Well, you'd expect a species that earned the nickname "man's best friend" too be loyal. And boy, are these two little hounds loyal to Billy. Old Dan's loyalty might only be matched by his stubbornness. The thing is, you might as well call this kid "dog's best friend" cause he is one loyal owner. He never leaves his dogs behind, he chops down the biggest tree in the woods for them, and he even swears to lay down his life for them. The sad thing is, they're the ones who end up laying down their lives for him. In Where the Red Fern Grows, loyalty is serious—and deadly—business.
Billy's loyalty to his dogs has nothing to do with Old Dan or Little Ann specifically. It comes from how hard he had to work to get them.
Because Billy's loyalty to his dogs conflicts with his loyalty to his family, it puts Billy in dangerous, sometimes life-threatening positions.