On second thought I do think I can make a small contribution in this thread - for me, every species we have domesticated indicates a true intermarriage between species. Every food plant, every animal, every fiber plant. The modern conception we have of ourselves, however, is as individual people with separating personalities. And though there is some truth to this, I believe a deeper truth is that we are the limbs of each other's bodies, the organs of the greater organism. And much the same way that a rabbit mother can reabsorb a fetus into her if the nutrients are needed back, I believe horses are both a food animal, a tool animal, and an actual relative, in the same way this is true of the plants in our garden are food, tools, and companions.
I believe for those of indo-european cultural descent (not the fantasy of race or genetic descent, but those who descend culturally from the horse-breeders of the steppe), for many of us we're afflicted by dreams of the horse life. Our daughters (and perhaps less often our sons) seem to come into this world loving horses unbidden. I think these are all clues to the ancient intermarriage that we have to work to circle back on and heal in a particular way.
I've ridden horses before, I don't have a very substantial current relationship with any horses, but I do feel the call at times and these are my thoughts on the matter.