The following references and resources are some I have found helpful and interesting for the study and understanding of pedigrees, sport breed history and horse genetics. Quite a few of these books and websites are Thoroughbred oriented, but don't let that deter you. You will find that because of the size and health of the racing industry, that they are leading the way in horse breeding, genetics and pedigree reseach. We can be grateful for all the work they have done and then be brilliant and use what they have learned for our own breeding programs.
Below will be websites I have found useful. For genetic study references and for a bibliography of books and articles I have used the links for a pdf version you can print out for your own information.
American Morgan Horse Association
Saddlebred sport horses
Anne Peters-Thoroughbred Pedigree Expert
Sport Horse Data This is a wonderful resource site for the sport horse breeder, loaded with thousands of pedigrees and added to daily--much more accurate than a the pedigree database site especially in the older lines.
Equine Post- great source of information for all breeders
Ellen Parker- Thoroughbred Pedigree Expert
Horse Genome Project
Nickolas Matsza's Breeding Trotters
Thoroughbred Heritage --good overall resource, however the jumping lines articles do not consider the American lines--definitely biased to European warmblood point of view