Why is my dog attacking my older dog all of a sudden?

The most common reason why a dog is suddenly aggressive toward another dog from the same household is a dispute over one of three things: Possessions, Food, Space / Territory. All three can be managed provided the problem is addressed promptly. Intact male dogs tend to have more innate aggression than either female dogs or neutered males. However, this is certainly no guarantee. Aggression - including sudden aggression - can come from old dogs, young dogs, female to male, and male to female. If you have a dog that is suddenly aggressive to another dog in your own home you need to establish the exact trigger point. Look for the following: Aggression related to food or toys, Aggression related to jealousy, Aggression related to fear, Aggression related to space/territory. Underlying health concerns can often manifest as sudden changes in behavior, including aggression. Once any medical issues have been ruled out, get the view of a dog training expert who can help you deal with this stressful event.

Hilda has always been very submissive especially to my parents large group of dogs, but today resource guarded the bed and went after 3 of their dogs in succession over the space. She’s never had any problem with any of the three dogs. I’m wondering if I should be considering a medical issue since this progressed so quickly. It’s barely been 6 weeks since a little toy scuffle, and now she’s gone from sweet, more submissive, agreeable pup to unpredictable and possibly violent at an alarmingly increasing rate. We just went to Disney, and got a call from my sister who Hilda is staying with now. Hilda stayed in my parents house with a bunch of other dogs and lots of regular house attention, Zena went to a board and train where she made leaps and bounds in progress. We come back, Hilda goes after Zena when Zena tries to sit next to Hilda and I on the couch. We separate, carefully reintroduce again, move on. 3 days later, Hilda goes after Zena seemingly unprovoked when Zena comes in the room with all of us.