Genetic sustainability.

As with so many pedigree breeds, Leonbergers are genetically constrained by what was a relatively small founding population. The difficulties of keeping such large dogs alive during both World Wars added to this genetic pressure by again dramatically reducing numbers. Today’s worldwide Leonberger population has been estimated to be somewhere in the region of 40,000 individuals, which may seem like a large number at first. But the reality is that it is probably best to consider this to be similar to 40,000 first cousins because of the inter-relatedness of the overall population, and this can lead to additional health vulnerabilities due to lack of genetic diversity. 

Generally speaking, less than %10 of any given generation will be bred from, which means that the genetic contribution of the remaining %90 is lost to future generations. This means that with each new generation, the genetic diversity reduces further, and this often gives rise to more and more genetic illness risk within the population. It is the same for all pedigree breeds within the closed gene pool breeding system.