How about THIS for Endurance

[Jeff and Bambi Forbes <forbes@mountainmax.net>]

My sister has an employee from Mongolia, and they were discussing
horses.  The Mongolian Ponies, 12 to 13 hh, were used by Ghengis and his
relatives to conquer vast lands including most of Asia (I guess northern
Siberia wasn't really worth it) and from the edge of what is now Europe
all the way to the Pacific, all from the backs of these tough little
ponies.

They don't feed them anything.  They graze on the tundra plants that
emerge from the permafrost.  They use them for herding, eating (I think
the US is the only country that doesn't) drinking their milk and
racing.  The crazed races have five- to twelve-year-old boys and girls
(lower weight factor), racing at a full gallop for 20 to 40 miles.  If a
child falls off the pony keeps racing (there is no word in Mongol for
"whoa") and they pick up the kids with vehicles.  The ones who really
want the honor of winning toss their saddles off at a lope, to lighten
the load.

So here's the cool part.  During the Vietnam war (so the Mongol employee
says) N. Vietnam, communist like Mongolia, needed horses for agriculture
(and probably for food) so Mongolia sent them a bunch of ponies.  Half
of them died from the heat and humidity and the rest of them WALKED
HOME!!!   Well, they probably trotted, or loped.  Border to border, as
the crow flies, it looks like about 1500 miles.  Talk about barn sour.
And no barn or hay to go home to...

Forget about importing some for Endurance.  The Mongolian Death Trot is
said to be a killer.

Bambi