Blue heelers, also called Australian cattle dogs, are a medium-sized, energetic dog that was originally bred to herd cattle. They have dense, coarse hair. When they are kept as a pet rather than a working dog, they need lots of exercise and activities to keep them occupied or they get bored and destructive. As they herd cattle by nipping at them, they can be a nippy dog and will need chew toys. They can become very loyal to their owners and aggressive to anyone else they consider a threat.