I've also heard of the reference to Parisian women resorting to dogs...I also chased down just about every reference to bestiality when I was younger. And I can't remember what book it was in, either.

As for the soldiers and the cavalry horses "using his horse for another purpose" was a euphemism employed for the practice at some time or another.

A week of internet searching a million dead ends, and two tired blurry eyes, and all I could find was a few thinly veiled references to women substituting animals for their human lovers.....when men were in scarce supply.
If it's on the web........it is certainly hard to find !!