The book is based on a two-year study done by a team of researchers. University of Kentucky geneticists Gus Cothran and Kathryn Graves, UK pathologist Thomas Swerczek and writer Marianna Haun. According to these researchers, other racing champions identified to have carried large hearts include Man o' War, Count Fleet, Citation, Seattle Slew, Affirmed, Mill Reef, Nijinsky II, Northern Dancer, Native Dancer, Kelso, John Henry, Spectacular Bid, Alysheba, Easy Goer, A.P. Indy, Forty Ninerm and Cigar. A remarkable list indeed. We suggest that differences in heart size may occur in sled dogs as well, similarly affecting racing performance.
Bigger hearts make better athletes, the study reveals.
While the study points out that some great horse racing champions have had normal-sized hearts, the great majority have carried large hearts. The study's important contribution to racing and breeding is showing which stallion lines carry the large-heart gene and how it transmitted from one generation to the next. According to The X Factor , not only is the relationship between inherited heart size and racing performance demonstrated, it is possible to trace the sire lines that have carried the large-heart gene from generation to generation through the broodmares in the family. Again note, it appears the genes for large heart pass on the maternal side of bloodlines in thoroughbred race horses. Stated another way, the research found that certain sire lines that trace to common genetic beginnings carry on the large-heart gene through broodmares.