Complex sentence: The Australian Cattle Dog was, until recently, bred for purpose-directed aggression, and though remnants of that aggression still characterise the breed, the aggressive traits are being systematically bred out to accommodate the breed's new role as a household pet.
Split into simpler sentences: The Australian Cattle Dog was, until recently, bred for purpose-directed aggression. Remnants of that aggression still characterise the breed, although the aggressive traits are being systematically bred out to accommodate the breed's new role as a household pet.