Which Breeds compete in Endurance

In 2005, the American Endurance Ride Conference (AERC) published a table of which horses participating in their endurance rides by breed.  You can find the original report here.
http://www.aerc.org/Membership_Breeds.asp

1810 Painting of Arab horse by Antoine Jon Gros
Source: Wikipedia

Out of the 25716 horses registered, Arabs and Arab crosses (included Morabs etc in this group) dominate this sport representing, respectively, 55% and 14% of the total.  (There was one Fjord-Arab cross and since no other Fjords are represented I did not count this as an Arab cross figuring the Fjords needed the representation.)

Other groupings that were well represented were Appaloosas (700) and Appy Crosses (37), Mustangs including Keigers and Spanish, etc.  (293) and cross (31).

Certain breeds were not heavily represented despite the huge numbers in the US.  Quarter horses (189), Paints (160), Thoroughbreds (315) and crosses (16).

There were 162 mules, 5 Andalusians (no Lusitanos), 1 American Warmblood, 10 Trakenhners, 3 Belgians.

Surprisingly there were many more gaited horses, more than would be expected based on their proportion within overall breed numbers in the US.   Peruvian Paso (48), Kentucky Mountain Horses (8), Missouri Fox Trotters (93), Rocky Mountain (24), Saddlebred (72), Tennessee Walkers (236).

In 2005, there were....drum roll please...16 Icelandics on the AERC roll.  Considering there were probably around 3200 registered Icelandics in the US  at the time, this is a pretty good representation of the breed.