didnt see this in search.

On a PC here and have had 2 giant quests buggered up.
Both times, I get to different camps, I see giants, but my quest marker is on a stag running around in camp, who then runs from me.
Have to chase and knock it down with voice, then chop it up. Quest finishes.

I reloaded once to see, same thing happened, with the quest giant, but also, another giant in camp was a stag. They also act like stags(in that they run away) so it is not just the graphic.
I have a few mods installed, but nothing that I thought would have done that.

Not sure where horses come into this, but save a game, exit, restart and disable the mods. Then see. You'll have to enable them one-by-one to see which one is dirty.

yep, sorry about that, should have been deer

It's always the mods. Especially if you have not updated them for the latest patches.

If you have a lot of mods, better to disable half of them and see if the problem persists. If it does, disable half again (now running 25% of your mods). Continue this process until you identify the problem mod.

If you disable half your mods and the problem does not persist, the problem mod is in the inactive half. Activate the "other" half and continue the process.