“More horses’ asses than horses”

It’s been said that at the racetrack there are “more horses’ asses than horses.” The phrase applies to many other situations as well and is of unknown origin. Some websites have this as a phrase of Watergate (1970s) figure Gordon Liddy, but “more horses’ asses than horses” is surely much older.
 
   
Down Home-isms (Free Republic)
My grandfather used to use animals in his saws:
 
“That dog won’t hunt.”
“There’s more horses’ asses than there are horses.”
And
“All cats are grey in the dark.”
 
I didn’t figure out the meaning of the last until I was much older, of course.
Posted on 02/28/2001 19:24:03 PST by Snake65        
 
Charade’s Quote Collection
Why is it that there are so many more horses’ asses than there are horses?
- Gordon Liddy  

Freeware Hall of Fame
WATMHATTAH Why are there more horses asses than there are horses
 
13 March 1976, Los Angeles Times, pg. C3:
Reading once more of the egotistic, self-centered Mike Marshall and his latest tantrum brings to mind the old proverb, “There are more horses’ asses than horses.”
FERD CARUANA
Los Angeles
 
4 November 1979, Chicago Tribune, pg. G12:
There are more horses’ asses in this world than there are horses.
Liz McFadden, Buffalo Grove