Holy shit... I'm not a leg man but... OMG it just hit me, this lovely equine creature looks like it has two coochies.
That's a standard part of the fetish. And the boytaurs (male versions) have (at least) two wieners. The fetish usually extends out to more than just two sets of legs into a sort of human centipede, non-scatalogical version, and sometimes goes along with multiples sets of arms as well.