If you aim right,you can 1h most of the horses tho.
I remember once while i am riding my champ sarranid horse to a noob looking thrower,then he threw a dagger on my horses head.That dagger took it's full hp and killed my lil poor pony

I don't understand why people are still whining about horse.This is the most ridiculous idea ever btw.If you can kill it,kill it.
If you can't , run away or try blocking down o.O