How To Sex Rats
By Lucie Mann

I have produced this guide to help new rat owners learn how easy it is to sex rats. I hope that by looking at the information here you will never produce a litter unintentionally because of sexing rats incorrectly! A second opinion won't be needed: you will be able to tell what you have in a litter the day they are born. Yes, it is that easy!

Adult Rats
I will start by showing you adult rats. Once you know what you are looking for, you can then look down through the different ages until you are looking at newborns and sexing them correctly.

Let me be polite, and show you the face of our models before showing you their bottoms!

This is Greenmann's Dart Angus. He is a Topaz Dumbo, bred by myself. If any of you have rats with Dagmar's Dart Maul in the line, then you will have rats related to him. He has a very sweet temperament and put up with lots of prodding and poking from me to take these pictures.

And this is Greenmann's Erma Dart. She is another Topaz Dumbo bred by me, and she is Angus's girlfriend! The baby pictures are all of their first litter together. As well as being related to Dagmar's Dart Maul, she is also related to Efraim of Zonien.

The first two pictures show the side view of an adult buck. If you look you will see the testicles under the base of the tail. People often refer to rats' testicles as "furry cushions". From this view you can see why... bucks do sit on them, and the hotter the rat the more the testicles drop, in order to keep the sperm at the right temperature. If your buck rat is getting very hot you will see pink bits at the end, as they expose skin for better heat exchange.



The next picture shows the same view of an adult doe.

Note that she has nothing to sit on! 

Some does have slightly longer fur which can look like a small bump hanging down. But when comparing the pictures of bucks and does, I think you will see it is easy to see the difference from the side.

Next if you lay your rat on its back you will be able to see the genitalia. If your rat is not easy to handle and you have trouble laying it on its back you can gently lift the tail upwards, but it would be cruel for the rat to take its weight by the tail - all four legs need to stay on the ground. You will not get a good view, and I would recommend that you learn to restrain your rat firmly and kindly.


I have left one of the pictures unlabelled so you can see how it will look on your rat. The anus is at the very base of the tail, if you gently lift the testicles you will be able to see it.


This is an adult doe, as you can see the distance between the genitalia is very small. When you read descriptions on what to look for it will always talk about the distances between the openings.

Compare this to the pictures of the buck. You can also see clearly the position of the anus. This is the same on both bucks and does, but as the previous pictures show, the buck's anus can be hidden.

When a doe is in heat the vagina will be dilated, and can sometimes look a dark purple colour. Immediately after a doe has been mated you can see the sperm inside the vagina, sometimes this can take the form of a vaginal plug, where the sperm has become solid to help it stay put. It is more common to see this in mice.

Young kittens have a "closed" vagina, it will look as though it has no opening. It only opens when a doe becomes sexually receptive. It is important to remove all bucks in the litter before this point. Although I have known does to remain "closed " up to the age of nine weeks when housed with sibling bucks, it is highly recommend to remove the bucks at five weeks.


The kittens used in this page are from Angus and Erma's first litter.

These pictures were taken at ten days of age. This is a very easy stage to sex them, as all the bits are easy to see.



Compare the two side by side:


On these photos you can see the differences in the sexes. Note the bucks' testicles have already started to drop.

On all the pictures you can see the navel. It is in the centre of the stomach. This can be confused with nipples, but bucks do not have nipples and there is always more than one! See if you can see it on all the pictures. Luckily rats rarely have unbiblical hernias; I have only seen one in 15 years. When they do it does not appear to do any harm.

It is at this stage that you can sex the rats by taking each kitten in turn and making two piles, one of bucks and one of does, you can then compare them and make sure that each pile only contains one sex. Even if you still cannot work it out from these photos, you will at least know how many of each you have!

If you look closely at the doe in the pictures you will see the vagina is "closed", it will remain so until they are sexually receptive. Droppings at this age are still small and can appear yellowish in colour due to the doe's milk. As the doe still removes and eats them at this age, don't worry if while you have them out the nest one appears and does not fall away by itself, the doe will remove it when you put them back.

Newborn Kittens


Note how you can see through the skin.

As you can see even at one day old you can see that the bucks and does look very different. The testicles show as a slight bulge already. You can see the navel and the milk band on both sexes.

It can sometimes take up to a day for all the kittens to have a full milk band, it will come and go as the baby digests the food, so you will not always see a full belly on each kitten. You should, however, be able to see it at least once for each kitten during a 24 hour period. But please do not disturb the mother more than is needed. Most ratty mums are very good about you playing with their babies, but she will want to get on with feeding her babies without your help!

I sex my litters when they are born, with practice you will be able to do so with ease. But do re-check as the babies grow!

I do hope this guide has been a help. I will add more pictures on different things to look for and abnormalities, on these pages as soon as I can