1) Does getting attacked as a puppy automatically create a reactive dog?
Not necessarily. Much depends on the dog's native temperament. Some puppies can recover from an attack and be none the worse, if they have very strong nerve and a lot of natural confidence, high stress thresholds. As long as the owner doesn't let it happen repeatedly, a strong pup will probably be fine. Other pups with weaker temperament will be shaken to the core after an attack and become fearful, reactive and possibly aggressive.
Does "dog reactive" automatically translate to aggression?
A dog that growls, barks, and carries on when it sees another dog is not necessarily going to attack if given the chance. Half the time, it's all bluff and meant to say "Get away from me!" However, if a dog learns to solve his problems through aggression "I'm gonna take you out before you can take me out", you have a serious problem.
So if a dog is attacked during the imprint stage, and ultimately ends up afraid, what determines the "fight or flight" response?
Why would some dogs become aggressive, and others run away?
Temperament, nerve, confidence, thresholds... all of which the dog is born with (or without). Also, past experience (if any) may determine the dog's behavior in a fight-or-flight situation.
What determines the "fight or flight" response has to do with adrenaline and other stress hormones. That is mostly controlled by genetics, but also by past experience. With some dogs, it takes a lot to get them to the point where they feel the *need* to fight or flee--another dog could be barking in its face and the pup just wants to play--he doesn't see a threat. With others, it takes practically nothing to get them into a fit of terror. You just have to know your dog, whether the temperament and nerves are strong or weak.
There is a rather famous experiment done in Russia with foxes on fur farms--you may have heard of it. A fur farmer wanted to raise a fox that was easier to handle, so he bred only the friendliest (least fearful) foxes. No extra attention was given and the foxes were no more used to people--the temperament change had to be genetic, not learned. So, the foxes that cowered in the back of the cage and snarled were made into coats, and the foxes that did not were bred.
Over many generations, the foxes became naturally friendlier, until they were downright doglike. What was interesting (and this is only a side note to the discussion) is that they started to APPEAR doglike as well. The ears became floppy, the tails became shorter and held over the back, the coats became spotted. Their heads became smaller, their bones finer. These were all physical traits that were not selected for, but they came about naturally as a result of "tameness".
The key to the temperament and physical changes, they found out, is the production of adrenaline and other stress hormones that trigger the "fight or flight" response--the tame foxes produced less. It appears that these hormones are linked to certain physical traits other than temperament, and they occur during early development of the embryo.
There is now a pet trade in these tame foxes from Russia, if you want one I think they are around $10K each.
Domesticated silver fox - Wikipedia, the free encyclopedia