The genetic bottlenecks created by closed breed registries and popular sire effects have reduced genetic diversity in many dog breeds, increasing susceptibility to hereditary disease and reducing overall health resilience.
Breed genetic diversity is a welfare issue that operates at the population level but manifests in individual animal health and wellbeing. Breeds with very low genetic diversity are more susceptible to hereditary disease, have reduced immune competence, and may face breed-wide vulnerability to emerging pathogens. The closed registry system that prevents crossbreeding to maintain breed purity has created these vulnerabilities over generations of selection from small founding populations. Opening registries to outcrossing — as has occurred in some breeds including the Dalmatian — can restore diversity and improve breed health over generations, but requires overcoming the cultural attachment to breed purity that drives resistance to genetic reform.