I think you may also mean sickle-hocked? Then again, cow hocks aren't desired in reining because the back legs of a severely cow hocked horse would tend to splay outwards in a sliding stop. Other disciplines would find strength in the cowed hock. My stallion is slightly sickle hocked and it suits cutting because he really gets underneath himself. That does mean that he puts more pressure on his hock joint, but he can get really low.