I agree that a good diet, exercise, and vet checks are extremely important to make the most of your dogs health, however, they will not prevent the genetic diseases that are rampant in poor breeding. You need to become aware of such illnesses as liver shunt, and know the symptoms, so that if your dog is affected at least he will be able to be treated as soon as possible, lessening the damage. Here are some of the illnesses affecting Yorkies, some are genetic, and others are viral.
Yorkshire Terrier
By the way, most of us have had dogs that were that result of poor breeding, and that is why many of us have become advocates for responsible breeding. Best of luck with Louie.