All purebreeds have thier own unique problems that should be checked for. I'm not familiar with all the Shitzu's but your vet should be. I would not breed any female before 18 months of age after 2 would be my preference. Temperment for a small dog is often overlooked. Most of the Shitzu crosses I have seen eat thier own poop. It would be something I would not want breed into the next generation.