One way to avoid these recessive lethal genes is to outcross as much as possible. Unfortunately, the line into which you outcross may carry the very same genes that you are trying to avoid. It is quite possible, however, to weed out genetic faults in even the most heavily inbred lines.
Scientists do it all the time.
This allows scientists to study these animals without the interference of genetic differences between individuals. These animals carry no lethal genes and are extremely healthy in every way except one. They need to be kept in extraordinarily clean, nearly sterile environments because their immune systems are not capable of fighting off a normal range of diseases. The immune system of all animals is absolutely dependent on genetic diversity. There are basically two kinds of immune responses, each is due to a specific antigen receptor molecule produced by one kind of white blood cell.