We are talking about nipping and growling. If the dog is in serious pain, then yes, nipping and snapping and growling COULD be the issue with this dog.
So far, I have not heard of any biting? Has this dog bitten a child?
How old is your niece that he is growling at. What are the circumstances. Before we suggest euthanasia for aggression, let's figure out what we are dealing with.
In a shelter this dog would be put down most likely for the hips issue, or for the aggressiveness. Why? Because there are a lot of pups whose only issue is having lived too many days at the county's expense, to waste resources on a dog that is not a good candidate for adoption. It makes sense. Less liability too. And the more shelter dogs that have high vet bills, or aggressive incidents, the worse the reputation of shelter/rescue dogs, and the less chance for any to gain a forever home.
But, this is a dog that the OP has owned and loved for almost a year now. If she can find it a good home, that is great. But if not, let's look at how much aggressiveness there is, and whether there are any options when it comes to getting the dog the care he needs.
Again, the skin-kids are first, even the niece so long as the niece isn't doing something that is scary or possibly painful to the dog. And it is totally understandable if the OP finds she must put the dog down.
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