And back to Arabs...  For centuries the Arab 
was bred as the ultimate "generalist" saddle horse, and was tough and wiry, and 
had an in-the-tent disposition.  Those Arabs can still be found, and more 
and more breeders are returning to breeding them.  But like most other 
breeds, the show ring has not done the Arabs any favors as saddle horses.  
The halter trend in Arabs has been a long, weak back, excessively long cannons, 
little depth to the body, etc., and disposition has gone out the window in the 
show ring as well, as the trainers prefer to breed horses that only trainers can 
handle (keep one's job going, you know), and unlike the stock breeds, which have 
become beef-on-the-tiny-hoof contests, the Arab halter ring has become a 
who-can-look-the-craziest contest.  So while Arabs still dominate the sport 
of endurance by virtue of the fact that there are still a fair number of 
breeders who have tried to maintain old standards and to heck with the show 
ring, one can't just open up the Classified ads and assume that any Arab there 
will be an endurance prospect, either.  With the long-backed fad in Arabs, 
I've seen a mind-boggling increase in back problems and resulting lamenesses in 
Arabs in the past 20 years vetting rides.  Sad.  So that's one thing 
one needs to take care avoiding in modern Arabs.  And there are 
others.
 
Bottom line--no matter what the breed, you need to 
first educate yourself to the general qualities that it takes to do endurance, 
and then carefully shop within the breed to find those individuals who have 
those qualities.  Yes, your odds are higher with the Arabs, but just 
because the horse is an Arab does not automatically make it an endurance 
prospect.  Nor does the horse become automatically ruled out just because 
he isn't an Arab.  And good endurance horses are often related to each 
other, since both the biomechanical traits and the metabolic traits needed for 
success tend to be heritable--so once you've seen a few related ones of ANY 
breed that do well, you can often shorten your search by seeking out more 
related individuals when you go horse shopping.
 
Heidi (who loves her old-style Arabs, is eternally 
greatful for their wonderful dispositions and athletic capabilities, and has no 
interest in personally riding anything else--but who never ceases to admire a 
GOOD horse of ANY breed or breeding....)