American Fancy Rat & Mouse Association

This article is from the Summer I 1998 AFRMA Rat & Mouse Tales news-magazine.

Breeding & Stuff

Too Many Babies?; Mom Mice Attacking Babies

By Nichole Royer

Too Many Babies?

Katie Morrison, Scottsville NY
Q I have two rats: a girl named Ronda and a boy named Rizzo. They are both Siamese, and Ronda is older than Rizzo. They are intelligent, especially Rizzo, who is also more active.

Ronda & Rizzo

Yesterday Ronda gave birth to at least twenty pups — or more!

I read in the book I purchased last week that 20 or more pups are rare, and this is Ronda’s first litter too! The book is called: Guide to Owning a Rat by Susan Fox.

A Yes, 20 babies is fairly rare, though not unheard of. Unfortunately, this many babies can place a great burden on the mother rat. Some of the babies could also do very poorly, or even die, because they can’t get enough milk and are too small and weak to compete with the other babies.

There are several things you can do to make things easier on her. In a case like this it becomes especially important to make sure your rat has an adequate and nutritious diet. The best is a good quality lab block (as much as she wants), supplemented with fresh fruits, vegetables, pasta, whole wheat bread, and a small amount of high-quality dog food. Also make sure that her cage is large enough, kept scrupulously clean, and that she has a place where she can get away from the babies once they start crawling around.

If you discover that some of your babies begin to do poorly, are very small, constantly cry for food, or the mother begins rejecting or ignoring some of them, you have several options.

If you can find another female rat who has a small litter of babies who are about the same age, it is a simple matter to foster some of the large litter to her. Take the foster mom out of her cage, rub the babies with some soiled bedding, then put them in with the smaller litter. Give them about 10 minutes to settle down, then put mom back in. Most females will closely examine the new babies, then accept them happily.

If no foster mother is available another option would be to attempt to bottle feed some of the baby rats. This has to be done every two hours round the clock, and is sometimes successful, sometimes not.

A third option would be to cull some of the litter. If the smallest and weakest are humanely put down, the rest will have much more access to enough food. The mother rat will also be much calmer and less stressed.

Finally, you can do nothing. Often the smallest do not survive, or they remain very small throughout their lives. Most of the litter will probably do okay, though some may have trouble putting on weight and may do poorly.

Mom Mice Attacking Babies

Lynn Lehman. Racine, WI
Q About two weeks ago, I purchased six more female mice, and a week later one of them had five babies! They are now doing very well and all look exactly like their mother. (She is white with large patches of a dark tan color). I have come to call her “Goofy” as she is very silly, jumping around like a little monkey and is overly friendly!

Anyway, there was a problem with one of the other females always picking up the babies and throwing them around, but she never really hurt them until yesterday.

I came home from work just in time to save one from being chewed on and tossed all around! She would not let go no matter how hard I tried to make her drop it, so I finally had to pick her up by the tail and she finally let go. The little one is pretty badly bruised and raw, but, thank goodness, will be just fine.

Why would this other mouse act so vicious? (She is now all by herself). I’m pretty sure she is also going to give birth any day now, could it be she is jealous of the other babies? Now I am very afraid that she will also attack her own babies when they arrive. Is it possible to foster her babies to Goofy if this female attacks them?

A Strangely enough, this is a fairly common occurrence in mice. If two pregnant females are housed together and one gives birth first, it’s not unusual for the other to act aggressively toward the babies.

Actually, you were very lucky. Most mice that do this simply kill the whole litter. We are not sure why this happens, but I suspect it is a survival characteristic left over from our critter’s days as wild mice. It probably has something to do with the mouse eliminating her litter’s competition. The older litter, being bigger and stronger, would naturally out-compete the younger litter.

It is for this reason that many breeders will separate pregnant females into their own cages to give birth and raise their litters. Others let their females raise their babies together, and have no problems. American pet shop mice seem to be more prone to this behavior than English and English-cross mice.

Chances are that this mouse will not attack her own babies; however, there is always that possibility. It is often difficult to get a mother mouse to accept and foster new babies, particularly if her babies are much older and larger. Also, the older babies tend to out-compete the younger ones for food.

The one time female mice do seem to easily accept another mouse’s litter is when both are housed in a communal cage. When a communal nest is formed, a female mouse will feed all the babies in the nest, even if some are much younger. If one of the females is removed from the cage, the other will continue nursing all of the babies. *

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Updated February 14, 2015