the drive to. This is heavily contributed to their mother never being able to teach them. This is one of many reasons that proves how important it is to leave the mother with her kin until 4 weeks of age.


The weaning process begins when the babies open their eyes at 2 weeks (give or take a few days) and will be completed by the time they reach 4 weeks. As their eyes open they will begin to explore and nibble on adult food as well as start tasting the water from moms bottle. You needn't give the babies anything special to help them onto adult food and you needn't worry about them learning the bottle as mom will teach them by example. As they begin eating adult food, they will decrease their milk intake. They still need to remain with mother until 4 weeks of age as she is still providing them with necessary milk and teaching them about life. Note that just because you don't see mom nursing it doesn't mean she isn't. You can not possibly watch them 24 hours a day to know exactly what is going on. As the babies grow, the mother will slowly wean them off her milk. They will be fully weaned by 4 weeks. At this point you MUST separate the bucks from the does. If the bucks are not removed at 4 weeks of age they may impregnate the mother and their sisters. Do not panic when reading that and separate them too early. There is no reason to panic. Those babies need to be with mom until 4 weeks to be as healthy as possible. Separating even a few days early can prove negative (as outlined in the section above), even deadly in extreme cases. Mice can not reproduce until after the 4 week mark (some older), thus separating them on 4 weeks to the day is the safest time frame possible. On the extremely rare occasion that someone has "claimed" that a 4 week old impregnated the mother or siblings most, if not ALL, cases it has been because the caregiver simply didn't keep track of their age well enough (i.e. the litter was actually over 4 weeks of age). There is a risk to both separating before 4 weeks and waiting until after 4 weeks. 4 weeks, to the day, is the safest possible time to separate the bucks. This isn't to say that separating younger will always result in death. That isn't the case and sadly some individuals pull babies too young, not realizing the harm they are doing. The healthiest and most well rounded babies remain with mom until 4 weeks of age. It is also beneficial (though not 'necessary') to leave the does with their mother for at least an additional week. Breeders have noted increased health and docile nature when practicing this method of caregiving.

If your litter is from pet shop lines or anywhere other than well tracked lines from truly well educated breeders, it is advisable to separate all of the bucks into their own enclosure at 4 weeks of age. Most bucks will fight anytime beginning shortly after weaning. This is a natural behavior. Bucks in the wild don't interact peacefully with other bucks. If a buck crosses over into his territory they will fight to the death. In captivity this is true as well. Once their natural hormones kick in they will fight, even with their male siblings. Fighting usually occurs without any notice whatsoever! One day they will be cuddled together sleeping peacefully and the next day one or both will be DEAD or seriously maimed. Please don't take light of this! Time and time again there are cases where people ignorantly leave bucks together because "they are acting fine," they think "it would be cruel to separate them because they get along so well," and "some 'other' sites say bucks can live together" when in reality this is incredibly wrong and completely ignorant of the facts. Sadly there are many ill informed, though well intended, sites out there. Pet shop lines (and many from great breeders as well!) will kill each other if left together simply because of natural instinct. Leaving them together until they "show signs of fighting" will often result in death as they usually don't show any signs at all. It does, in fact, happen that fast. Additionally, this stands for mice *all over the globe* not just in one region. With that said, some breeders around the world have be enable to breed some of the instinct out of them, allowing the bucks to live together. This is more common, though not limited to, countries that have had domesticated mice longer (such as Europe) as they have had more time to breed the instinct out. Unless your mice come from a *good* breeder that *truly* is educated and they have been breeding a line for a substantial amount of time, don't trust that the bucks will live well together. Also, just because there are some (few) breeders out there that have been able to house bucks together it doesn't mean you will. Even lines that have some success being housed together will sometimes have problems, not to mention that bucks that have been breed often can't be housed back in a community. Risking it is NOT worth their lives!! Additionally, a novice should never attempt to allow bucks to live together, no matter the line. Leaving bucks together (with the slim exceptions stated previously) is an unnecessary risk. It is inhumanely playing with their lives. Bucks will have a happy life solo. They will also be better companions to you, as you will then be their only friend. Please don't take that out of context, apply it to all genders, and leave a female alone though. It is cruel to leave a female alone unless there are extenuating circumstance, which is very rare. If you want a single mouse, get a buck. If you want a colony, get does. If you don't have room to house bucks separately, don't breed and don't acquire more than you can handle. There's no good reason reason to risk their lives by housing them in settings that is not safe or in their best interest.

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