With 400 cards and only 30 kingdom cards, I wonder how the other 70 cards are accounted for. 70 events seems implausible, so maybe Horses are cards, or maybe Ways are implemented in a way that requires a lot of cards.
Well, it's animal themed, so there could be some sort of "super-rat" pile that has 80 copies.
I'm assuming that Ways are Landscape cards (like discussed above, the equivalent of Events for Actions).
When Events, Landmarks, and Projects first came up out there were 20, 21, 20 of those, so 20 seems a safe assumption. Add 10 events (Empires added 13, so <20 seems to make sense), that's 30 of the 70.
The remaining for 40 would then be, like GendoIkari, said, some super sized piles, or also other non supply piles related to the 30 Kingdom cards. (or if one extra pile is only 8, 12 cards for a Victory card pile).
As you can see, I'm assuming that Horses are just the name for card tokens, like Villagers for action tokens, and Coffers for coin tokens.
The question I'm interested in is, assuming that's true, when can you use the Horses? Villagers are only during Action phase, and Coffers only during Buy phase. Will Horses be limited to just one phase? or anytime?
Limiting to Action phase doesn't stop you from using them right *before* your Buy phase to draw extra Treasure. I guess they could be only during cleanup (drawing for your next hand), but that seems way too limiting.