Their aim is to improve data exchange between studbooks and countries. These figures make Oldenburg one of the largest studbooks in Germany. Besides EEP Safaripark Beekse Bergen also participates in European Studbooks (ESB). The Dutch studbooks were closed on 1 February 1971. Open Studbooks and registers dogs on merit is they meet the breed standard. However, he was eventually approved with several studbooks, including the Oldenburg. Big Star is a sought after stallion, approved in 21 studbooks. As with most warmblood studbooks, only stallions who meet certain standards are permitted to breed. The studbooks comprise about 2,500 mares and 80 stallions. Suggestions for improvement have included outcrossing (opening studbooks) and measuring and regulating inbreeding. The zoo maintains studbooks for black and Indian rhinoceroses and gaurs. She kept studbooks for gibbons and chimpanzees. In the Northern Basque Country, two studbooks for the Pottok were set up in 1970. Studbooks for the English foxhound have been kept since the 18th century. Pedigrees were recorded in Celle's studbooks as early as the end of the 18th century.