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

By Nichole Royer

Todd Hanson, Middleton, WI
Q We are trying to start two pedigree lines, agouti and black. One mom is totally agouti and one is totally black. Out of their litters we picked one all-agouti female and two all-black females. These three were the only ones that were all one color. We have new litters, and I’m sure we have at least one male of each, agouti and black. When they are old enough, do we mate them back—agouti male to agouti female (mom) or to agouti female (sister), and then what? In rabbits, Rex is pure if all the babies are Rexes, but in mice it’s not all the same, is it? You’ll get a mouse, but it’s the color that makes it pure, isn’t it? Once we get three generations of all one color, do we have pedigreed stock? I’m in the dark on a lot of this, so your help would be greatly appreciated!

A This is a question asked fairly often. In rabbits, once you get three generations that produced all one color, you have pure stock.

In rats and mice, there is no such thing as purebred, with one exception. A purebred English mouse is a mouse that traces its lines straight back to England with no American blood introduced. You can’t create purebred English mice, you have to either import them yourself or buy them from someone who has.

Pedigreed rats and mice are simply animals that have a recorded family history. You can have pedigreed rats and mice whose lines only go back one generation and then say unknown/from pet shop. You can also have pedigreed rats or mice who have lines that go back 10, 20, 30, or more generations. A pedigree is only a record of an animal’s background. Remember, a pedigree in no way guarantees quality of the animal.

There is a standard way to start a line of rats or mice, though it is by no means the only way. You start with a male and two females. Ideally, the females are not related to each other or closely related to the male. The females should compliment the male’s faults and each should excel in whatever points the other does not.

Standard procedure is to breed this male to each female. Keep the best male and female from each litter, breed the daughters back to their father and the sons back to their mother. Choose the best male/female pair from each branch and breed them together. This will give you two branches of the same line that excel in different areas and that complement each other.

This, however, is very rarely done. Needless to say, it involves breeding rather a large number of litters and keeping quite a few rats or mice.

What most people do is find the very best male they can and a female who complements his faults. They breed the female to the male and keep the best baby produced. If it is female, they breed to its father, if male, it is bred to its mother. They then take the best of this litter and breed them together.

Once this litter has matured, it is a good idea to look for an outcross. The best choice is a rat or mouse who excels where your line has faults. Breed it to your best opposite sex rat or mouse and start the procedure all over.

As far as inbreeding goes, I have heard of people doing it for 50 or more generations with no problems. What inbreeding does is amplify whatever recessive traits are hidden within the rat or mouse’s genetic pool. If you heavily inbreed, you will see any problems that are there and you can then get rid of them. If you never inbreed, you will not see the problems and they will be passed along until one day they mysteriously appear out of thin air.

Many people linebreed, which is a little less likely to produce problems. They take rats or mice that are related, but not closely (aunt x nephew, half brother x half sister, cousins, etc.) and breed them.

Either way, inbreeding is not a “bad” thing. It is simply a breeding tool, although close inbreeding should probably be left to the experienced breeder.

Q I know Satin Rats exist, but I’ve never heard much about them, and I’ve only seen one or two at shows. Where did they come from and why are they so rare?

A Satin rats originated in Karen Robbins’ rattery. In February 1990 they appeared out of Pearl/Cinnamon Pearl stock imported from England. These rats had long, thin, shiny hair all over their bodies. Dark colored rats appeared “sparkly” while light colored ones had an antique patina to their fur.

Before announcing that she had Satin rats, Karen wanted to make sure that’s really what she had. In the process of breeding them, she discovered that trait was passed along as a simple recessive. She also discovered that these rats tended towards being extremely susceptible to respiratory problems. It was several years before she had Satins who were healthy enough to let them out to other fanciers.

Because of their health problems, Karen never had many “extra” Satin rats to let go to other breeders. The few she did let go went to a small number of dedicated fanciers. To date, Karen is the only one who has consistently worked with them.

Because the commercial pet industry has a very detrimental effect on any new variety of animal they come upon (Siamese and Blue rats being a good example), Satins have very carefully been kept out of the pet trade. They also are not nearly as distinctive as Satin mice, and often the average pet owner has difficulty telling them apart from normal rats.

Satin rats have come a long way from what they were 10 years ago. Though a little more delicate than your average rat, their health has improved dramatically. They will probably always be a “fancier’s” animal since they are not so astoundingly distinctive that pet owners will clamor for them. More and more people are asking about them, however, and with more interest comes more breeding. Who knows, we may see an increase in their numbers in the near future.

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