It is highly doubtful improved breeds.
Breeding is not in place. The handlers are constantly looking for new ways and opportunities to improve certain breeds of dogs, to adjust them for the needs of man. That is why the current breeds of dogs differ significantly from the same species that existed at the beginning of the last century.
People are playing with nature, trying to put her own conditions and any ways to achieve this. Victims of these animals become, as with the changes in appearance they have changed internally. So, some animals become different, uncharacteristic for their disease.
Recently in the Internet appeared the illustrations from the book, 1915, V. E. Mason “Breeds of all Nations”. They perfectly demonstrate what was the result of centuries of breeding work on “improving” breeds.
Bull Terrier
Bassethound
Boxer
English bulldog
German shepherd
Pug
The St. Bernard
Dachshund
