Definitely against horses need to be fed. I'm a conqueror seeking wars and diplomacy, I don't have time to start micro-managing my horses. It will become tedious and waste time that could otherwise be invested in other, more crucial or fun parts of the game. However subjective that is, should the community for some bizarre reason desire this, they can add a 'hardmode' where you have to feed your horses and other increased difficulty ratings for people who have spare time and love to torture themselves.