Creating A Bloodline

A bloodline is a series of animals with ancestors in common. In rats, a bloodline is created for a specific purpose: to bring forward and continue a certain trait or traits. Forming a bloodline requires careful planning, judicious inbreeding, and selection to truly bring out the full potential.

What a bloodline is not is a group of animals who are all the same color or markings, who do not have many ancestors in common. If you see a pedigree with a lot of outcrossing in it, that rat is not the result of a bloodline. Breeding animals with traits but not ancestors in common is a very different tactic of breeding than making a bloodline.

Why create a bloodline?

In short, for security. When you are breeding a bloodline of animals, you are working with known factors, both positive and negative. By inbreeding animals with common ancestors together, you are going to "set" traits, and bring out hidden recessives. You are going to be able to predict litter population with a greater degree of certainty. You are going to know what negatives you are likely to have pop up. Additionally, you should be getting progressively higher quality offspring, if you are making good selection of type, color and health to breed every generation.

Isn't inbreeding bad?

Not really. In fact, every breed or sub-breed of animal you see has been, for the most part, created by inbreeding. A mutation of color or type crops up, and someone breeds that animal to its own offspring and voila, you have a new type of that animal to work with. Rats have shown to be able to easily close inbreed (mother-son, father-daughter, brother-sister) for more than 20 generations before any abnormalities or ill health begin to show up. In fact, almost all laboratory "strains" of rats are specifically kept very closely inbred, because it produces very uniform animals in type, genetics and health, which reduces variation in experimental data.

Inbreeding allows us to "set" traits, by combining animals who are very much alike and are therefore less likely to throw us a "wild card" when we breed them. A rat with a very nicely shaped head, when bred to his own daughter or sister with a similarly nice head, is likely to throw offspring who have heads that are as good or better than their parents.

A rat with a very nicely shaped head, when bred to an unrelated rat with a very nicely shaped head, has a chance of throwing just about anything. Even though both parents have nice heads, without knowing what the aunts, grandparents, and siblings of those rats look like, you do not know what you are going to get. All that unrelated rat's offspring could end up looking like her father… who might have had a really narrow, ugly head. Inbreeding reducing this chance, and the longer it continues, the stronger the factor of prediction becomes.

What about setting bad traits?

This is the biggest disadvantage to inbreeding. When you breed a brother and sister together whose mother was carrying - but not exhibiting - a genetic disease, your chances that they will have babies exhibiting or carrying that disease is much higher. On the one hand, this is a very bad thing: no one wants to be breeding sick litters! On the other, it is good to find out what the line is carrying as soon as possible so that you can make the hard decision to either end it, or spend years trying to work that ailment out of your lines. Nothing is more heartbreaking than spending several years building up a line that has to be abandoned by an unforeseen genetic issue.

The other kind of "bad traits" that you can set are visual ones. Your rat with the awesome head and his daughter with the awesome head may be really stunning but have only mediocre tails. You can breed them together and get some babies with pretty awful tails. Continue breeding those rats with the great heads and mediocre tails, and you can set both traits into that bloodline so that they are very strong and prominent… and hard to breed out.

Selection is, of course, of the utmost importance. You want to pick animals with the best collection of outstanding traits and as few mediocre and downright bad ones as possible. When possible, you want to pick rats that compliment one another - that play to one another's strengths and shore up each others' weaknesses. If you have a really great buck whose only weakness is a thin tail, then you want to look for the best doe you can, and preferably one with a really great tail.

How closely do we need to inbreed to establish a bloodline?

That is up to the judgment of the individual breeder. The point of inbreeding a bloodline is to be working with a known line, without a lot of unknown surprise factors, and with a lot of traits in common. A lot of times, the best animals you're going to have available to you will be a parent-offspring or brother-sister cross, and if those are the best examples of that bloodline, those are what you should use.

What about outcrosses?

Sometimes, you've set a bad trait and really need an unrelated animal to start sorting it out. Or you just feel like you've inbred the "vigor" out of your population and you really need a shot of fresh blood. Or sometimes, you'd like to add something, like a new color or coat type, to your bloodline, and need to get it from somewhere.

Your safest bet is always a related animal that has been outcrossed a generation or so back, who has the traits or improvements you need. That way you know you are dealing with an animal who is likely to breed well with your current bloodline, but who is still bringing in an injection of freshness that you're seeking.

If such an animal is not available, then you will have to make one. You want to choose an animal who will compliment your best-available bloodline animal, who shores up whatever weakness you're trying to fix, or is the best specimen of the trait you're trying to add, without introducing much in the way of new problems to fix.

The next step is to breed the best of those offspring together. In this way, you can attempt to bring any faults in the line to the surface as soon as possible. If you get any serious defects, you want to immediately stop that particular outcross. If you don't, take the best specimens from that litter and go from there. It is recommended that you spend at least a couple of generations close-inbreeding this new outcross before you use it for your main bloodline's sole outlet, just in case something unexpected and negative pops up.

The benefits of a strong, well-maintained and well-selected bloodline are clear and obvious. Most breeders will maintain at least one bloodline over the course of their rattery's lifetime, sometimes more than one. In order to truly ensure maximum chances of rats with solid health, temperament and type, a well-maintained bloodline is very nearly necessary.