What happens to the purebreds when you breed them:
As it is with a few species on earth, Nithian purebreds don't survive the birth of their offspring. Giving birth to a new Nithian is the greatest pleasure of their life, their body burns up, but their spirit survives and lives on watching their offspring thrive. Nithians are very bad at finding their mates so you helping them choose one is highly appreciated. Due to the disease the longer they need to wait for this occasion, the longer their suffering.