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Since the earliest days of horse racing enthusiasts have talked about horses with great hearts. Horses who have stood out dramatically from their fellows – who run not only faster, but harder, who never give up until the finish line. It did not refer to a clear-cut physical characteristic, but to a quality of spirit. Imagine then, the surprise when the autopsy on the English racehorse Eclipse – one of the most famous horses of all time – showed him to have a heart more than twice the normal size. An average racehorse of that era had a heart weighing around six pounds; Eclipse’s heart weighed fourteen.
Two hundred years later when the Triple Crown winner Secretariat was autopsied, his heart was estimated at an astonishing twenty-two pounds. For comparison the average modern Thoroughbred has a heart weighing eight and a half pounds. Indeed, many of the greatest racehorses of all time: Man o’War, Phar Lap, War Admiral, Citation, and Seattle Slew, among others, are believed to have substantially larger than normal hearts. Great-hearted has ceased to be a metaphor, and become a physiological fact – and one which may explain some of the mysteries of Thoroughbred breeding.
As early as the 1960’s, Australian researchers were beginning to study the hearts of Thoroughbreds, and to correlate heart size with performance. They found a strong, positive correlation. They also began to believe that there was a single gene, probably sex-linked, that produced horses with unusually large hearts. However, when they tried to relate their conclusions to US veterinarians, they were ignored or ridiculed because they had no idea where the trait had originated, nor could they point out with any reliability which living horses were likely to have large hearts.
Things have changed a little since then. For one thing, many more Thoroughbreds (as well as Standardbreds and Quarter Horses, which also show the trait) have been found to have large hearts, and their pedigrees have been examined in detail to trace back the common ancestry. For another, there is now a means of estimating the heart size of a living horse. Dr. James Steel, an Australian researcher created the Heart Score, a scale that correlates heart weight, stroke volume, cardiac output, and aerobic power. Using the score,
researchers can determine with some degree of certainty whether a living horse has a small, normal, or large heart. Larger scores correlate with larger hearts with the break points between normal and large hearts considered to be 117 for females and 120 for males. Using the data from known large hearted horses, and from over 400 horses measured by a team at the University of Kentucky, the large hearted gene has been tracked through the female lines all the way back to the daughters of Eclipse. Those daughters and their descendants were shipped all over the world, spreading the large hearted X-chromosome throughout the Thoroughbred world. Eclipse himself may be the originator of the large hearted gene in the Thoroughbred line.
The X-linking of the large-hearted gene also explains one of the most frustrating facets of Thoroughbred breeding. Over and over again, wonderful racehorses would fail to sire wonderful racers. In particular, many sires were known for throwing good daughters, but only mediocre sons. Since a colt only receives one X-chromosome, and that from his dam, a large hearted stallion would have no particular advantage in his sons. His daughters, on the other hand, would always inherit his large hearted gene. A mare with a large hearted sire might, or might not, have a large heart herself, depending on which X-chromosome she expresses, but she will carry the gene, and may pass it on to her offspring. So ironically, the stallions known for being great sires were those whose owners chose the mares carefully, with the stallion receiving credit for the mare’s contribution.
Large hearts can potentially have a tremendous impact on earnings. In a study of Standardbreds (trotters) by Nielsen and Vibe-Petersen of the Royal Veterinary and Agricultural University of Copenhagen, the 41 stallions with heart scores above 115 earned more than twice the amount of the 81 stallions with heart scores under 115. One can only assume that a study of Thoroughbreds would likely show similar results.
Obviously the large heart is not everything in a racehorse. Poor condition, unsound legs, or a bad temperament can undo any racer, large hearted or not. But all other things being equal, a large heart can make the difference between a good horse and a great one. With all the new information on the advantages of the large heart, and the new pedigree and inheritance information, the discussions of racehorses with great heart is likely to take on a whole new meaning.
Further Reading:
AQJ article on large hearted inheritance
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Didn’t I read that Lance Armstrong has an amazingly large heart? I think the article passed it off as ‘conditioning’ but what if it is….hereditary? Jim Fixx died of heart failure, just like males in his bloodline before him, in spite of being a big time runner (and author about running), so genetics must play an important part of endurance and lots of aspects of athleticism. Sounds to me like this spells the end to Stud Farms upon retirement…another dream busted!!!!
I wonder if this works the same for humans….
Do the horses with large hearts have more problems than horses without large hearts? I would think that having a larger-than-normal heart would cause health problems for the horse.
And like Hayley said, is this only in horses? Or can it be found in other animals as well?
Interesting article!
Is heart size posted anywhere before a race?…would be interesting to know how much this article could impact the horse racing scene. Data from the past doesn’t always predict the future, but it’s better than let’s say Uncle Joe’s gut telling me how to spend my money. Any horse betters out there who know this?
I have heard of large hearted humans, however these were general autopsies and did not mention the occupation or fitness of the cadaver.
However I do remember reading that one of the males with an unusually large heart died of a heart attack. But with just one case this certainly doesn’t indicate any relation between large hearts and being at greater risk of heart disease etc.
Sorry but I can’t remember where I read this info…
An enlarged heart in humans generally is a form of heart disease. It would be different if a person were born with an enlarged heart but i’ve never heard of anything varying like the horses in this article. In a person the heart stretches out and becomes a flabby-walled sac in one of the two type of enlarged hearts. The heart may also be enlarged because the walls thicken and the outside dimension increases. Inside a thick-walled heart, there’s less room for blood. This type of heart disease can cause a blood clot that blocks the blood flow to the legs and causes paralysis. Obesity is often a cause of an enlarged heart… the body is larger which requires the heart to get larger to pump the larger quantities of blood. I know that other animals can get enlarged hearts, but, again, I’m not sure if they are naturally born with larger hearts. If they were born with them, I would assume they would be of normal blood capacity or greater which would mean it would be pumping larger quantities of blood throughout the body which in turn means more oxygen getting into the animals system.
Thats pretty cool that most large hearted horse’s are descendents of Eclipse.
There’s a difference between a enlarged heart and a large heart.
ballaerina said: “Do the horses with large hearts have more problems than horses without large hearts? I would think that having a larger-than-normal heart would cause health problems for the horse.
And like Hayley said, is this only in horses? Or can it be found in other animals as well?”
Heart size is variable for all animals. Race horses have been bred specifically for racing. With such an intense selection pressure, they acquire a lot of traits that cause problems. Thoroughbreds have a much shorter life span than most horses, and physiologically they’re very different. Just looking at the article, the average heart size has increased by 42% over 200 years. That’s flat out disgusting in evolutionary terms. Some of it may be due to the massive amounts of steroids and growth hormone every race horse receives though.
cornerpocket said: “Didn’t I read that Lance Armstrong has an amazingly large heart? I think the article passed it off as ‘conditioning’ but what if it is….hereditary? Jim Fixx died of heart failure, just like males in his bloodline before him, in spite of being a big time runner (and author about running), so genetics must play an important part of endurance and lots of aspects of athleticism. Sounds to me like this spells the end to Stud Farms upon retirement…another dream busted!!!!”
I’ve heard Armstrong has a resting heart rate in the 30s. You don’t get that from training alone – genetics plays a very large part. Elite atheletes have VO2 Max (rate of oxygen utilization) of 70 or more. An average person, with several years of training might be able to bring it up to 50. To become a winner amongst such a huge pool, you gotta have the perfect intersection of genetics, mental determination, and training.
However, it’s probably the later two that hold most people back since very few people are anywhere near their genetic potential.
I did see a program on the large heart and the fact that they do these tests to determine whether he is a “winner” and worthy of bringing in the REALLY big bucks when they are used to stud. MILLIONS!
I live in the heart of Thoroughbred country…Lexington, KY. I have seen some of the data from these studies first-hand. It is an impressive fact.
I also read or heard the story of Lance Armstrong. I agree that heredity does play a factor, but also years of training helped him be the athlete that he is. If one has a larger heart than normal, but does not train or concentrate on his sport to be the best athlete possible, then the genetic advantage is moot.
I find the X and Y heredity stuff very interesting. Racehorse studs often get reputations as being a “sire of sires” or as a “broodmare sire”. This provides a simple, reasonable explanation. (Since this is genetics, the explanation is probably too simplistic.)
The damn interesting thing is that the horses in the pictures have one leg of a different color.
??? Are we saying that one of Lance Armstrong’s ancestors was a mare???
dmwit said: “The damn interesting thing is that the horses in the pictures have one leg of a different color.”
It is pretty common for a horse to have white feet or “stockings”. There are old folk-loric myths about the number of stockings and how good the horse was supposed to be. Of course the folk-lore was contradictory, depending on who was doing the telling. Some said that the more white legs a horse had, the worse he would be. By the picture, Secretariat with 3, should be pulling a milk cart. (He was perhaps the greatest racehorse of all time.)
The origin of the white feet=bad horse stems from white hooves being somewhat less hard than dark hooves, and so slightly more prone to splitting or other problems. “Three white feet, and a white nose, cut off his head, and give him to the crows,” was the old rhyme on the subject. Obviously, given Secretariat, it’s not exactly a good measure.
Rush said: “??? Are we saying that one of Lance Armstrong’s ancestors was a mare???”
I think we are saying Lance’s legs are different colors.
There is a really interesting book called “The X Factor”, written by Marianna Haun. It does a great job of explaining the relationship between inherited heart size and racing performance in Throughbreds. Chapter 3 is also about Human Athletes and their large hearts…Which can be large to start with, but then are enlarged through training/conditioning etc. It’s a very interesting book
I’d like to add that the November 2004 issue (# 325) of Equus magazine contains an article on this, and a lot more detail. That article explains the elctrocardiograms, how they measure with astounding accuracy the size of a horses heart. There’s also a lot more on specific examples, the genetics of it all, lots of statistics and all that jazz.
donlaudanny said: “Race horses have been bred specifically for racing. With such an intense selection pressure, they acquire a lot of traits that cause problems. Thoroughbreds have a much shorter life span than most horses, and physiologically they’re very different. Just looking at the article, the average heart size has increased by 42% over 200 years. That’s flat out disgusting in evolutionary terms. Some of it may be due to the massive amounts of steroids and growth hormone every race horse receives though.”
Having spent the past 30 years working with thoroughbreds, I felt compelled to dispute three unfounded assertions. Horses are routinely “retired” after their breeding days are over, and often live 25-30 years, more than average for the species. While steroids and growth hormones use does occur in racing stables, it is not universal. That said, the judicious use of either can be benificial in some instances. The racehorse trainer and owner have a great deal invested in their charges, both finacially and emotionally, and the majority do everything they can to endure the long term health and well being of their horses.
I am not sure I understand the assertion that “heart size has increased by 42% over 200 years. That’s flat out disgusting in evolutionary terms”. In the bell curve distribution of heart size in the thoroughbred population, those individuals with an elite athletes cardiovascular system are at the outer edges of the curve, aand are not represented by the average thoroughbred. Even then it is but one factor, (albeit very significant) in what makes up the horse capable of competing at the highest level of racing.
I’m surprised that racehorses live so long. As a biologist, it’s widely understood that growth hormone accelerates aging. Larger dogs die sooner than smaller dogs, and larger individuals tend to die sooner than smaller individuals from age related causes in the same species. Thoroughbreds definitely fit in on the larger side of the curve. From what my jockey friend has told me, horses are typically considered old past 10 yrs. Understandably, racehorses will likely receive better care due to the nature of their owners and may be allowed to live past the point where draft horses are put down. But if what you say is true, then I retract my statement.
About the steroids/GH statement. I have never seen a source besides you mention that it is NOT universal in racing. Of course steroids are beneficial, if they weren’t, then they wouldn’t be taken! Steroids and GH speed up recovery rates and can heal microinjuries that would otherwise result in serious problems. But GH does increase heart size, so part of the 42% increase might come from GH use rather than selection forces.
The 42% were taken from the 6 lbs and 8.5 lbs given in the article. If that’s not true, then the statistic won’t hold. That doesn’t change the fact that the rate of change in thoroughbreds is astonishingly fast. It’s SUPPOSED to be. That’s what artificial selection (breeding and pedigrees) is.
The way a thoroughbred is engineered IS very different. If you look at the VO2 max as well as the oxygen dissasociation curves, you find conditions which are very much outside the regular mamillian physiological range. One example is that their lungs are horribly underengineered for the amount of oxygen that the rest of the system can utilize. This is because races are relatively short and lung capacity doesn’t matter as much, so the selection pressure for the rest of the system, from the cardiovascular to the muscles have been much greater. It doesn’t matter if the lungs bleed, as long as the horse wins the race and has time to recover before the next one.
It’s a little curious to me that in the last 200 years the average thoroughbred heart size has increased 42% but the average speed of the horses has varied within a range of less than 15% in the last hundred years ( I could not find 200 years worth of time and speed statistics). For example, since 1900 the time for the 1 ¼ mile Kentucky Derby has varied between the record low set by Secretariat in 1973 of 1:59 2/5 seconds and a high of 2:15 1/5 in 1908 (on a muddy track). In the past 33 years since Secretariat’s record the variance has been between 1:59 and only 2:05 or less than 6 seconds. I think I would reconsider the correlation that was suggested in the article.
http://www.kentuckyderby.com/2006/derby_history/derby_statistics/
Hi, everyone.
There is a big issue for horse lovers before the Senate right now. Three foreign-owned horse slaughter plants here in the USA are killing American horses to sell to diners in Belgium, France and Japan. They kill the horses, harvest the meat, and then ship it overseas. There is a bill before the Senate right now to ban this practice in all 50 states.
Me and some friends are asking people to send an email to their senators asking them to push this bill through and vote to end horse slaughtering. The bill has already passed the US House of Representatives and this is the last hurdle before it goes to the President for his signature.
A common misperception is that the horses are old or sick – not true. Many are under 2 years old and healthy, and are sold simply for money.
Here’s how you can help – everyone needs to contact their senators and indicate they don’t want our horses dying to feed other countries.
Go to http://www.congress.org/congressorg/home/ and type in your zip code. Send an email to both of your US senators and tell them to stop this terrible practice. The vote is coming before the Senate next week so please do it NOW! :-) Thanks!!!
And here is a blog that we set up so you can read more information about it:
http://www.horsesarefriendsnotfood.com
:-) Thanks!!!
Asshe said:
“However I do remember reading that one of the males with an unusually large heart died of a heart attack. But with just one case this certainly doesn’t indicate any relation between large hearts and being at greater risk of heart disease etc.
Sorry but I can’t remember where I read this info…”
The New Zealand (yes, the Aussies did steal him, just like lamingtons, Russell Crow, and myself) horse, Phar Lap, who had an incredibly large heart (I’ve seen it), was beleived to have died of a heart attack, although now his death was believed to be caused by ingesting arsenic.
Still, maybe having a large heart is good in the short term, but just can’t keep up aftera while. Hmm…
Racehorses have really cool names. Like Eclipse and Secretariat and Citation. Those are AWESOME names.
In the racing context horses are considered old when the reach 10 – in fact most finish racing by 8 years, however hurdlers and steeple chasers peak around this age (I think..). But this is really the only equestrian sport where horses are retired at such a young age. Many great horses have won Olympic standard competitions between 12 -17 years of age – many former race horses have gone on to successful careers as eventers and the like. Barring any sever illnesses, most horses, racehorses included, live happy lives being ridden past 25 and die over 30.
Why isn’t there a corresponding movement to ban the slaughter of cows and pigs? What makes horses so special they should be exempt?
Anyway, I find it peculiar that there should not be a way to tell a horse’s heart size pre-mortem. Can’t you just X-Ray them?
Awesome article again! I have a slightly enlarged heart, passed down from my mother who in turn recieved this gentic trait from her mother. At 16 i had an abcess on the inside of my spine that ruptured and caused blood poisoning. I was told by my treating doctor that the only reason i survived was due to my larger heart. Again at 20 i was stabbed in the leg, severin g my femoral artery and once again(surprise surprise) i only survived becuase of the hearts ability to continue pumping under extreme stress ( I had lost over 50% of my blood and should have been dead) My doctor told me that, in 25 years of medicine, i was the only bona-fide miracle he had witnessed. Unfortunitly there is a price to pay for this as my mother now has a pacemaker, as it seems her heart is a little worn out and i have been told that i can expect the same. During my teenage years though i was certainly the faster, better, stronger one of my friends and family and was able to achieve moderate success in the sporting field. I’m no medical scientist but i believe there is a correlation between heart size and physical performance.
since heart sizes aren’t known until after the horse dies The heart size is not posted on a race form. However California Chrome who won the Kentucky Derby and Preakness this year has a heart that weighs 15 pounds he was beat in the Belmont by Tonalist who has a heart that weighs 17 pounds and Commissioner heart of 16 pounds. Northern Dancer Won the Kentucky Derby and Preakness he was beat in the Belmont by Quadrangle who had a heart of 16 pounds. Zenyatta has a heart of 17 pounds..Her foal will have a heart of 17 pounds Don’t know if this answers your question. I have not tried this at the track. Only learned how to do it a month or so back.
Northern Dancer had a heart weighing 15 pounds he was beat in the Belmont by Quadrangle who had a heart of 16 pounds To get another tripple crown winner you will have to have a horse with a heart of 17 pounds or bigger the 15 pound hearts will not do it. It is possible to tell the horses heart size before it is dead. There is a way to tell the heart size of horses at the track.