I'm not sure if my mouse (or maybe mice) is (are) pregnant. Help?

Question

I had three mice, that, when I bought them, two were supposedly males, and the other was a female. I've had them for almost a year now and nothing ever happened. Recently, about three weeks ago, I bought a mouse that was very blatently a male, which was different from the others. I didn't really notice anything different until about a week and a half ago, when I realized the three other mice stopped running on their wheel, which they did constantly, and they've been laying in corners of their cage all the time. I saw one of the mice was significantly larger in the stomache area so I moved her into a different cage to be alone. I gave her a house, food, and water, and she mostly just lays down in a corner of her cage, and she's very large. I don't know if she IS pregnant or not so it would be helpful if someone could help me out.

Answer 1

Sounds like you have 3 females and a male. All three could be pregnant but the one you say is large is most definately pregnant. She'll probably have her young after 3 weeks and she'll be able to fall pregnant again almost instantly so keep the male seperated from the females because constant breeding can severely lessen the life span of the female and her health will suffer. Also you could end up with a lot of mice, females can have 20 or so young every 6 weeks and the young can breed at 6 weeks of age. So definately keep the male away unless you want to be overrun. Good luck, hope this helps.

Answer 2

It's very probable. Learn to distinguish a male and female rodent by yourself, so that next time you get mice from uneducated and probably new pet store workers this won't happen.

Answer 3

Probably all three are pregnant. You don't need to seperate the girls, but the boy has got to go. They can get pregnant again as soon as they are done giving birth, and back to back pregnancies are very hard on their health. Male mice are quite obvious.

Answer 4

Typically, male mice can't share a cage with other male mice.  If you've introduced a new male to a group of males then they're going to fight pretty badly.  Do you see any scabbing or bite marks on anybody's tails?  It's likely the new male, who is younger and stronger, is bullying the other males so they don't get food and water and they may actually die.

Female mice should only be bred when they are between 3 months and 9 months old, so if you do have a pregnant one who is at least a year old, this is going to be very hard on her physically.  She'll need a lot of food, she'll need yogurt drops or something as a calcium supplement, and she will probably only have a couple of babies.  The babies may not make it, and she may be fairly weak for the rest of her life so you'll need to keep an eye on her.

It's a bad idea to keep a male in with females constantly, because they can get pregnant again the day they give birth and it wears them out, which makes them prone to parasites and respiratory illnesses and isn't good for the babies, either.  And your females (it does sound like you have 3 females and a new male) are all too old to breed safely, so they shouldn't be kept with a male at all.

It's likely that the large one is pregnant, definitely--gestation is about 20 days so 3 weeks is about right.  The only other possibility is either a tumor or a digestive blockage, and given the timing it's much more likely to be a pregnancy.  The other two he may not have gotten to right away, or it may not have "taken" right away, or perhaps since you introduced him to their cage (when breeding you normally put the female into the male's cage or she'll beat up on him) then it's possible they wouldn't allow it right away.  But it's likely you're going to get 3 litters of babies, and it's likely the babies and the moms may be a bit sickly, assuming the moms don't eat the babies outright because they're too depleted to nurse them adequately.

The male needs his own cage, in perpetuity, starting now.  And you need to start thinking about what you'll do with between 5 and 30 baby mice, depending on how this goes.