It's rumoured that the female equine can be challenging!
Principal Body System: Reproductive
Definition: The mechanism by which the thread of life is sustained. Organs (ovaries) that produce reproductive cell,s and other organs that transport and store reproductive cells.
Function: Reproduces the organism.
In natural horse-world, mare-ness is completely normal, but for us human caretakers, half a ton of domesticated girl with hormonal attitude can be, shall we say, interesting.