Aggressive behavior from formerly docile dog

[Animalhouse26]

a behavior like this that is So out of the norm.. would call for a vet visit Good luck, I hope all is well!

[Dixieland Dancer]

There are so many possibilities for this "new" behavior. First off... In a house with 6 other smaller breed dogs, why would you NOT have Mack neutered already? Rottie's are loving dogs but they are also physically and emotionally strong dogs. Neutering has strong benefits if it is done at an approptiate age. After the fact the behaviors are learned and it has less of an impact but can still reap rewards in hormonal issues. I am assuming Mack is somewhere around 1 year to 1 1/2 years since you have had him for about 7 months and it sounds like you rescued him. If that is the case, it is still a beneficial idea to have him neutered. His age in and of it's self could explain the change. He could be going through his adolescents and it could be hormonal.

I will say though that I do not know enough from what you wrote to know for sure what is going on and I strongly suggest you do get a dog trainer who has a behavior issues background involve ASAP. From what you do write, I do not lean towards hormonal but more of a reflex response. Since it is only directed at the Bostons, I would think that something happened that you are not aware of that is causing the sudden change in the Rot's behavior.

In any case, you need advise from someone who can see the interaction of the two dogs in question so they can give a more educated analysis of the situation after seeing the dogs interact.

BTW.... I don't know of ANY vet that would want to put a dog down for this kind of behavior unless it was totally out of control and the aggression was constant. If your vet thinks this way, I would seriously look for another vet. Especially if they make this kind of determination just from a phone consult and not seeing the dog in person.