Where did the expression until the last dog is hung originate?

My Grandfather used this phrase frequently. When I was a young boy I asked him what it meant. He told me that once or twice a year the mountain people would cull out their worthless dogs and have a get together at night in the woods and hang the dogs that were not worth their feed. Some men left early because they could not stand to watch the Horror. But it was a badge of honor to "stay until the last dog was hung"

I have never seen collaboration of this explanation anywhere, but it is what comes to my mind when I use the term.