Many old blues songs deal with canines - metaphorical Hound Dogs or actual dogs. The most moving old dog song I know is Jim Jackson's Old Dog Blue, which is very similar to the traditional bluegrass song Old Blue.
The country blues blog Done Gone has a nice article about the song with lyrics and a recording from - what year? I'd like to know. Jim Jackson sings and picks beautifully, mournfully.
I had an old dog whose name was Blue
You know that Blue was mighty true
You know Blue was a good old dog
Blue treed a ‘possum in a hollow log
You know from that he’s a good old dog
The lyrics convey the pride of the hunter, missing his prize hound, but there's something more to the story.
Blue treed a ‘possum out on a limb