Horses, my sources inform me, are crap. Horse people may be able to provide more nuance here.
Grass isn't good enough for them. If they eat an all-grass diet they starve.
They need oats, a high-calorie food.
This is famously a problem in military logistics. The animals you're using to move the food eat the food.
But if you leave horses alone with oats, they'll overeat, and they can die of it.
When I first heard this, from a vet, my reaction was incredulity. It's a priori ridiculous. How on earth could such an animal evolve?
Think about it.
No really, think about it. How can horses exist? Write down your answer before proceeding.
The answer, of course, is that horses didn't evolve naturally.
Steppe ponies, and the other equids that are naturally evolved animals, can live on the food available to them, and they have proper appetite control and neither over- nor under-eat, effortlessly maintaining their optimal body weight in good conditions, without using willpower.
Horses are the descendants of such animals, but they are far from natural creatures.
We created them by long-term selective breeding, and we've always been around to provide the oats, and to make sure that they didn't over-eat.
We've never bothered trying to breed them for proper appetite control. It would be a nice to have, but it's never been worth the effort short term.
Horses live if and only if humans are looking after them.
So far so good, but today I was pontificating about this, and a young friend came up with a stunning question:
"Oh yeah, so how come there were wild horse herds in North America? The Red Indians tamed them and used them for war."
I don't know the answer. Write down your answer now, and then go and find out.
Weren't the horses the native americans have from the spanish/European settlers in South America. There were equids on the continent but they may have died out thousands of years before, they may have been a victim of the younger dryas event which may have killed off the large fauna of the americas.
> Evolutionary Reasoning is Harder Than It Looks
Evolutionary reasoning is mostly fantasy, which is why I avoid it.
Example:
It is really useful to be able to fly. Why would nature be so stupid as to not give humans the ability to fly? Nature doesn't make mistakes! Are you saying evolution isn't true?
Therefore, clearly, humans can fly.
This is the average level of discourse of evolutionary reasoning in nutrition.