Baby mouse not growing?

Question

Three weeks ago we got two new baby mice after our daughter's old mouse passed away.

The babies were about three - four weeks old albino "feeder" mice. They are both females from the same litter.

When we brought them home, we realized that one was a little smaller than the other but, not such a big deal. Now three weeks later, the size difference is gigantic! The larger one is the size of an ordinary adult mouse but, the smaller one hasn't grown at all. She is the exact same size as she was three weeks ago. The big one is easily two or three times larger than the little one.

Both of them seem healthy (besides the lack of growing), active, and happy. They get along just fine. I often see the bigger sister grooming the little one. And the little one does eat often and drink, so no problems being deprived of food and water.

Does anyone have an idea why her growth seems stunted? Has anyone had a similar situation? Thanks!

Answer 1

As long as both mice are eating, drinking, and pooping/peeing normally chances are they are fine.  As long as the mouse isn't lethargic or anything, chances are the smaller mouse is just a slow grower or perhaps the runt.  I wouldn't worry about it.  The mouse will probably start growing at his own time, just as human children develop at different rates.

If something does change regarding their activities, contact a vet for further advice.

Hope that helps!

Answer 2

I've had the same situation with my fancy mice. The 2 female mice were from the same litter and they were very young. About a month later, the small one still stayed small and the large one was about 4 times the size of the little one and they are both pretty active. I've had them for about a year and they are still happy as ever.  

Answer 3

They are probally fine but one thing is that they won't live as long as fancy mice

Answer 4

Mice can vary in size. The smallest (adult) mouse I had was about 27 g, and the largest was around 60g - so, as you can see, it's a huge difference (over the years, I've had close to 30 mice, and the average weight was probably 30-35 g). There's no way to tell if the mice you got are littermates - these mice are bred in large quantities, and they can come from different parents. If she's acting normal, and is eating/drinking, I would just let her be. Maybe she's on the small-ish side, could be a runt of the litter. Look at the bright side - with the size difference, you'll be able to tell them apart! :)