Actually, horses cannot be 'helpful' in the traditional sense. While an individual horse may be extremely intelligent and sentient as I have found in my experience, however in language we would still view them as animals, and not people.
I think the distinction here is that for the horses to be helpful, they need to initiate the 'helping' of their own volition.
Here, the horses are useful objects, much like a good knife or a screwdriver, neiher of which can be rightfully be called 'helpful'.
No offense to the vegan below - i am one too! :)
Hope this helps.