Mouse wont accept new mouse

Question
one of my female mice who i have had for a while now keeps attacking my newest female mouse. however she has accepted other females with some difficulty but she had never attacked them just to attack them. normally its small little fights but this time she is practically hunting down the new mouse. will this problem be resolved or is it too dangerous to introduce this mouse. also i am planning on breeding the new mouse with my male and i want to keep some of the babies should i be worried that the ones i keep will also be in danger. and is there ne way to help them get along.

Answer
Dear Sara,

First, because you have had experience introducing  mice, you probably know what is OK. Basically, chasing and squeaking is OK as long as:

1. there is no blood.
2. no one is kept away from the wheel, food, water, or nest.
3. no one is depressed and lethargic.
4. the chasing and squeaking is nonstop rather than sporadic.

I have had a situation where one mouse felt she needed to show who was boss quite frequently. The chasing and squeaking went on every night for well over a month. I was starting to become worried that it would never stop, but none of the above conditions were broken, and everyone seemed OK. Eventually it stopped.

So now I am assuming you do have an untenable situation.

Most females do get along, but sometimes it just doesn't work. Whether the problem is that the new mouse refuses to accept domination, or that the older one somehow perceives in her an easy target, I don't know. And sometimes it just doesn't work no matter what. But let's try one thing first.

Clean the cage. Take the aggressive mouse out and give her her own cage quite close by. Keep her out for three days. Then try again. Sometimes mice have a rather complicated equilibrium in a group and this may interrupt it.

If this doesn't work, you may need to do some separating. Don't have one mouse alone. Keep the cages close.

Don't worry about breeding unless the mouse shows symptoms of being different when she is not under the domination of the older mouse. Observe her when the other mouse is in her own cage, and if she appears normal she can breed. You should wait a month first to make sure she feels comfortable in her new surroundings with her new friends.

Have fun with your little mice!

squeaks n giggles,

Natasha