P_Smith
Not necessarily, I know people of who raise show quality English Mastiffs who average life span is 16 years and another who raises Newfoundlands that regularly hit their late teens. It's really all in if the parents and grandparents and even great great grandparents have been treated conventionally. Hence the shorter lifespans and diseases at an earlier age. RE: Epigentics.
On another note, I know a lot more mix breed dogs that are inbred than show quality purebreds. Again, all depends on the breeders 'methods'.