Rebellious dog

A story for young people, telling the life of a pasture dog, from the time he was a small puppy until he became a huge, fat dog, characterized by strength, courage, and loyalty, until all the other animals feared him and the livestock obeyed him, and he became his owner's favorite dog. But a tragic incident changes his fate forever, and the view on him shifts from one extreme to the other. What is this incident? How did you turn him from a loyal dog into a rebellious dog?