Join Date: Aug 2009
Location: New South Wales, Australia
Appendix isn't a breed, not really, which is probably why there is the confusion. There is no "Appendix" breed registry or anything. These horses are registered with the Quarter Horse Association so if anything I'd refer to them as Appendix Quarter Horses. The word "appendix" literally means basically an "additional section/list". So an appendix is a horse that isn't eligible for the regular registry, but can be registered on the "appendix" list. In the case of QHs only the progeny of registered Thoroughbreds crossed with registered Quarter Horses can make the appendix list (to my knowledge). There will be different rules for these horses, and they may be able to be bred back to QHs, or perhaps not.
Many breed registries have this. Like if you cross a Paint and a TB and get a solid foal its called "Paint Bred" and it has it's own classification. The Australian Stock Horses Society has registrable "First Cross" horses.
Without being registered with these associations the horse is not a Paintbred or Appendix, its just a QHxTB or PaintxTB etc.