x - Anglo-Arab, xx - Thoroughbred, xfb - Auxiliary Foalbook, xsb - Auxiliary Studbook xxA - Accredited Thoroughbred xx B - Thoroughbred foaled in the Netherlands, xx BB - Thoroughbred not foaled in the Netherlands, xxU - Unaccredited Thoroughbred... (Check
here for reference. The history of the British Thoroughbred, which is the foundation of all other countries related Thoroughbred bloodlines is found here:
http://www.kyhorsepark.com/imh/bw/tbred.html ...
Additionally, according to
Wikipedia and all my desk refernces (we raise Morgan and Quarterhorses) The Thoroughbred is a horse breed developed in 18th century England when English mares were bred with imported Arabian stallions to create a distance racer. As "thoroughbred" is an adjective that describes being fully-blooded descendants of a particular breed, some consider the proper name of this particular breed to be
English Running Horse, as horses of different breeds can be said to be "thoroughbred" members of those breeds. ...
A pedigree is the written or graphical representation of the lineage of the horse. Pedigree's are very important in recording ancestories in order to achieve a given outcome of future generations... especially relating to disease, conformation, color and other desriable and undesirable traits. Check
here for a source we use... Think of it as a family tree.