Sexing mice

So as a new, unexperienced and curious mice breeder I've been looking a bit extra on my mices genitalia to try to spot the one male in each cage. I actually find this very hard (maybe I'm stupid and don't know what I should look for).

How do you determin the sex of the mouse?

Is there a fool proof way?

Thanks
-D

Most of the time I check their belly. If it's a girl and an adult you should be able to see her last nipples even if she's not prego. My wife is better at picking out the males than I am.

http://research.uiowa.edu/animal/mp7.jpg

i saw ralph davis in one of his videos you give them a lil squeeze and the balls will pop up it sounds `cruel but its not you dont do it hard just squeeze a lil on their belly and its very effective.

I do have to wonder how you know if you have one male in each group if you can't sex them... :P

First step in sexing mice: do not be fooled by something that might look like a mouse sized penis. I don't know what this is called, but both males and females have it. I'll just refer to it as the genitals. It does seem to be larger, at least on average, in males, but I don't find that the easiest way of sexing my mice.

Adult mice are easy to sex once you know what you are looking for. What you should look for is the scrotum; males have a fairly large scrotum for their body size. If you pick them up by their tail, they'll pull the testicles in, but it is still possible to see the little folds of skin of the empty scrotum. However, it is much nicer to just let them set on your hand for a moment, and then it should be very easy to recognize the males. Also, if you compare a male to a female, you will notice there is more distance between the anus and the genitals on males than on females. See the picture Clear posted.

With younger mice, it is more difficult, but not impossible. The boys have not had their testicles descend yet, so you have to go by the distance between the anus and genitals. Remember it will be larger on males. Supposedly, once you have some experience, you will be able to sex mice as soon as they are born using this method. I'm not that good yet, but by the time they are getting close to weaning, even before their scrotum becomes evident, I can accurately sex almost all of my young mice with this method. Occasionally, one seems to have a medium distance, but when I check again in a few more days it will be more obvious.

Females have a 'slit' and visible teates. Malse have huge 'balls'. Males also grow faster than girls.

Well to be perfectly honest I don't know. :) I bought all the mice from a woman who seemed very experienced in breeding mice and rats and told her what I wanted and she put them in 3 different boxes in the colonies they were intended to be permanently, so I guess I just trust her. :rolleyes:

I've seen the same vid from RDR, however that's rats and it feels like it's easier "popping" rats than mice thanks to the size difference. I'll give it a gentle go at next cleaning time and then check genitalia distance etc. My biggest problem is, I can't pick one up, check him and then put him/her back in and take another one. Simply because they are all labb mice and are all white with red eyes, there is absolutley no way to tell a difference between them so I might just pick the first one up 3 times or something. :D

Cleaning day is tomorrow, I'll update after that. Thanks for all the replies.

Once you figure out which are the males, you can put a dot of food coloring on their back to identify them. I've done that a few times for various reasons and it works well as long as you renew it regularly.