This is one of those books that opened my eyes to details of the history of horses I'd never considered. Margaret Derry is a professor who has written some of the few books out there which analyze the way breeds of horses (and cattle, in some of her research) have been modified through time to suit changing needs, and how breeds have been marketed throughout history. In this book she looks in great detail at the concepts of pure breeding, breed registry development, and the marketing of various horse breeds in North America, with special attention to the development of heavy draft breeds at the turn of the 20th century, and a fascinating aside about the changing market for the Arabian horse in the late 20th century US. Here's a brief quote about the Percheron:
The history of the French Percheron shows another way that a 'type' was forced to become a 'breed' in order to meet American demand. French horsemen bred for a heavier style of Percheron and set up a stud book for this stock, not because they found such animals more desirable or believed a stud book improved breeding methods but because Americans wanted heavier horses and proof of 'pure' breeding. .... Purebred breeders also played a disproportionately important role in the entire horse industry and market, probably because the cultural environment of the time defined improved quality in all domestic animals in terms of 'pure' breeding. Heredity, generally, was understood through the effects of purebred breeding, in spite of the rediscovery of Mendel's laws in 1900. (p. 233-234)
This is a detailed, scholarly book, not light reading, but it is a brilliant piece of scholarship, and I'm not aware of anyone else writing on these subjects.