breeding a wild caught brown rat to a normal breeder.

I wouldn't do it. The possibility of benefits, is outweighed by the known negatives.

Temperament is heritable. You don't want to bring in that feral nature into your domesticated animals.
One of the goals of breeding our own feeders is to have well tempered animals that aren't skittish or aggressive. It makes handling them easy and feeding them off relatively safe.

Inbreeding in rats is not an issue. It does not cause issues. Rats can go hundreds of generations without a problem if selected correctly.


The issues are already in your gene pool if you're having problems. Inbreeding uncovers what is hiding in your genetics.

Outcrossing and bringing 'new blood' masks issues. Line breeding brings those issues up to the surface. When those issues come up, select away from those individuals. It's easy to select those issues out of your gene pool to keep it clean.

There have been pure inbred lines that are several decades old with no issues. Problems that occur is a line specific issue, not an inbreeding issue.

Line breeding also keeps unwanted traits out of your lines and wanted traits in your line. By outcrossing, you risk bringing in unwanted traits and modifiers into your lines. Only outcross if necessary. Some outcrosses have made lines worse.

I wish more people understood that you don't need to bring in 'fresh blood' for nearly any reason with rodents. Unless the new rodent you're adding in has some genetic positive that will improve your lines size/temperament/litter size/etc then there's no reason to do it. I have had the same line of ASFs for 7-8 years. I've actually got some pretty cool coat dimorphism going on from it.

Also I just wanted to add that just because the wild rat want showing any outward symptoms, who knows what diseases it was carrying.

Temperament is also very important like everyone else said. My mom has a kitten from a feral cat that gave birth their barn. She's had it since it was weaned and it's the meanest cat I've ever seen.

Norway rats(wild) are extremely wild and that temperament would probably breed true. Also, you would want to consider that wild rats are predisposed to chewing, so keeping even the great great grand rats in tubs would probably lead to escapes. I had one trio of black domestic rats that were chewers and every baby they produced, even when outcrossed to other lines would chew tubs. I had to eventually cull the entire line all the way down.

I think the only reason to bring in outside blood is because you want some color/coat that is not in your lines. There's no issue with line breeding though. The best thing is to cull/keep for what YOU want. If you want super tame ratties, those are the ones you keep back as breeders. If you want huge litters, keep those back. Eventually you will end up with a colony that does everything you want it to do.

My colony never bit, was almost all very easy to pick up and handle, produced okay and did not chew tubs. I just in the last month eliminated all but the hairless because the summer heat makes them not produce well and I frankly was tired of caring for a huge colony but still being short on feeders. So come fall, I may bring in new females to restart the colony, or I may just keep back the best of the hairless lines.

Last year, a wild rat chewed through 2 pressure-treated 2x4's to gain access to the building with our rats. He then chewed out hole in the back of one tub. My rats have been selectively bred for generations and I put down every rat in that tub. It's not worth risking a great line by adding wild-type genes that were environmentally selected for aggression and other non-domestic traits.