Would be before '51 according to that page. In 1951 they started using the phrase "Bull Dog Beer" on the cans which is on the one to the right of the one you found.
3 Gallon Carboy -
6 Gallon Carboy #1 -
6 Gallon Carboy #2 -
Bottled - Show Mead, Acai Apfelwein, Warm Winds Blond, Vertical Line Pale Ale.
Up next: 2 or 3 different Saisons