The widespread consensus among biologists is that, with a fewexceptions, inbreeding leads to a loss of biological fitness. Animalsin an inbred lineage are less likely to survive and less likely toreproduce than animals in more outbred lineages. This has beendemonstrated many times in well-studied, naturally outbreedingspecies. Inbreeding can result in reduced fertility both in litter sizeand sperm viability, developmental disruption, lower birth rate,higher infant mortality, shorter life span, increased expression ofinherited disorders, reduction of immune system function and can-cer (Charlesworth and Willis, 2009).Many of the effects of inbreeding have been found in isolatedpopulations of wolves, the wild ancestors of domestic dogs, withdetrimental effects (Laikre and Ryman, 1991; Smyth et al., 2006).Severe inbreeding depression has been documented in Scandina-vian wolvesthathad passed throughan extremebottleneck (Liberget al., 2005). During their first winter after birth the number of sur-viving pups per litter was strongly and inversely correlated withthe level of inbreeding in the pups. There have been few compara-ble studies in dogs. Rehfeld (1970) showed a correlation betweenneonataldeathand level of inbreeding inpups froma highly inbredBeagle colony, whilst studies of Foxhounds (Wildt et al., 1982) andof Irish wolfhounds (Urfer, 2009) showed the greater the degree ofinbreeding the smaller the litter size. A range of diseases includingautoimmune conditions, neoplasia and osteochondrosis show sig-nificant associations with coefficient of inbreeding measured onseven generation pedigrees in the Bouvier Belge des Flandres dog(Ubbink et al., 1992).