This article is from the Dogs Agility FAQ, by J L Gauntt with numerous contributions by others.
Agility trials are open to all dogs, both purebred and mixed breed
(with the exception of those sanctioned by the AKC, which restricts
trials to AKC-registered dogs only) . Dogs of medium build that come
from breeds and/or lines of breeding that have retained their original
working abilities tend to be the most successful in agility
competitions. However, not only does no one breed dominate agility
trials, outstanding individuals of nearly every breed are seen
performing well both in local and national events.
Because of the athletic requirements of the sport, dogs that are less
agile by nature of conforming to the physical structure typical for
their breed are only rarely seen or successful in the forms of the
sport conforming to international rules (USDAA and AAC). These dogs
can be successful however at the domestic forms requiring less actual
physical agility (AKC, UKC and NADAC). This applies primarily to the
larger, giant breeds and to some extent the short-legged, long backed