For what it's worth, my personal vision of "Venus" doesn't include horses, either - they just don't seem to fit the aesthetic landscape, so to speak.
There seems to be an assumption that, though the humans are basically... human, all the fauna and flora is exotic and alien. (However, with the use of some "Earth terms" and some variation on Earth-based lifeforms.)
Dogs, horses, and so forth all seem to be "foreign" to the Venusian environment, in my mind, unless they're meaningfully distinct from their Earth counterparts.
It's an interesting inkblot test of sorts!