A purebred dog typically refers to a dog of a modern dog breed with a documented pedigree in a stud book and may be registered with a breed club that may also be part of a national kennel club.
Purebred dog may also be used in a different manner to refer to dogs of specific dog types and landraces that are not modern breeds. An example is cited by biologist Raymond Coppinger, of an Italian shepherd who keeps only the white puppies from his sheep guardian dog's litters, and culls the rest, because he defines the white ones as purebred. Coppinger says, "The shepherd's definition of pure is not wrong, it is simply different from mine." However, the usual definition is the one that involves modern breeds.
The earliest use of the term "pureblood" in English referring to animal breeding, according to the Online Etymological Dictionary, was in 1882 and "pure bred" in 1890. The Merriam-Webster Online Dictionary dates the use to 1852.
Purebred dogs are pedigreed members of modern breeds. These dogs may be registered with breed club. The breed clubs may be an open stud book or a closed stud book, the term can be interpreted to either. Usually the breed club is also associated with a kennel club (AKC, UKC, CKC etc.). However dogs who are registered with a breed club are usually referred to as "registered". Some use the term exclusively for a dog that has also been registered with a breed club, but more often it is used simply as a generic term to refer to dogs who have known pedigrees within a standardized breed. A dog that is purebred cannot be interpreted to mean it is high-quality dog. It is no reflection on the quality of the dog's health, temperament or sagacity, but merely a reference that the dog has known parentage according to the breeder. While some breed clubs can now guarantee parentage through DNA testing for the most part all breed clubs must rely exclusively on the breeder's word and choice of parentage. In the early years of the kennel club concept this was not at issue since dog breeding was only done among the extremely wealthy and their reputations were at stake. However in this modern age of breeding one must be aware that even a DNA proven purebred and registered champion who has won national competitions can have serious health issues.The closed stud book requires that all dogs descend from a known and registered set of ancestors; this results in a loss of genetic variation over time, as well as a highly identifiable breed type, which is the basis of the sport of conformation showing. In order to enhance specific characteristics, most modern purebred dogs registered with closed stud books are highly inbred, increasing the possibility of genetic-based disease.
The open stud book, meaning some outcrossing is acceptable, is often used in herding dog, hunting dog, and working dog (working dog meaning police dogs, assistance dogs, and other dogs that work directly with humans, not on game or livestock) registries for dogs not also engaged in the sport of conformation showing. Outcrosses with other breeds and breeding for working characteristics (rather than breeding for appearance) are assumed to result in a healthier dog. Overuse of one particular stud dog due to the desirability of the dog's working style or appearance leads to a narrowing of genetic diversity, whether the breed uses an open stud book or a closed stud book. The Jack Russell Terrier Club of America states, "Inbreeding favors genes of excellence as well as deleterious genes." Some open stud book breeds, such as the Jack Russell Terrier, have strict limitations on inbreeding.
Dog crossbreeds (first generation crosses from two purebred dogs, also called dog hybrids) are not breeds and are not considered purebred, although crossbreds from the same two breeds of purebreds can have "identical qualities", similar to what would be expected from breeding two purebreds, but with more genetic variation. However, crossbreds do not breed true (meaning that progeny will show consistent, replicable and predictable characteristics), and can only be reproduced by returning to the original two purebred breeds.
Among breeds of hunting, herding, or working dogs in open stud book registries, a crossbred dog may be registered as a member of the breed it most closely resembles if the dog works in the manner of the breed. Some hunting, herding, or working dog registries will accept mixed breed (meaning of unknown heritage) dogs as members of the breed if they work in the correct manner, called register on merit.
For mixed breed (unknown heredity), crossbred (from two different purebred breeds), or otherwise unregistered purebred pet dogs there are available many small for-pay internet registry businesses that will certify any dog as a purebred anything one cares to invent. However, new breeds of dog are constantly being legitimately 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. Only documentation of the ancestry from a breed's foundation stock determines whether or not a dog is a purebred member of a breed.
A showdog is a purebred dog that participates in dog shows with its owner or handler.
The term showdog is commonly used in two different ways. For people in the dog fancy, a showdog is an exceptional purebred dog that conforms to breed type, and an outgoing, high energy character. For people who have no interest in dog shows, the term "showdog" is often used facetiously to refer to a dog whose only attributes are in its appearance. Raymond Coppinger says, "This recent breeding fad for the purebred dog is badly out of control.".
Dog shows (and the related sport of Junior Handling for children and young people) continue to be popular activities; a single show, the 2006 Crufts dog show alone had 143,000 spectators, with 24,640 purebred dogs entered, representing 178 different breeds from 35 different countries. The sport of conformation dog showing is only open to registered purebred dogs.
Purebred dogs represent to many commentators the attitudes of the late Victorian era, when dog breeding first became popular and when most modern breeds originated. Purebred dogs were bred from a narrow set of ancestors, and an idea developed that this made them superior in appearance. Englishman Francis Galton used the term eugenics to refer to his ideas for applying domestic animal breeding techniques to humans, to produce a 'pure' and 'good' elite; the idea became an intellectual fad, promoted by people such as dog writer Leon Fradley Whitney, Purebred dog breeders of today have therefore been accused of following "a breeding paradigm that is anachronistic in the light of modern genetic knowledge, and that first arose out of a misinterpretation of Darwin and an enthusiasm for social theories that have long been discredited as scientifically insupportable and morally questionable."
Modern breeders and owners of pedigreed dogs, however are more interested in the real or imagined early history of their favourite breed's development. Reputable breeders attempt to produce the healthiest dogs the limited gene pool will allow, and buyers of purebreds primarily are interested in a puppy whose adult size, appearance, and temperament are predictable. In addition, tens of thousands of people worldwide enjoy the sport of dog showing, which is restricted to dogs registered within their own kennel clubs.
Genetic conditions are a particular problem for dogs from registries whose stud books are closed. Many national kennel clubs prohibit registering dogs that have or carry certain genetic illnesses. Some of the most common conditions include hip dysplasia, seen in large breed dogs, von Willebrand disease, a disease that affects platelets that is inherited in Doberman Pinschers, entropion, a curling in of the eyelid seen in Shar Peis and many other breeds, progressive retinal atrophy, inherited in many breeds, deafness, and epilepsy, known to be inherited in Belgian Shepherd Dogs, German Shepherd Dogs, Cocker Spaniels, and St. Bernards. In 2008, the BBC ran a documentary on the health problems in pedigree dogs.
Most Kennel Club breeds that exist today were chosen from existing land-race breeds in the late 19th century. How those dogs appear now however have been customized to fit within the breed club's chosen description of them. To do this, required selective breeding and rigorous culling. This created a genetic bottleneck that some people think will render breeding from closed stud books not viable. Suggestions for improvement have included outcrossing (opening studbooks) and measuring and regulating inbreeding. There are some breeders who take care to ensure that the dogs they breed have not been bred to too many other dogs so that the genetic pool does not shrink from everyone breeding to a popular sire. There are a great deal that are merely breeding two "papered" dogs assuming that is all they need to do.
Books on choosing a puppy advocate for "purebred' dogs, as long as they come from breeders who are willing to invest the time and money in producing healthy dogs that they are willing to guarantee. "The difference is that purebred breeders know what to expect", writes Chris Walkowicz in The Perfect Match. Stephen Budiansky in The Truth About Dogs writes, "It is true that the standard criticisms leveled against inbreeding are not always well informed from the point of view of modern genetics." He continues, "Curing the problems that inbreeding has engendered in purebred dogs will require more subtlety than either most breeders or their more vocal critics have so far displayed."
Hungarian ethologist Vilmos Csányi sees purebred dog breeders, in efforts to meet breed standards, increasing the extent of inbreeding and thereby reducing the breeds' desirable attributes; "This process appears to be unstoppable," he says.
However, science continues to get better and enables breeders to test for genetic diseases. Where breeders were only able to detect afflicted animals in the past, now DNA tests can be run and only animals without affected genes can be bred to produce stronger breeds.
Some types of pedigreed dogs are frequent targets of Dognapping (the crime of taking a canine from its owner) the profit from which can run up to thousands of dollars.