"Heart" has physical basis
New Discovery Made in Top Racers
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 dogs 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
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 Secretariats 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
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
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
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
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,
at Racing Siberian Husky Online
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