Muzzling is usually counter-productive.
Quite often, a dog bites from fear rather than aggression and removing his means of defense makes him even more insecure and paranoid.
I tried to explain this to a dumb ass with a clearly terrified, muzzled Pit and even showed her how great her dog could be when -properly- handled and she was in awe of what wonders I achieved with him in just 10 minutes.
And then she slapped the muzzle right back on him because the PetCo “dog trainer” said she should.
And the poor dog started shaking and growling again, just like he had been, before.
If I had to bet, I’d say he’s probably dead by now.
The OP’s sister -must- get the dog a blood panel done; or at *least* a full T3/T4 thyroid panel.
90% of Dobes will get thyroid issues at some point in their life.
It’s only a matter of the degree.
Thanks good points. I only advised muzzling because the dog has become aggressive with no clear predictors of when he will bite. I don’t like muzzling either but seemed one way to keep the dog around people for now. I do agree if the dog objects to being muzzled it should not be forced as that can be another stressor leading to more behavior problems.
I think you are on the mark about thyroid especially because of the rather sudden onset of aggression. Even if it does turn out to be a medical problem I think contacting an animal behaviorist would be helpful.
I know what you mean about people being astonished that their dog can listen and do as told. I’m always amazed that people find that unusual.