The X Factor: What It Is & How to Find It: the Relationship Between Inherited Heart Size and Racing Performance

Scientists have known for years that superior human athletes have hearts that are substantially larger than those of non-athletes. Human athletes can increase the size of their hearts through proper conditioning. Scientific research shows that superior racehorses, both Thoroughbreds and Standardbreds, also have hearts substantially larger than those of average horses. Unlike humans, the size of equine hearts is an inherited trait. Large racehorse hearts are passed from generation to generation along the X chromosome, through the mare. The challenge faced by breeders and buyers is learning how to capitalize on this important research. Marianna Haun was part of the U.S. team that conducted this ground-breaking research. In her book, The X Factor: The Relationship Between Inherited Heart Size and Racing Performance, she explains the significance of Thoroughbred and Standardbred heart scores and why those scores should be considered when buying or breeding a racehorse. Haun identifies the large-heart lines in the pedigrees of champion racehorses and shows how to find it in the pedigrees of horses that haven't yet been examined. After reading The X Factor, you will understand how heart size is measured and what the scores mean. You will learn how to trace large hearts through modern-day pedigrees and be able to find these genetic links in the horses you buy or breed. You will also see the body types that are consistent with large-hearted bloodlines that can be recognized and used in the selection of bloodstock. This is information you can use today to give your racing and breeding program the edge.