Questions and Answers

PREGNANT MICE

Do you have a question you would like answered about your little mice and rats.

Question   Jan,A couple of weeks ago we purchased two curly haired mice.  We have noticed our little blackmouse has gotten rather tubby, we think she could be pregnant, she no longerruns on the wheel and only seems to break down toilet rolls and use them forextra bedding and moves the timber shavings bits into the house area. 1. What do we do?2. How long before if she is pregnant will she have her babies?3. How many could she have?4. How long do the babies stay with her?5. How do we tell if they are male or female? Look forward to your reply. 

Helen.

If your mouse looks like it?s rear end is swollen out of proportion to the rest of her in a very short time, then yes, she would be pregnant.  The mouse will have a waxy plug in its vagina if it has just become pregnant.  This will disappear and she will also develop nipple spots underneath if she has never been pregnant before.   The pregnancy tends to show around the end of the second week.  The making of a nest can be another sign.  A mouse will be pregnant for 18 to 21 days and will have as many as 20 babies, or as little as 4 the first time and it is advisable not to touch them for the first 5 days.  If the animal is unsure of you or has not known you long enough they may be nervous of anyone coming too close to the babies and may eat them  (animals will eat their young if they feel threatened).  Another reason they may eat them is if they are unwell and unable to feed them and sometimes she can mistake them for the placenta.  A mouse will not generally eat their babies after the five-day period.  The mother does not require any help from you and will manage on her own.  However, if she is extremely young (at 5 weeks of age), a first pregnancy can be fraught with danger and if you have an older female to put in with her (in the early stages of pregnancy?not the later stages) then she will help with the birthing.

She will feed her young for 3 weeks until they are weaned and able to eat on their own.  They should be removed from the mothers care in the fourth week.  Any longer and the females could become pregnant.  If there is a male in the cage when the babies are born the female will most likely be impregnated within a 24-hour period.  If you are leaving the male in the cage (and it is safe to do so if they are his babies) then he will make a good father.

The pictures below show the difference between male and female mice.  Before they get fur (approx 10 days old) you can see any nipple marks on the underbelly, however, this is not evident at 4 weeks of age as the fur covers it and sometimes it is nearly impossible to tell even at that age.  The simplest way is to check one against the other and the one with the shortest distances are probably female.  Another way to check is by noting if there is a slight purple colouring near the anus.  This usually indicates the scrotum of the male.  Nearly always the male will push out his scrotum to reveal a raised lump.

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