I really don’t know where you are going with this. They don’t go out eating plastics and whatever either. They get sick because they’ve eaten something contaminated (what happens way more often on the wild) or because they failed to distinguish the food (what also happens way more often on the wild).
There is lots and lots of “unwanted” food that will kill a horse in most natural habitats through the world.
Which they’ll instinctively not eat
I really don’t know where you are going with this. They don’t go out eating plastics and whatever either. They get sick because they’ve eaten something contaminated (what happens way more often on the wild) or because they failed to distinguish the food (what also happens way more often on the wild).