"Heart" has physical basis


 

This article has been taken from Working Dog Web-Heritage North Press

 

New Discovery Made in Top Racers

Every sled dog driver quickly learns about the term "heart" as it applies to his or her dogs and their individual performance. Some dogs clearly demonstrate that they have something "extra" that allows them to excel on the race trail. When other dogs are flagging, tired and ready to slow down, dogs with "heart" are enduring, able to keep pushing the team onward. They demonstrate this spirit in vivid ways, and often become known as the sparkplug of the team. Some racers equate "heart’ with courage or guts.

Most mushers attribute this quality to a general combination of good physiological traits -- or simply to a dog’s personality -- without thinking much more about it. Few if any mushers consider it a trait they could breed for in any specific or concrete way. Or measure.

Remarkably, however, the concept of "heart" has now been linked in top race horses to the exact physical organ from which the term is derived.

Remarkably, however, the concept of "heart" has now been linked in top race horses to the exact physical organ from which the term is derived. An article in the April 25, 1997 issue of Newsday describes a new book, The X Factor, which explores a critical link between genetics and performance.

The research reported in the book was launched after the discovery that "Secretariat, the standard by which all thoroughbred performance has been measured since 1973, carried a heart estimated during autopsy to weigh 22 pounds - by far the largest blood-pumping, oxygen-distributing organ ever seen in a horse," the Newsday article explains.

In contrast to Secretariat’s 22-pound heart, the average weight of a thoroughbred's heart is 8.5 pounds. Many now believe that the ability of this legendary horse to run farther and faster than any who had come before -- and to win the 1973 Belmont Stakes with a record-shattering 31-length victory -- was based in large part on carrying a heart about 250 percent larger than normal size. 

The book is based on a two-year study done by a team of researchers. The members include equine cardiologist Frederick Fregin, director of the Marion duPont Scott Equine Medical Center in Leesburg, Va.; 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.

...differences in heart size may occur in sled dogs as well, similarly affecting racing performance.

Some call this work "one of the most important research projects ever undertaken in the area of equine genetics and racing performance," according to Newsday. We suggest that differences in heart size may occur in sled dogs as well, similarly affecting racing performance.

Why Big Hearts Matter

A large heart offers an obvious advantage: it sends more blood and thus more oxygen to the muscles, giving the animal greater endurance and more capacity for exercise. 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.

Tracing the Big Heart Gene 

What exactly did the research find that would allow it to be applied to breeding? 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. This discovery "leaves the distinct impression that the maternal lineage may be more important than the paternal side of a pedigree," the Newsday article states. 

In summary, using historical knowledge of great horses and new data collected from present champions, the researchers applied the principals of modern genetics to demonstrate that large hearts are "predictably inheritable" and identified which race horse families carry the large-heart gene.

Putting the Research Results to Work 

Horse experts evaluating the ideas presented in The X Factor suggest the findings will have an impact on selection of studs and mares for mating, and also change the way yearlings and 2-year-olds are evaluated. "After correctness of conformation, heart size may become the second-most-important ingredient considered by those preparing to spend serious money on untested horses," the Newsday article states.

A big heart "will not make legs more sound nor the stride more efficient. It does not carry courage, will or the determination common to all great horses. It will simply provide a larger supply of blood and oxygen to the muscles," the Newsday article asserts. Nonetheless, this trait is found in the majority of modern champions and might well be shown to be true of all successful horses at various levels of racing. 

One immediate application may be the method outlined in the book for determining a "heart score," a figure that may one day be included in sales catalogs and performance charts for race horses. How interesting if this same trait could be conclusively shown for racing Siberians, a concrete measure to breed for!

-- Barbara Petura, Editor, WorkingDogWeb


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