The term purebred is occasionally confused with the proper noun Thoroughbred, which refers exclusively to a specific breed of horse, one of the first breeds for which a written national stud book was created since the 18th century. Thus a purebred animal should never be called a "thoroughbred" unless the animal actually is a registered Thoroughbred horse.
However, over time, there are also concerns that breeding from too small a gene pool can lead to inbreeding and the development of negative characteristics or even a collapse of a breed population due to inbreeding depression. Hence, there is continuing tension within many purebred animal breeds over the question of when a breed may need to allow "outside" blood in for the purpose of improving the overall health and vigor of an animal breed.
Sometimes the word purebred is used synonymously with pedigreed, but purebred refers to the animal having a known ancestry, and pedigree refers to the written record of breeding. Not all purebred animals have their lineage in written form. For example, until the 20th century, the Bedouin people of the Arabian peninsula only recorded the ancestry of their Arabian horses via an oral tradition, supported by the swearing of religiously-based oaths as to the asil or "pure" breeding of the animal. Conversely, some animals may have a recorded pedigree or even a registry, but not be considered "purebred." Today the modern Anglo-Arabian horse, a cross of Thoroughbred and Arabian bloodlines, is considered such a case.
A purebred dog is a dog of a modern breed of dog, with written documentation showing the individual purebred dog's descent from its breed's foundation stock. In dogs, the term breed is used two ways: loosely, to refer to dog types or landraces of dog (also called natural breeds or ancient breeds); or more precisely, to refer to modern breeds of dog, which are documented so as to be known to be descended from specific ancestors, that closely resemble others of their breed in appearance, movement, way of working and other characters; and that reproduce with offspring closely resembling each other and their parents. Purebred dogs are breeds in the second sense.
New breeds of dog are constantly being created, and there are many websites for new breed associations and breed clubs offering legitimate registrations for new or rare breeds. When dogs of a new breed are "visiblily similar in most characteristics" and have reliable documented descent from a "known and designated foundation stock" they can then be considered members of a breed, and, if an individual dog is documented and registered, it can be called purebred.
Written and oral histories of various animals or pedigrees of certain types of horses have been kept throughout history, though breed registry stud books trace only to about the 13th century, at least in Europe, when pedigrees were tracked in writing, and the practice of declaring a type of horse to be a breed or a purebred became more widespread.
Certain horse breeds, such as the Andalusian horse and the Arabian horse, are claimed by aficionados of the respective breeds to be ancient, near-pure descendants from one or the other of the original four wild prototypes, though absent a full mapping of the horse genome and other DNA research, such claims are difficult to prove or disprove.
The list of cat breeds is quite large: most cat registries actually recognize between 30 and 40 breeds of cats, and several more are in development, with one or more new breeds being recognized each year on average, having distinct features and heritage. Owners and breeders compete in cat shows to see whose animal bears the closest resemblance to the "ideal" definition, based on breed type and the breed standard for each breed.
Some original cat breeds that have a distinct phenotype that is the main type occurring naturally as the dominant domesticated cat type in their region of origin are sometimes considered as subspecies and in the past received names as such, although this is no longer supported by feline biologists. Some of these cat breeds (with their invalid scientific names for historical interest) are:
Many times, domesticated species live in or near areas which also still hold naturally evolved, region-specific wild ancestor species and subspecies. In some cases, a domesticated species of plant or animal may become feral, living wild. Other times, a wild species will come into an area inhabited by a domesticated species. Some of these situations lead to the creation of hybridized plants or animals, a cross between the native species and a domesticated one. This type of crossbreeding, termed genetic pollution by those who are concerned about preserving the genetic base of the wild species, has become a major concern. Hybridization is also a concern to the breeders of purebred species as well, particularly if the gene pool is small and if such crossbreeding or hybridization threatens the genetic base of the domesticated purebred population.
The concern with genetic pollution of a wild population is that hybridized animals and plants may not be as genetically strong as naturally evolved region specific wild ancestors wildlife which can survive without human husbandry and have high immunity to natural diseases. The concern of purebred breeders with wildlife hybridizing a domesticated species is that it can coarsen or degrade the specific qualities of a breed developed for a specific purpose, sometimes over many generations. Thus, both purebred breeders and wildlife biologists share a common interest in preventing accidental hybridization.
Breeding Values, Accuracies, and Rank Changes Using Purebred and Combined Purebred and Crossbred Information in Swine
Apr 01, 2006; Abstract A data set including 2,002 Purebred litter records and 14,583 crossbred litter records from a swine production...