@mvdperez
I am not sure where you got your information, but no, breeding a dog or cat or horse or cow or pig or any mammal to another breed does one thing only-- produces mixed offspring that time. When you breed to another purebred, those offspring are not "ruined bloodlines". They are just as pure as before.
IOW, if your XYZ show queen mates with Mr Doodles, the neighborhood stray, the kittens produced are mixed. Obviously not XYZ purebreds.
Next time, you breed your XYZ queen to a purebred XYZ tom, the kittens produced are PUREBRED XYZ. Their bloodline isn't ruined. They have no dna from the previous litter.