Foundation bloodstock or foundation stock are horses that are the progenitor, or foundation, of a new horse breed or a given bloodline within a breed. The term is also used in a similar manner when discussing purebred dogs. A group of animals collectively may be referred to as foundation bloodstock when one breed, or group of breeds, provides the underlying genetic base for a new breed. This is particularly common in older breeds where a written stud book was not created until after the breed phenotype was well-established.