Snip from New York Times article by Martin Fackler on the downsides of extreme inbreeding of pets in Japan:
Rare dogs are highly prized here, and can set buyers back more than $10,000. But the real problem is what often arrives in the same litter: genetically defective sister and brother puppies born with missing paws or faces lacking eyes and a nose.reg-free Link to story. Above, a mutant Japanese chihuahua bred so that its fur will have a blue hue. Eh, whatever. But how do they taste?
There have been dogs with brain disorders so severe that they spent all day running in circles, and others with bones so frail they dissolved in their bodies. Many carry hidden diseases that crop up years later, veterinarians and breeders say.