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Pregnant mouse   QUESTION: Well i bought two mice months ago but the petshop missexed them and i ended up with a litter of mice well now i think that the males have mated with their sister well i know she's pregnant but i don't know the father i'm really worried this was not planned i would never ever inbreed mice that and i'm worried about her health and life she's about 8 weeks old and mated at 5 weeks i'm guessing that and her mother seems pregnant again but i'm not sure she has really obvious nipples and a pot belly that comes out a bit more than usual they have both been hoarding food and ripping up their bedding and they spend most of their time in their nest also if they are both going to be nursing is it ok for them to share a cage? i'm worried about them stealing babies and tug o war happening with them. they have been really close so i don't really know if i should separate them. i will attatch a photo i also wanted to find out when to expect the babies because where i am now it's really chilly outside so a brought them inside i'm going to try and sound proof my room a bit because my nanna is always yelling really loudly would this trigger canabalism? well the white one (Malt) is the pregnant one that i am certain is pregnant but i need to know when to prepare for birth.

ANSWER: Dear Gala,

You have a common situation. Pet store employees sometimes have no idea how to sex mice. In many cases, however, the pet store will take back the babies and the male mouse, because it is their mistake. You might want to find out.

It is fine for two mice to share a nest with their litters. Actually it's very convenient for them. One mouse can run around in the wheel etc., while the other keeps the babies warm. It's also fine for mice to inbreed for a generation or two. So it doesn't matter who the father is.

Your most important worry right now is getting the sexes separated. As you have found out, female mice can be sexually mature at 4 1/2 weeks. Thus you will need to figure  out the sexes by 4 weeks, when you separate them. Males usually aren't mature till 6 weeks, but there might be one precocious one.

There are three ways to tell males from females.  The first thing you do is check the babies' bellies at about 5 days. They will have little enough fur that you ought to be able to tell which ones have nipples. Male mice do not have nipples. That way you will know how many males and females there are. If they have markings, make notes with pictures to remember which is which. If they are all white that won't work of course.

The second way you can do anytime, and that's to compare the distance between the genitals and the anus. Both girl and boy mice have the same protrusion that looks like a penis. Boys have more space between that and their anus.

The third way only works when they are becoming sexually mature. Mature male mice have very visible testicles. They protrude under the base of their tail and some people mistake them for a butt! Mice are confusing!

This guide should be helpful in determining the sex of your mice:

http://www.thefunmouse.com/info/sexing.cfm

However, just separating them will not be the end of your problems. The thing is, when male mice get older they fight. And they will kill each other. Male mice almost always have to live alone. So now you need one cage per male mouse. You will probably want to find homes for them instead, and I suggest you start trying now.

It's good to bring them inside and try to keep them in a quiet place. You do have to worry a bit about mice getting upset and eating the babies because they don't think it is a safe place to raise babies. However, you can only do the best you can, and hope.

As for how pregnant that mouse is, it's hard to tell. Because mice can have anywhere from one to twenty-two babies, she could be any size. I would just assume a pregnant mouse is going to have babies 3 weeks after she is sexually mature and was with a male. But why did they become pregnant so early? The father isn't still in the cage, is he? You're going to have hundreds of babies if you don't separate everybody. Mouse populations simply explode before you can blink.

I hope you can resolve your mouse problem. If you have any more questions, first check my archives, then write me back. Best of luck.

squeaks n giggles,

Natasha







---------- FOLLOW-UP ----------

QUESTION: Thank you very helpful i had already separated these mice and they are doing well, now my pregnant mouse that i wondered when she was going to give birth is in labour now and i'm worried because she was a runt that she wont cope well i was scared when i saw something happen i was wondering if it was normal i saw a large amount of bodily fluid come flowing out of her when she was breathing heavy and pushing i figured it was like her water breaking is this normal? i could see the babies inside her being pushed but don't worry i'm not watching her now i left my fish tank light on and turned everything else off exept the tv in my nanna's room is it ok to have it on? well i also found out that her mother is also pregnant i'm hoping they will help each other with the litters also when can i take a small peek at them? i will be away for the Christmas holidays so i'm worried that they need my help while i'm away so what do i do now? thanks for the great advice by the way it really helped

Answer
Dear Gaia,

To tell the truth, I always left my mice alone to give birth so I haven't witnessed the breaking of the water. I never had an issue; mice are pretty good at being pregnant and having babies. That doesn't mean nothing can go wrong. However, the difficulties that I am aware of are usually that the babies become stuck, which would be because it was too dry, so being wet is probably a good thing. I'm sorry I can't give you a real answer on that one, but very likely everything is OK.

Yeah it's OK to have the TV on in the other room. Just no unusual or sudden noises. As I said, the females will help each other.

Because she is so young, I would not want to disturb her and try to see the babies right away. Wait at least 4 days. Take her out of the cage first and set her down somewhere familiar or have someone hold her before you disturb the nest. They'll be OK during your vacation, assuming it isn't a very long one. You should begin handling the babies on day 7 to make sure you socialize them successfully.

One last hint: Give the mothers some extra protein such as some cheese or cooked egg to help them out.

Have fun with the babies : )

squeaks,
Natasha