I don't know if @DaPorkchop_@lemmy.ml intended it when they said "Horse girl", but pregnant horse piss, was one of the first feminizing HRTs, both in ancient Roman Transfem sects, and in the 1960s (the Premarin pills).

So... The evolution of the Horse girl... Keeping a cis girl to harvest estrogen from her...

There's a pretty good bad joke somewhere in there.

Keep in mind, said Horse girl needs to be pregnant as much as possible, to maximize the availability of estrogens in her body.

Make of that what you will.