I've heard a lot about the Mongolian Horse over the years, especially that it has more stamina than the Arabian Horse. It's a little smaller/lighter than an Arabian.
Apparently the Mongol Horse can outlast an Arabian, despite having a lower top speed, due to stamina. NOTE: I could not find a good source for this, especially when talking about medieval times. It's very hard to find a true apples-to-apples comparison, because of things like a heavy Knight vs a lightly-armored Mongol, and back then Arabian horses were a little different anyway.
The Mongolian Horse can subsist on grass alone, whereas the Arabian Horse needs a lot of oats if its gonna do heavy hauling or riding.
The Mongolian Horse doesn't need horseshoes, since for some reason the hoof doesn't wear down much over its lifetime.
I would like to know, what biological differences can explain this? Do they have a different kind of muscle? Is their heart or lungs significantly different? Bones?
And the granddaddy point: What percentage difference exists between the DNA of a Mongolian Horse versus an Arabian Horse? For reference, the difference between a human and a chimp is about 1.2% .