This article addresses the aspect of population size on healthy breeding in dog breeds, genetic disorders and selection.
Excerpts... "In both large- and small-population breeds, genetic diversity can be lost if breeders do not utilize dogs from the breadth of the gene pool. This is most evident in the popular sire syndrome." "Health-conscious selection through breed-appropriate genetic screening of prospective breeding individuals is the most important aspect of improving and maintaining the genetic health of any breed, regardless of its population size."
Internal link: AKC Gazette-January 2018-J.Bell, DVM-Breeding By the Numbers