Selective breeding for extreme traits has reduced genetic diversity in many dog breeds, leading to inherited disease burdens that compromise welfare across millions of pets worldwide.
Reduced genetic diversity means that deleterious recessive alleles become fixed across entire breeds, so virtually all dogs of a given breed may carry or express the same inherited condition. This differs fundamentally from random individual disease and represents a systemic welfare problem. Conditions like syringomyelia in Cavalier King Charles Spaniels affect the majority of the breed and cause chronic pain. Outcrossing programmes, where approved crosses to related or unrelated breeds are permitted, have shown success in reducing disease prevalence while maintaining breed character. The welfare cost of ignoring diversity is borne entirely by individual dogs who experience lifetimes of managed chronic disease.