In studying this morning we realized that it may be a bit more suitable to refer to unclean animals as unfit animals. The Hebrew word here is tamei and carries the meaning of not permissible to eat.
When we look at a horse and a goat we see that the horse looks just as "clean" as the goat; or maybe even more so (lol). However, just because the horse looks clean does not mean he is tahor (fit to eat). Yahweh has declared the horse as being unfit, not necessarily unclean.
Either way the message is the same; just a thought for this fine morning.
EMJ