Dogs are a common subject of song. "Old Blue" is a simple song about a dog. It's been done countless times in countless styles. With each version the song changes to suit the performer. It was a popular song with the medicine shows and got passed between musicians and regions, and as it passed it evolved, taking on the local flavor at each stop.
The first recording of "Old Blue" that I am aware of was a blues version by Jim Jackson. Recorded for Victor in Memphis, Tennessee on February 2, 1928, but it was a standard on many musician's playlists by then.
Here are two different takes on the theme.