Carol Emshwiller's
The Mount. I can't do justice to this in a brief compass but I was sort of astonished to not really like it. My main problems were that it (1) was too science fictional and engaged the logic centers too much to be as illogical as it was and was far too literal to interpret on a purely metaphorical basis though that was largely what it was "really" about; (2) had a standard sort of plot skeleton (revolt against alien invader overlords) that permits little waffling and requires one of a couple of endings and was filled with waffling and had a third ending; and (3) was entirely too humane and enlightened for my taste.
It was very similar in many ways to the fantastical, allegorical, picaresque
Carmen Dog and basically inferior to it - that book avoided engaging the logic centers too much, wandered charmingly, and could end any way it wanted to and did so very imaginatively. Basically, Emshwiller seemed to want to tell a similar story but, this time, wanted to put various obstacles in her way as a writerly challenge. She usually leaps such obstacles with an easy genius but I think they tripped her up here. (Yes, this is a horse metaphor - or a hurdler metaphor, but I'm thinking horses.)
Aside from these problems and a couple of slighter, more specific glitches, it wasn't a
bad book, though, and I can imagine it having been great and may well strike most readers that way, especially if my three main problems aren't problems for those readers.
Anyway: aliens have crash landed and taken over the earth and they have deficient legs and superior senses, so somehow breed a couple of separate lines of humans in a single generation to use as mounts. And erase our cities and civilization and make us all forget everything we'd accomplished except how to whistle a few nursery rhymes, apparently. Our story concerns Charley (Charley... Horse? Heh...
groan), an 11-13 year-old boy whose dream is to be the best mount he can be and whose job will be to carry the grand poobah of the aliens around although he's just a little poobah when the story begins. They love each other but Charley's dad doesn't love the aliens, and liberates Charley from the alien town where Charley sleeps in a stall and gets trained. Charley saves the poobah and we dither over loyalties and Charley's dad's folks wander towards further revolt. This is a book where you can use words like "marshal forces to revolt against the alien invaders" and they're all technically accurate but connotatively useless because that's not what the book
feels like at all. But that's about the non-spoilery synopsis of it.