where does the quote "strong, like bull." originate from?

Saw this in a 1960's article in reference to Sonny Liston, so it goes
back at least that far.

The earliest reference to "strong, like bull" I was able to find was
in a 1950's sitcom called "Make Room For Daddy"(1), featuring the
actor Hans Conried(2) as Uncle Tonoose.  Conried would later appear on
the Rocky and Bullwinkle show as the voice of Snidley Whiplash.  (This
is important because the most common origin listed of strong like bull
is from the character Boris, and Conried is the most likely reason for
it's appearance in the cartoon.)

Tonoose was known for saying "strong like bull, smart like streetcar"
as a catchphrase.  His first appearance on the show was in 1956.

1. http://www.imdb.com/title/tt0045410/ 
2. http://www.imdb.com/name/nm0175788/

This thing is around quite longer that:

I wish you (to a newlywed boy)

The duration of a dog
The frequency of a sparrow
The strength of a bull

That means bull is considered as strong long back!!