Well I can tell you with ~60UA they still punch through 1 whole defense move. I recommend using a hirdsman sword and just punch it 4-5 times without defenses up and then just chop it. Btw I have like 75agi and the horse is still pretty fast.
Horses are the easiest animal to hunt after rabbits and chickens, you just have to think a bit
Make a small trap out of branch stockpiles, then when you find a horse feed him a clover and ride him into the trap, close it with one final stockpile and thats it you can shoot him to death at your leisure.