The breed is a prominent participant in conformation shows for purebred dogs. The ratio of pedigree/purebred cats to random-bred cats varies from country to country. The Morkie is a cross between a purebred Yorkshire terrier and a purebred Maltese. Dogs that are not "purebred" are not necessarily a mix of such defined breeds. Maintaining correct data is important for purebred dog breeding. This allows for identification of purebred species by making sure that breeds are not misidentified. In cattle, some breeders associations make a difference between "purebred" and "full blood". In 2004, a study looked at the microsatellites of 414 purebred dogs representing 85 breeds. These are dogs created deliberately by crossing two purebred dogs. A few mare mules have produced offspring when mated with a purebred horse or donkey. Reveille V was a descendant of a championship purebred Rough Collie. Those who appeared purebred were used for breeding, others weeded out. Sometimes purebred horses are incorrectly or inaccurately called "thoroughbreds". As with all purebred dogs, PWDs are vulnerable to certain genetic defects. In 1884, Robinson imported purebred Arabian horses.