twenty one horses - nice photo
This source says that the horse population in the U.S. peaked at over 26.5 million in 1915 and had declined to 7.6 million by 1950.
Wow Mark, people sure had to deal with a whole lot more "horse crap" in 1915 then in 1950.
That's why automobiles were initially considered a godsend to the environment. People (particularly in the big cities) were up to their ankles in road apples! Cars don't leave road apples.