11/12/2025
There is still lots of misunderstanding in the rat community about rats getting pregnant through the bars, it’s something I explained on a local page recently so this well worded post came at a perfect time.
Females need to be in Lordosis for mating to take place and if anyone’s seen mating in progress they know females can also be quite difficult to catch!
Pregnancy through cage bars simply cannot happen.
A significant amount of posts asking if it is possible is related to wildie x domestic, while Rattus Norvegicus are both wild and our pet species and can have successful pregnancies, Rattus Rattus who are the more common suburban rats (roof rats/black rats) are a different species and even if a mating did happen cross species, it cannot come to term.
It’s far more likely that wildies have snuck into the cage or domestics have snuck out if people end up with pregnant ladies and same goes for domestic x domestic “through the cage bars” pregnancies so it’s a good reminder to double check your cages and make sure there’s no sneaky gaps or bars can be pushed/bases to be slid past or weak latches that can be opened by little grabby hands.
~..:Educational Post:..~
Let's talk about breeding/mating through bars and rats!
This is a common thing discussed in the rat community, but it stems from a misunderstanding of rat anatomy, and determination.
Firstly NO rats cannot mate through bars. Their anatomy doesn't allow for this, and it's studied! Male rats "bits" are too short to reach properly. But even if this weren't the case there's another issue!
The female rat has to be touched in two places to be properly stimulated for pregnancy. One internally and one externally. This simply CANNOT happen through barred cages. She will then go into a special position called "Lordosis".
(see first picture)
https://www.researchgate.net/figure/Rat-mating-behavior-The-female-is-displaying-the-so-called-lordosis-position-during_fig4_315877080
This study is a lot of "sciencey" terms, discussing how chemicals in the brain affect lordosis, and really interesting too:
https://pmc.ncbi.nlm.nih.gov/articles/PMC4166118/
If anyone has access to this study and can share it I would love to read it in full vs just the summary:
https://www.sciencedirect.com/science/chapter/bookseries/abs/pii/S0079612308644398
So what about those who claim it's happened to them? Or that they know a pet owner/breeder it has happened to?
Honestly I don't believe they are lying. Clearly they believe that is what has happened. I just think they lack knowledge and understanding.
There's a few things that CAN happen that make much more logical sense.
- Rats can put a embryo, or multiple "on pause". This is common in many small animals not just rats. Basically the female holds fertilized embryo's till later. Typically a few weeks to a month after the first litter is born.
Then she will have a second one. Usually smaller, but not always.
If cages are right up against each other it's easy for those who don't know better to think the got pregnant through the bars.
But as we all ready stated this isn't possible scientifically.
- Rats were put together by someone else, either on purpose or by accident. In some cases we get busy and breeders forget who is in what cage, or a rat is missed during playtime.
Sometimes children or a caregiver who is trying to help, put rats in the wrong cage or play area.
Sometimes a curious human will put the rats together on purpose to "see what happens".
If the breeder isn't informed it can be easy to assume tehy bred through the bars.
- if the cages for the males or females have bar spacing of 1 inch or larger rats CAN squeeze through. Female rats in heat are determined to go find a buck. Mine for example, will climb out of the cage and try to "go find a boyfriend" every time. (However I have precautions in place to prevent this which I will talk about in a sec.)
it's also not uncommon in these situations for the rats to go visiting and then put themselves BACK where they actually belong. Leaving the caregiver none the wiser.
*To prevent this, wrap all cages that have 1 inch or larger bar spacing in 1/2 inch hardware cloth. Only open the door to one cage at a time. ALWAYS. No matter how far across the room the cages are or how high up off the floor. Rats are quite agile when they are determined.
I also try to keep my boy cages in a separate stack or shelf than my girls, but this isn't always possible.
And I supervise my kids when they interact even though they are 10 and 14. accidents can happen and they aren't ultimately responsible for my rats. I am. *
There are of course some instances where one of the above happened and the owner feels ashamed about it, so they may lie and say they bred through the bars to absolve them of responsibility.
To this I say, do not feel ashamed! You likely didn't know, or it was an honest mistake. While in a perfect world mistakes wouldn't happen, we are human in a fallen world that is constantly degrading. The judgement from others is not something to worry about. Instead make steps to prevent these things in the future and do better immediately!
Shame towards other breeders for making honest mistakes needs to stop.
And also doubling down on false and impossible info needs to stop. It's hard to be wrong. Been there myself. But if we never take the time to absorb new info we can't grow as a person or breeder.
