This doesn't make a bit of sense.
One of the most important tools in a farmer's arsenal when dealing with animals is his horse.
I can understand not being able to offer clovers on a raft or boat, but on horseback? C'mon.
For RP purposes, this should be a high priority fix. In a game where everything -tries- to emulate real life, and a lot of the gameplay decisions and processes are founded in "how would this really be done" and the amount of time and effort that obviously goes into research and education before implementation - this seems like a lazy oversight. Like maybe there's some kind of logical/programmatical challenge associated with making it work and it was deemed "not worth it."
It is worth it, and its silly that the game works this way.
The main thing I love about this game is the realism and the attempts to be as lifelike and procedurally accurate as possible.
Animal handlers ride horses, and handle animals on horseback.