American Fancy Rat & Mouse Association

This article is from the Winter 2000 AFRMA Rat & Mouse Tales news-magazine.

Colors & Coats

Making Dumbo Rats; Inbreeding; Making Black Self Rats

By Nichole Royer

Making Dumbo Rats

Jenn, e-mail
Q How would I go about getting a litter of Dumbo rats? Right now I have a Capped female and I would like to get some Dumbos from her, any color Dumbos. I am looking for a Dumbo male. If I bred a Dumbo male to my female, how would I get Dumbo rats?

A Dumbo rats are very popular and, fortunately, fairly easy to breed. Unfortunately, your female is unlikely to have any Dumbo babies unless one of her parents were Dumbo.

Dumbo is a recessive trait. If you breed two Dumbos together, their entire litter will be Dumbos. If you breed a Dumbo to a normal rat who had one parent that was a Dumbo, about one-quarter of your litter will be Dumbo. If you breed a Dumbo rat to a normal rat who doesn’t have any Dumbo family members, your entire litter will be normal.

If you want to get Dumbos, you need to breed your female to a Dumbo male. Keep one of their daughters and breed her back to her father. About half of her litter should be Dumbo.


Todd Hanson, Middleton, WI
Q How long (how many generations) can you inbreed before the animals have problems, like waltzing mice? Can you introduce new blood later on down the line?

A Inbreeding in and of itself does NOT produce any sort of health problems. This includes waltzing. What inbreeding does is double up on whatever traits are present in a particular group of animals. Inbreeding is a valuable tool which should be used by experienced breeders working towards a particular goal. Used willy nilly, it can, however, be very detrimental. The key to inbreeding is careful selection.

If you inbreed a group of animals who all have traits for poor temperaments and ill health (not to mention poor type/color/coats), you will produce babies who have these traits. These animals will have a tendency to strongly pass along these traits to their offspring (whether you inbreed or outcross). If these animals are inbred, you end up with an entire population of animals who only produce these unwanted traits.

On the other hand, if you inbreed and then eliminate animals with unwanted traits from your breeding population, you end up with a group of animals which strongly passes along the traits you want. Naturally, in any litter of babies you will end up with some good and some bad traits in each baby. It is up to the breeder to carefully choose the best to use to continue the line. Over time with careful selection, a breeder should be able to successfully eliminate most of the bad traits from their line and produce babies which consistently have the good traits they want. The good traits selected for will vary from breeder to breeder.

It is when a breeder discovers that their line of animals does not contain the good characteristic they want, that an outcross (breeding to an unrelated animal) is vital. In this case, the best thing a breeder can do is find another line of inbred animals that very consistently produces the good characteristics they want. Naturally, this new line will also have its share of faults (there is no such thing as a perfect animal); therefore, the trick is to pick a line that complements your own, not one that shares the same unwanted traits as yours. For instance, if you are producing a line of mice that consistently have beautiful big bold eyes and ears, but short tails, you would want to outcross to a line that has really nice tails and, hopefully, at least decent ears and eyes.

How many generations can you inbreed? Well, I have heard numbers like 100–500 generations and counting in the laboratories. Often, these are big beautiful healthy animals that show no signs of problems from their extensively inbred background. Keep in mind, however, that the laboratories will cull extensively, with any problems being eliminated. This kind of extensive inbreeding is not recommended for the fancier, and any type of inbreeding should be approached cautiously by novice breeders.

Making Black Self Rats

Karl D. Bailey, e-mail
Q My wife and I recently picked up a Self Black male with absolutely no white or light patches and were kind of wondering what colors or markings would be a good match to breed with him to maintain his color or lack of markings.

A Ideally, you would want to breed him to a good Self Black female. If none are available, then any other Self rat will do. If you specifically want to breed for Self Blacks, I would stick with the non-agouti colors—Black, Beige, Champagne, Blue, and Lilac would all work. If you don’t care about the color and just want Self rats, then any Self, Agouti or not, would be okay. Chances are fairly good that a breeding to an Agouti would produce some Blacks.

If you have no other Self rats, you can use this guy to produce them. If he is bred to Irish/English Irish or even Berkshire females, some of the resulting offspring should have no white on them. These Self babies can be kept and bred together (or back to dad) and they should produce litters of almost all Self babies.

Self Blacks are also the recommended outcross for Siamese (if you have them). Siamese bred to Black is unlikely to produce Siamese (babies will probably be all Black) but if the babies are bred together, you will get Siamese. Outcrossing Siamese to Black often improves the foot and point color on the Siamese. *

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Updated March 3, 2014