Inbreeding in feeder rodents

Continuing the discussion from Breeding siblings together?:


Hello! By no means do I have any real experience in the subject, but curious to the fact that ASFs do not allow new mates into the colony from my understanding, unless it is one of the offspring raise up with the original colony. Are they like this in the wild as well? I would think that inbreeding with ASFs is going to be more issue because it is so hard to introduce new blood.


Yeah kinda different topic but you need to inbreed ASFs.

Introducing new blood to a “line” can undo all the work someone has done with a pet quality line and bring back aggression/biting behavior, young eating, the extreme chewing, etc.

You’re way better off to find a line someone has been working with already and keep going with it than to “start over.”


Understand that for captive bred. But do they continue to inbred in the wild? Wasn’t trying to get off subject considering people were discussing rats and mice, and ASF would fall into that category.

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I’d assume so pretty heavily. Some probably get pushed out of their colonies and try and find new ones but I’m sure most of those get eaten


Since breeders generally last for about a year or so before needing retirement I’m not sure how many years/generations down the line it would be before you’d “need” to splash some new blood in because the very basics still hold true genetically

But I’m guessing it’s quite awhile. Many of the “pet quality” breeders I follow have been going for years and have no signs of issues that I can tell

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Here is a paper I found on the social behaviour in ASFs

Interesting to note that in the wild they seem rather non-aggressive but in captivity they develop behaviour. At a guess, the lack of spacial constraints probably induces the aggressive behaviour


As far as ASF go…when I pull the weaned young (doesn’t matter from what colony) they all go in a grow out…as they grow out, most get fed off…by the time I they are sexually mature I’ve left 3 to 4 males with 7 to 10 females (usually a 3.7) and thats the new breeding colony with a good mix of bloodlines…im also always on the hunt for breeders who are willing to sell males and females to add new blood to the room

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Before I stopped breeding rodents, i was easily into 15+ generations of inbreeding rats/mice/asf. They only got stronger as I selectively bred, never saw a reason to ruin it

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As @chesterhf points out in another thread, nothing gets stronger through inbreeding. The traits you wanted got passed on easier, but you could do it without inbreeding as well. Then again, if you are breeding things just for snake food, you don’t have to worry too much on if they live long.

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My biggest gripe with this argument, is “how do you know they only got stronger?”. Do you have a control group of outbred strains that you’re comparing to? What is the criteria here? Are you documenting size of each litter, weight of each mouse at weaning (21days), reproductive lifespan, % of mice that need to be culled for health reasons, body condition, male/female fertility and and if any of these things gradually changed or decreased with over 15+ generations would you know? Or is it just that these mice/rats are producing enough offspring to meet your needs and seem to be healthy enough.

People always jump to malformations like extra limbs or deformities as the outcome of severe inbreeding, and while they can be, in reality it’s much more likely to be subtle things like failure to thrive, higher rates of cancer, decreased fertility and reduced immune function. The latter would be one of my large concerns, as exposure to a pathogen can easily wipe out an entire inbred colony because their immune function is severely decreased.


This is totally incorrect you have to use some of the mice or rats as breeders so of course you worry if they live.

And how do you suggest doing this without inbreeding? If you never bred rodents or don’t have a backround in genetics what are you basing your statements on?


I mean, you just replace the breeders you have with new ones. They don’t take long to grow after all. Just found a large female mouse in my feeder bag the other day, so it isn’t like they can’t be replaced.

You do it the same way you breed quality animals of all kinds (dogs, rodents, snakes, lizards, horses, birds, fish). You find someone that has stock that isn’t inbred, that has the traits you want, and add it to your stock. Rinse and repeat and just keep adding more new blood that has good genetics. You don’t have to have experience with something or a degree to have done research on how things work (the glories of not being able to complete college because money). Breeding for traits without heavily inbreeding isn’t that hard, just takes more time and money. Things like large litter size isn’t a one-off occurrence that will be hard to find in most mammals. If you want, since @chesterhf is a geneticist, maybe she can explain how to do it so you trust her word. If @t_h_wyman has the time (it is fine if you don’t) he could chime in too.

Presence of spacial constraints**

Interesting. I will have to read up on this, thanks for the share!

Again, rodents are built different.

Would I use the word “stronger?” No because of the lack of control group testing etc but they’re able to withstand many generations of inbreeding without negative visible effects.


You could also try introducing them like how you do some birds. Let them get used to each others presence first by keeping em in separate cages near each other, then introduce them in a spacious environment. Maybe one could also dedicate a full room to them monitor lizard style and see if they get along better.

We aren’t just talking about visible effects though. Most inbreeding effects aren’t visible, just the most shocking and upsetting. And the hardest to hide or ignore.

I shall quote some of what our geneticist that deals with heavily inbred lab mice on a regular so she doesn’t have to repeat herself. I also recommend playing a game called Niche if you wanna see an easy to understand example of how genetics work with inbreeding.

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Which is why I said visible effects.

There’s no point in us saying over and over rodents are built differently if you don’t want to believe it don’t believe it. You’re responsible for your own animals. As long as your colonies are doing well then keep up whatever you’re doing.


If a geneticist is also saying that rodents aren’t built different (because they aren’t). Then why would you not believe the person that has gone to college, graduated, and gets paid to know these things? @chesterhf has actual lab mice, and access to a ton of info, yet you seem to not wish to believe what she says. Whatever makes it easier to sleep at night I suppose. I can’t personally breed rodents due to my asthma, but I definitely wouldn’t want a sub par colony if I had the choice.

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