Sexing rats is usually quite simple. Males are most likely going to be quite obvious from an early age, as they have very large testicles that are hard to miss.
To begin look for nipples, only female rats have nipples. But never judge on lack of nipples alone. Often babies are fairly fuzzy and it can be almost impossible to find them!
Looking at their genital region, the male's genitals will be farther apart from the anus then the female. It is usually pretty easy to tell if you have both a male and a female to compare them to.
If they are around 4-5 weeks or older the boys should be rocking some fairly good sized testicles, making sexing them pretty easy.
As you can see from the pic above, the boy has quite the noticeable testicles. You can also see from the girl that she is slightly "poofy" down there. Sometimes people will confuse this for testicles. Some girls just are alittle bigger down there, sometimes they are about to poop. But it is still fairly different looking.
Both have a little nub. On the boy it is his penis sheath, the girl it is her urethra. On girls there will be a hole undernearth where the vagina is. There is also a line from the vagina to the anus.
If you are trying to ask for help on gender, take good clear pics in good lighting. It helps if you have someone to help you. I highly suggest taking pics holding the rats like I am in the pics. It often gives a good clear shot.
Yes sometimes boys can hold their balls up inside them. It really does not happen that often. And when it does, you will notice. It looks weird lol
There are sometimes some special rats who will be lacking testicles, born with just one testicle, or be hermaphrodites. This is all quite rare.
It is possible to sex rats from day one. Males will have a wider spacing between the genitals and anus, females it will be closer together. If you are comparing itty bitty babies, the easiest way is to just pick one baby up and then start to compare each baby to it. When you notice a difference it is really obvious which is which.
I sex all of my babies at 2 days old and have yet to be wrong. *knock on wood* lol
By the time you have adopted your rat at 5-6 weeks or later there should be a visible difference in the boys vs the girls as shown above.
Mating & Pregnancy
DO NOT PLACE RATS OF THE OPPOSITE SEX TOGETHER UNLESS THEY ARE FIXED!!!
Mixed genders should not ever have play dates. They should not be housed together not even just for a little while. They should not be kept together even if they are related.
Rats can mate in the blink of an eye. It can happen very fast. It only takes you being distracted or turning your head and boom babies. It is so irresponsible.
Rats can also mate at very young ages and it is not a good thing. Babies should not be having babies. It puts both mother and babies at risk.
Rats do not need to mate. It doesn't make their life complete. It is not an experience they need to have. It will not settle them down or make them healthier or any other such nonsense. Breeding your rats is not something that should be taken lightly. It should be done only with alot of research and knowledge going in. It should only be done with rats who are of the proper age, history and health.
Breeding is not cloning. You will not get a carbon copy of your rat. If you do not know their history/pedigree they could be carrying health issues and temperament issues even if they are healthy/sweet. Also many health/aggression issues may not show up until later in life, even past healthy breeding age. So you have no way of knowing what to expect. You could lose your rat from complications as well.
Is my rat pregnant?
This often gets asked alot when people have brought their new rat home from a pet store where they often missex and/or keep different sexes caged together.
Most rats tend to gain weight, sometimes quite a bit of weight, when they enter a new home. They may have alittle bit of a belly on them.
Pregnant belly vs fat belly is usually quite different. It will kindof look like they swallowed some ping pong balls and are sticking out more to their sides.
Also most rats will not really show at all until their last week of their pregnancy.
If you do not know, visit a vet and/or wait and see, a rat is pregnant between 19-23 days.
If taking pics to ask for advice, I suggest holding a treat above her head to make her stand up to reach for it.
Examples of some of my pregnant does the last week of their pregnancy.