How Can I Tell What Sex My Mouse Is?
Photos by Cait McKeown
There is a noticeable difference between a male (= buck) and female (= doe) mouse. A buck is usually slightly larger and its urine has a stronger smell. The easiest way to sex mice when you are a beginner is by direct comparison - the distance between the anus and genitals is greater in the male. Mice can be sexed from birth in this way once you've had a bit of practice - so there's no excuse for pet stores saying they 'can't guarantee it's the right sex'. If they can't guarantee the sex, they don't know enough about mice to be selling them.
When you buy a pair of mice, before you leave the pet shop gently lift their tails and compare their genitals. Look at the mice from the side as well as straight on. If the mice are the same sex they should look exactly the same. If you're not sure, try a magnifying glass or take them to a vet or humane society and ask them to check. Male mice can retract their testicles, but you can still see that the gap between the anus and the external genitalia is larger in the male.
Incidentally, if you are trying to buy a mixed-sex pair of mice, please think about what you will do with the countless babies that may result before you go ahead.
Some good photos comparing male and female mouse genitals are available on the Internet at the Yahoo Group Valerie’s Mice Paradise: http://groups.yahoo.com/group/valeriesmiceparadise. Look in the ‘Photos’ section on the left-hand side of the page, at the album entitled ‘Cait’s sexing mice album’. Some good line drawings accompany guidance on sexing mice at Reite’s Rodent Roadshow at http://members.aol.com/Reite/MouseGuide.html.
If the mouse is old enough to leave its mother and it is male, it will have testicles. These can be drawn up into the body but if you lift the tail slightly and look underneath you'll still see the slightly baggy scrotum (lovely!). The testicles will not remain drawn up inside the body for any length of time. Mice have very large testicles relative to their body size - an adult male's testicles are each about the size of a small peanut (minus the shell). Try putting the mouse's food into a high-sided bowl. The mouse will perch on the side of the bowl to eat. If it is a boy, its testicles will soon drop down and dangle for all to see ;-) Only female mice have prominent nipples, so it might be worth examining the mouse's tummy. Nipples are visible in tiny babies, but once hair grows they can be hard to spot unless the mouse has reared a litter.
How to Sex Mice
Sexing Female Mice:
Determination of Sex - The Scientific Way (Jackson
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