I am not a breeder but I am a RN so would encourage to start genetics and how they work since you have so many questions regarding this. You need to understand that a negative trait and a positive trait do not make a perfect match. In fact, you could have 2 perfect parents with a non-dominant trait gene, lets say blue eyes or sickle cell ( I am using human examples of course). The odds are 50% the child will have sickle cell, 25% only the trait and 25% that it will be negative for it. That is genetics and there are no guarantees. Now lets talk about Spina bifida, this has a lot to do with genetics and prenatal care etc. And what about after the pups are born, how about the swimmers. Getting a dog knocked up is as easy as a person, except the bullies are more like someone with a fertility problem. There are so many variables that could result in tragedy or perfection. I hope this helps with your decision. I would also study the rates of your female possibly dying. Are you willing to take that risk. Something to think about