Analysis of the canine genome and canine health: a commentary.

The widespread consensus among biologists is that, with a few exceptions, inbreeding leads to a loss of biological fitness. Animals in an inbred lineage are less likely to survive and less likely to reproduce than animals in more outbred lineages. This has been demonstrated many times in well-studied, naturally outbreeding species. Inbreeding can result in reduced fertility both in litter size and sperm viability, developmental disruption, lower birth rate, higher infant mortality, shorter life span, increased expression of inherited disorders, reduction of immune system function and cancer (Charlesworth and Willis, 2009). Many of the effects of inbreeding have been found in isolated populations of wolves, the wild ancestors of domestic dogs, with detrimental effects (Laikre and Ryman, 1991; Smyth et al., 2006). Severe inbreeding depression has been documented in Scandinavian wolves that had passed through an extreme bottleneck (Liberg et al., 2005). During their first winter after birth the number of surviving pups per litter was strongly and inversely correlated with the level of inbreeding in the pups. There have been few comparable studies in dogs. Rehfeld (1970) showed a correlation between neonatal death and level of inbreeding in pups from a highly inbred Beagle colony, whilst studies of Foxhounds (Wildt et al., 1982) and of Irish wolfhounds (Urfer, 2009) showed the greater the degree of inbreeding the smaller the litter size. A range of diseases including autoimmune conditions, neoplasia and osteochondrosis show significant associations with coefficient of inbreeding measured on