It can happen in a split second when an older dog tries to attack a younger dog. This can have a very severe effect on a young dog especially when it didn’t see the attack coming and the pup was not doing anything wrong at all. Yes I have seen adult dogs do this and it is not okay….it is not okay at all. I had this happen to one of my own dogs many years ago and it took years for my dog to recover from it. All dogs go through critical fear periods that are very well documented in scholarly literature. The first one occurs between 8 and 11 weeks of age: It is really important not to frighten the puppy during this time, since any traumatic event during this time will have a profound long term effect. Now your pup has the brain wave an adult dog and this is the ideal time to go to his new home. He can now learn the basics of come and sit. Potty training can begin now Housebreaking begins. He now learns by association. He is ready now to start to bond with his human, accept some gentle discipline and develop confidence. Children or animal should not be allowed to hurt or scare the puppy -- either maliciously or inadvertently. It is very important now to introduce other humans, but he must be closely supervised to minimize adverse conditioning. Learning at this age is permanent. If puppies have “bad” or scary experiences during this time, the impressions are likely to last a lifetime and resurface during maturity. So, protect your puppy from these long-term effects by avoiding bad experiences. Should your puppy become afraid for any reason, dangerous or not, immediately step in and remove him/her from the situation. That is good parenting!
Let your dogs meet safe, calm non reactive dogs during this period, so that your dog learns social behaviour from the best that you can find.
The Second Fear impact period (6 - 14 Months): Also called, "The fear of situations period", usually corresponds to growths spurts. This critical age may depend on the size of the dog. The fear period at this stage lasts about one month and can vary depending on the size of the dog. During this time a reactive dog or any other scary event can affect the puppy for the rest of his life. Take great care not to frighten your dog during this period. Soothing tones may serve to validate his fear. His fear should be handled with patience and kindness, and training during this period should put the dog in a position of success, while allowing him to work things out while building self-confidence. Praise during training experiences goes a long way to overcoming fear.