Sexing mice
Sexing mice is one of the most important skills to learn if you are serious about breeding or keeping large numbers of mice. You need to be able to identify and remove unwanted bucks from the nest at only a few days old, as well as to separate baby bucks from their mother and sisters at four to four and a half weeks old to prevent them impregnating the does.
Females (does)
Female mice are known as does. They have ten nipples that they use to feed their litter until it is fully weaned at around four weeks. The nipples can be seen when a doe is nursing (at other times they are usually covered reasonably well by the belly fur) and are a good way to identify female mice since males do not have nipples. Nipples are most visible in young mice or in does who have had a litter. If the nipples are not obvious then you must rely on checking the mouse’s genitals alone to sex it. A female mouse's vagina is close to its anus, with little space in between the two.
Males (bucks)
Male mice are called bucks. They do not have nipples, but just because you cannot see a mouse’s nipples does not mean they are not there. If a buck is old enough to leave its mother (four weeks or older) then it should have fairly obvious testicles. Mice have large testicles in comparison to their body size, which will ‘drop’ as the mouse matures into adolescence.
Mice can retract their testicles into their body, so they may be there even though they are not totally obvious. If you are unsure there are several ways to deal with this. A simple way is to give the mouse a high sided food bowl to eat from and watch it perch on the side – if it has testicles they should drop at this point for you to observe. Alternatively, when you lift the mouse to inspect underneath, you may still be able to see the slightly baggy scrotum even if the mouse is retracting its testicles. This is more obvious in older mice who are fully developed. You should also check the anogenital distance. The distance between the anus and the genitals of a male mouse is larger than it is in a female mouse. If you compare the two you will see that while the female’s anus and vagina appear almost joined, the male’s penis is spaced quite far apart from the anus.
Babies
Lots of beginners find it difficult to sex baby mice, but all you need is a bit of practice - and ideally someone to show you how. Below are some photos of pinkies and furred babies that may help.
Females (does)
Female mice are known as does. They have ten nipples that they use to feed their litter until it is fully weaned at around four weeks. The nipples can be seen when a doe is nursing (at other times they are usually covered reasonably well by the belly fur) and are a good way to identify female mice since males do not have nipples. Nipples are most visible in young mice or in does who have had a litter. If the nipples are not obvious then you must rely on checking the mouse’s genitals alone to sex it. A female mouse's vagina is close to its anus, with little space in between the two.
Males (bucks)
Male mice are called bucks. They do not have nipples, but just because you cannot see a mouse’s nipples does not mean they are not there. If a buck is old enough to leave its mother (four weeks or older) then it should have fairly obvious testicles. Mice have large testicles in comparison to their body size, which will ‘drop’ as the mouse matures into adolescence.
Mice can retract their testicles into their body, so they may be there even though they are not totally obvious. If you are unsure there are several ways to deal with this. A simple way is to give the mouse a high sided food bowl to eat from and watch it perch on the side – if it has testicles they should drop at this point for you to observe. Alternatively, when you lift the mouse to inspect underneath, you may still be able to see the slightly baggy scrotum even if the mouse is retracting its testicles. This is more obvious in older mice who are fully developed. You should also check the anogenital distance. The distance between the anus and the genitals of a male mouse is larger than it is in a female mouse. If you compare the two you will see that while the female’s anus and vagina appear almost joined, the male’s penis is spaced quite far apart from the anus.
Babies
Lots of beginners find it difficult to sex baby mice, but all you need is a bit of practice - and ideally someone to show you how. Below are some photos of pinkies and furred babies that may help.
Young doe
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11-day old doe
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Young buck
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11-day old buck
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