Selective breeding of horses for extreme conformation traits and breed standards has introduced heritable welfare problems across multiple popular breeds.
Equine breeding has introduced heritable welfare problems through the same mechanisms seen in companion animal breeding — selection for extreme conformation traits and founder effects from prolific sires. HYPP is perhaps the most egregious example: a single American Quarter Horse stallion passed a dominant mutation causing painful episodic muscle paralysis to hundreds of thousands of descendants before genetic testing enabled detection. Brachycephalic trends in miniature horses mirror the welfare crisis in flat-faced dog breeds, with selected animals experiencing chronic breathing difficulties. Responsible breeding requires mandatory genetic testing for known heritable diseases, exclusion of affected horses from breeding programs, and evaluation of conformation traits for functional health rather than purely aesthetic appeal.