My gripe with Stivers is that he can't draw a horse properly to save his life (he also has trouble drawing a 19th-century woman, but that's common with 'action' artists).
His worst examples are face-on view. Look at the RH leg of the horse on the far right. Nightmare.
He needs to do like George Stubbs and visit a slaughterhouse and make careful sketches, or if he can't stomach that, hire himself out to groom a couple hundred of them.
He told me that he bought a fiberglass horse and had it installed in his back yard. I suppose that helped with the anatomy and proportions, but not so much with the articulation.
I don’t think that he would have cared much for mucking stalls.