(G) Well, I had an old dog and his (C) name was (G) Blue,
Had an old dog and his (D) name was (G) Blue.
Had an old dog and his (C) name was (G) Blue...
Betcha five dollars he's a (D) good dog (G) too...
"Here old Blue"
(D) "Good dog (G) you"

Some other folks may have slightly different chords--and you can use a D7 where the D is. Hopes that's accurate. I have never played the song, but those chords sound right--or jus' about.