Well mongrels definetley are more naturally healthier than pure breeds because they wont be proned to any genetic diseases I know this from keeping mongrels and pure breeds and other people who have kept both say it too. My grandfather loves German shepherd dogs but dosen't want to get another one as the one he has now is slowing down due to his bones in his hind quaters same as the previous one he had. He dosent want to get another one because it too heart breaking seeing them die at such a young age. I think some laws must be introduced in making sure dogs are healthy before breed. For example I'm thinking of breeding my neo mastiff but thats because shes very healthy and I have x-rayed her to find that she has very good bone structure. I have been told that they have introduced theese laws in Germany.