Rats can breed in a matter of seconds so you should never let males and females play together unless you want babies. Rats can mate in a blink of an eye and have been known to mate right through cage bars, so if you let a male play over near the females cage, you could still end up with babies.
Rat Pregnancy
Rats are pregnant for 22 days and can give birth anywhere from a couple of days before or a few days after the 22nd day. Rats can give birth to anywhere between 5-20 babies with smaller little happening more often than a larger one. A pregnant rat’s stomach will gradually get bigger each week but will be the largest in the last week of pregnancy. A lot of owners won’t notice until this last week that they have a pregnant rat because that’s when she will gain the most weight.
Pregnant rats usually eat a little more frequently during the day, and should have fresh fruits and vegetables available in addition to their regular food. Pregnant and nursing mother’s do need a little extra protein in their diet which you can give them by supplementing their regular food with a little dry cat food that has protein in it.
Some pregnant rats will start to make their nest in the last week of pregnancy, you should make available some soft bedding, such as baby blankets for her. Pregnant rats are most comfortable making their nests and giving birth inside a house or box of some kind. A plastic igloo lined with a couple of small cotton baby blankets should be made available in the cage for the mother.
Some pregnant rats may become more aggressive as they get closer to the time of birth and after giving birth may not want to be touched or have you touch their babies. This will probably pass after the babies are up and crawling around on their own. It may be best to take away all ladders and ledges in a larger cage so the mother doesn’t fall or jump and injure herself or the babies, until after she has given birth and the babies are walking around steadily.
Giving Birth
As the mother rat starts to go into labor and give birth, you may want to stay and watch but if she feels nervous or threatened at all it could cause her not to relax and take longer to give birth which could cause complications for her in the long run. She may also reject her babies if she feels nervous or threatened.
As the babies are born she will use her hands and feet to help deliver the babies, chew through the umbilical cord, eat the after birth and lick each baby clean. Mother rats may eat any babies that are born dead, she thinks they are sick or if she feels threatened or nervous, which is why you should leave her alone while she is giving birth.
New Born Baby Care
Newborn baby rats will squeak continuously and this is often the first sign to many rat owners that their pregnant rats have given birth. Do not handle or take the babies away from mom the first night, let her feel safe and recover from giving birth. After the first day you can handle the babies if the mother will let you and doesn’t seem skittish. Be sure to always wash and dry your hands before touching the babies, touch the mother first and then touch the babies so they all smell the same so the mother doesn’t reject one for smelling different.
Newborns will be carried around the cage in the mother’s mouth by her teeth, she is not hurting them when she does this even though they will probably be squeaking. Newborns will squeak about everything. Newborn rats go through several grown stages very fast. They are called ‘pinkies’ when they are first born because they are all pink and have no hair or fur on them. As they get fur they are called ‘Fuzzies’ and then “Crawlers” for obvious reason.
Newborns should not be kept away from their mother for more than a few minutes at a time until they have fur and are crawling around on their own because they need their mother to keep them warm and feed them several times a day. Babies will have have a full coat of fur and open their eyes between 10-14 days old, this is when they will begin exploring their cage and surroundings. At 2 weeks old the babies will start eating the same foods the mother eats so make sure they can get to the food bowls and add a little extra fresh fruits and vegetables for them.
After the mother gives birth the cage may be messy and there may be blood stained bedding. Wait at least one day to try and spot clean the cage. Lure the mother away from the babies to another part of the cage with a treat and remove the soiled bedding from the cage and replace with new bedding. I would use the small cotton receiving blankets (baby blankets). When the babies are two weeks old you can clean the whole cage by taking the mother and babies out of the cage and place them in a box with some of the old bedding and then clean the cage. It’s best to keep a handful of old bedding and place it in the cleaned cage so they come back to a cleaned cage that has some familiar smells. It will be less stressful for the family.
Babies are usually weaned by 5 weeks of age and should be separated according to their sex if you don’t want more babies because they can and will breed at this time even with siblings.
Sources:
http://ratfanclub.org/repro.html
http://www.boardmanweb.com/rattery/ratbreeding.htm