[QUOTE=NOMIOMI1;6489492]
This is the failure of EVERY breed out there (to close books and only allow the variations within the genes that are there).[/QUOTE]
Interestingly, although some breeds such as the TB and Arab have closed books, from a genetics point of view, that is not a prerequisite for operating a a breed.
Somewhere else (another thread?) I commented that genetically speaking, an animal of >7/8 (>87.5%) of the same “blood” is considered “pure”. This is based upon the supposition that at that level, the animal will breed “true” to a greater extent, and is related to 5 generations (with some lesser evolved characteristics, 3 generations will breed “true”).
It is therefore quite possible to operate a breed, but still allow outcrossing to introduce new characteristics - this is known as an “open studbook” and is achieved by operating a “main” stud book, in which animals of >7/8 blood are recorded, while there are other stud books record animals of lesser blood.
This is related to the “F” structure is created in genetics. Let us suppose that we have such a breed as described above, and we are introducing an outside animal to that breed. That animal will be termed an F0. When crossed with another animal of a different breed but which has also been deemed acceptable for use (one cannot cross TB on TB and be considered to be evolving another breed for example - it’s still a TB!!), the resulting offspring will be an “F1”. An F1 crossed on an F1 produces an F2, and so on. F5 is the first generation of “pure”. When crossing, one can only go one generation higher than the lowest common denominator, so crossing an F1 on an F4 results in an F2, and similarly a main stud book animal crossed on an F1 will also produce an F2.
The above does raise an interesting point, as the vast majority of sport horse breeders use an outcross, seeking heterosis or “hybrid vigour” (which is often excellent), but this action does not stabilise the resulting gene pool (i.e. those characteristics in that animal will have a reduced chance of being passed on to the next generation, compared to an F4 animal’s characteristics).
Although warmbloods are considered a “registry” rather than a “breed”, the “open stud book” structure is essentially how they operate. There is however, typically, a greater amount of outcrossing, so fewer animals would get to an F5 or greater status. The major key to being considered a breed of course, rather than a registry, is that a significant (usually greater) number of animals comprise the “pure” (F5 or greater) portion of the stud book - a “breed” with a greater number of animals <F5 may be considered an “evolving breed” (if that is their aim) or a registry.
This is completely OT to the original thread, for which I apologise, but it is (IMO) an interesting point that is often misunderstood when breeds, stud books and genetic input are being discussed.
OK - Carry On! 