The following info was written by Franklin Albertsen.
Most livestock breeders divide inbreeding into 2 or 3 loosely defined categories, according to how closely related to each other the animals being mated are. Even so those divisions are rather vague and individual breeders often can't agree on how to classify. Most of us use inbred to indicate matings of sires and dams much more closely related than the average of the population from which they are selected, and continuous use of those animals over a long period of time in very small, closed herds or flocks. Think how concentrated and narrow the gene pool is after so many years of related matings. It takes ruthless culling and selection to maintain productive animals, but they breed like a "rubber stamp".
Closebreeding is the mating of closely related animals - - such as sire to daughter, son to dam, brother to sister. Usually just for a generation or two to intensify some desired trait - - or as many breeders would say "it takes a double shot to lock it in." Continual, repeated use of close bred animals (from the same mating population or strain) results in inbreeding. Linebreeding is the mating of more distantly related individuals which share a common ancestor (which was highly prized or very productive) - - such as a grandson mated to granddaughters (cousins) or nephew to aunt, etc. Linebred animals represent individuals within a "family".
Inbreeding is the fastest method in animal breeding to bring to light defects or unwanted characteristics so they may be culled (eliminated). The key to success and avoiding the many problems alluded to in the typical animal breeding texts is simply to not tolerate the use of any breeding stock displaying questionable problems. Most of our strains were developed by those old-time master breeders with inbreeding. That's why they bred so true for them. In addition they had alot of patience as they worked to develop those strains. Many literally spent a lifetime doing so. Our problem is that today everyone wants everything "right now". The person who constantly cares for his stock by doing his own chores daily, makes the matings himself, and observes and mentally makes note of everything he observes has a tremendous advantage over companies where each step in the chain of production is done by a different individual whose own motivation is often simply his pay check.
I have maintained a flock of Sweetgrass colored birds for about 35 years with never more than one or two trios at a time and very few outcrosses, also a couple trios of genuine, pure, intensely inbred Beltsville Whites, they have never exceeded 6 breeders (2 trios) and are still very hardy and fertile. I can certainly agree with the desire for identification. We can't remember everything we note with our brain - especially as more and more years pass. But the real value of it is for your in-flock use. Documentation really helps in making decisions. However, pedigrees are only as valuable as is the accuracy and integrity of the person recording them. Many pedigrees are worth no more than the paper they're written on.
Now I realize that color markings are the trademark of each variety, but the conformation, hardiness, and productivity of the birds is really more important than just being the desirable color. Remember, turkeys were originally bred for meat purposes (to be eaten), and I honestly feel that if we don't keep this in mind as we attempt to preserve our various strains, there is really no point in doing so. Therefore, make sure you keep adequate meat on the breast.
With all this said, if you're still worried about inbreeding, establish 4 or 5 pens of birds (1 tom and 4 or 5 hens per pen with a spare full-brother tom as a backup for each pen). Number or letter each pen. Replacement females each year go back into the pen their parents were in. Replacement sons from pen "A" go to "C", from pen "B" to "D", from pen "C" to "E", from pen "D" to "A", and from pen "E" to "B" each year. This can be continued for many years, maintains a high degree of relationship in your strain, but avoids real close inbreeding.