Aggressive breeds of dogs come in all sizes. It is the inbred tendencies from generations of working as herders and guard dogs that get most of them on the aggressive list. There are some exceptions to the rule. It is not that these breeds want to be mean, they just think it is the right way to be. In most cases, proper training will help them become more social.
The Chow Chow was originally bred to be a hunter and guard dog. They have been traced back to China in 200 B.C. The Chow Chow is a medium-size dog, about 20 inches high. The Chow Chow is a one-person dog, even if it is part of a large family. They do not like strangers at all and will bite without giving any warning.
Old English Sheepdogs
The Old English Sheepdog originated in England in the 18th century for the purpose of herding and guarding sheep. It is this instinct to protect its charges that make is aggressive to strangers. They consider their owners to be their herd and will guard them against anyone who comes too close.
Giant SchnauzersGiant Schnauzers were bred in Germany to herd sheep, just like the English Sheepdog. They are dominate, the boss and will challenge strangers. They are very protective of their family and will do anything to keep them safe from a supposed danger.
Jack Russell Terriers
Jack Russell Terriers need to be trained from the very beginning to understand that you are the boss or they will think they are the leader. The Jack Russell was bred as a hunter, and he will snap and nip at humans like he would game. They will also pick fights with other dogs and fight to the death if allowed.
Cocker Spaniels are susceptible to a genetic disease known as “rage syndrome.” This is dangerous because they will strike out at family members as well as strangers. Cockers that do not have the syndrome are great pets. You have to check with the breeders to make sure there is no genetic trait in the puppy.
The Miniature Pinscher and the Doberman Pinscher are both descended from the German Standard Pinscher. The Miniature Pinscher is not a miniature version of the Doberman. It is a breed of its own, but since they share the same ancestor, they have the same aggressive personality. Add to that the fact that the Miniature Pinscher is small and feels it needs to defend itself and you have one aggressive canine.