Yeah, zebras seem like one that there is a lot of good and bad examples of mixes. The trends for this one aren't even that clear either, as oftentimes a mix that works in one place may completely fall apart somewhere else, or even with different individuals. Really I think Plains Zebra are one of the few species that too many zoos keep anyways, so I wouldn't mind seeing some zoos phase out zebras altogether, with some keeping mountain zebras in "safer" mixes (giraffe, white rhino, and ostrich come to mind).