Foundation bloodstock or foundation stock are horses that are the progenitor, or foundation, of a new horse breed or a given bloodline within a breed. The term is also used in a similar manner when discussing purebred dogs. A group of animals collectively may be referred to as foundation bloodstock when one breed, or group of breeds, provides the underlying genetic base for a new breed. This is particularly common in older breeds where a written stud book was not created until after the breed phenotype was well-established.
However, other breeds can be traced to specific named animals. In these cases, a "Foundation sire" is a stallion or male horse who is identified as an original progenitor of the breed, and a "Foundation mare" is a female. There are usually few foundation sires, but several mares, though in many cases, foundation mares are not always identified in old pedigree records. In most cases, breeds that require that all members trace to specific foundation stock have a closed stud book and do not allow crossbreeding to other animals. Some breeds that may have named foundation stock but are still allowing outside bloodlines to contribute to the genetic base of the breed have at least a partially open stud book. An example of a partially open stud book is the American Quarter Horse, which still allows limited registration of animals with one Quarter Horse parent and one Thoroughbred parent. Many warmblood breeds also have open stud books, where horses that are registered may be of a variety of bloodlines, but must pass a rigorous studbook selection process.
The term "Foundation" when applied to horses also may be used to refer to animals of a phenotype that resembles that of the original foundation stock, particularly when the modern look of the animal is different. It may also refer to animals tracing only to a select number of the oldest foundation bloodlines, particularly when newer breeding has been added that changed the original phenotype.
Some breeds, such as the Morgan horse, have a single named foundation sire, while others, such as the Lipizzan, may have several. In some cases, particularly very ancient horse breeds, not even all foundation sires may be known. However, in breeds with a well-documented breed registry, nearly all foundation animals may be identified. For example there are three major foundation sires of the Thoroughbred, and another 24 or 25 minor foundation sires, along with 74 foundation mares. An example of a breed formed by foundation stock from other breeds, but not necessarily all from named individual animals is the Hackney horse, with bloodlines contributed from Thoroughbred and Norfolk Trotter. In other cases, where a breed or landrace is older than any written records, the foundation bloodstock is sometimes described by myths or legends, such as the mythical horses of Mohammad, known as Al Khamsa or "the five," said to be the foundation mares of the Arabian horse.
An example of a foundation bloodstock pedigree line within a breed would be the "Crabbet" lines from the Crabbet Arabian Stud in England. These animals were bred by the same program for 92 years, were exported worldwide, and had a substantial impact on the breed. Some Arabian breeders today not only breed purebred horses, but horses descended only from this breeding program.
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