There are probably as many factors in the making of a good horse as there are ways a horse can find to lose a race. Whether picking a horse in the sale ring or the form guide, the task is formidable.
Old-timers will quote breeding, conformation and temperament as the keys to selecting a yearling. But what about the contributions of feeding, training, soundness and good old Lady Luck? They all play a part before that shiny colt or filly in the sale ring greets the judge a winner.
While many horses are chosen only after a detailed study of their pedigree, followed by a long and eagle-eyed examination of conformation, many more are chosen on the spur of the moment because the horse moved well in the sale ring or it fitted a budget or even because its colour or markings caught the eye of the partner of the buyer.
Breeding, conformation temperament and even movement, are all valid criteria, one way or the other, but unfortunately they have one basic flaw. It’s not really possible to say by how much you increases the chances of finding a winner or how much the horse might win in prizemoney, by selecting a horse based on any of the above. I’ve no doubt they do, but by how much?
But what if there was a method of selecting a horse that is likely to win twice as much prizemoney as the one in the stall next to it. Some researchers believe they have discovered just that and I, for one, tend to agree with the theory, although I hasten to add that it is just that, a theory.
It’s called the Large Heart Gene Theory (LHGT) and the seeds of it are as Aussie as Phar Lap, whose heart incidentally weighed in at 14 pounds, about double the average of the day.
In 1977 Australian vets Dr. J. D. Steel and Dr. A. Stewart published the results of a study that found that whilst there was no significant correlation between the heart size, as measured in a heartscore* test devised by the doctors, of a sire and his progeny there was a significant correlation between the heart size of a mare and her progeny. There appeared to be a sex-link in the inheritance of a larger than average heart.
*Dr. Steel had been studying the sizes of horses’ hearts since the 50s and developed the heartscore scale based on electrocardiogram (ECG) measurements of heart size, stroke volume and cardiac output.
|
Heartscore (msec) |
Heart Weight (Kg) 1kg=2.2lb |
Stroke Volume (L) |
Cardiac Output (L/min at max output) |
|
100 |
3.0 |
0.5 |
100 |
|
110 |
3.8 |
0.75 |
150 |
|
120 |
4.6 |
1.0 |
200 |
|
130 |
5.4 |
1.25 |
250 |
Heartscore has been linked to increased performance by a number of researchers.
· Dr. Stewart determined that heart size makes up 23% of a racehorse’s quality.
· Danish researchers working with trotters found that stallions with a heartscores above 115 earned over twice as much as stallions with heartscores below 115.
· British researchers found a significant correlation between Timeform rating and heartscores for three-year-olds but not for two-year-olds, presumably because in the latter the heart is not fully grown
However the theory of the presence of a gene for a large heart was not widely known until US researcher Marianna Haun interviewed Dr. Gus Cothran of the University of Kentucky. Dr. Cothran suggested the gene for a large heart might be a sex-linked recessive gene, which arose from a mutation of the normal gene and would be traceable to a single source.
In her book The X Factor: What It Is & How to Find It- The Relationship Between Inherited Heart Size and Racing Performance, Marianna Haun traces the LHG in American thoroughbreds to one single mare, Pocahontas (GB) who was foaled in 1837. Pocahontas in turn traces to Eclipse (GB) b.1764, believed to be the font of the large heart gene.
[Does Phar Lap trace to Pocahontas? Yes, he does- there are at least five lines. But if the theory is correct, only the line through his dam-sire Winkie and his dam Conjure is the source of his large heart.]
On his death in 1989, that great US racehorse Secretariat was discovered to possess a 22lb heart, well over twice the average at that time. This inspired Haun in the search for the source of this large heart and suggested to her the possibility of a gene that allowed its inheritance.
Anyone who has seen the video of Secretariat’s Belmont Stakes win, arguably the greatest racehorse performance of all time, would agree that only a horse with a large heart could do what he did that day. The oxygen demand needed to sustain such a prolonged run at World record-breaking speed could only be supplied by a well above average heart.
Haun identified four stallions that appear to be the conduits of the large heart gene to modern thoroughbreds. They are Princequillo, War Admiral, Blue Larkspur and Mahmoud. All are descendants of Eclipse.
Of the four, the Princequillo line appears to result in larger hearts than the others.
But all this is not necessarily brand new. The basic concept of the LHGT, that the gene is passed on the female chromosome, fits well with some tried and true principles that horse breeders have used for a very long time. Breeders have long known the importance of the tail-female line, the broodmare sire and the sire’s dam in a horse’s pedigree. Since the gene is passed on the female (X) chromosome, it would seem that almost intuitively, horsemen have known the basis of the idea all along.
So what does this mean to the breeder or buyer of a horse?
You don’t always have to have a detailed understanding of genetics and have a memory bank of known large-hearted horses on tap to spot a likely large-hearted horse.
· Mares that produce a large percentage of winners are very likely to be large heart gene carriers, in which case there is a 50% chance her sons will be large-hearted.
· Mares that produce all winners stand a good chance of being Double Copy mares. This means they are homozygous for the large heart gene ie both their heart size genes on each of their X chromosomes are the LHG. All their foals will get the LHG and the colts will be 100% large-hearted. Fillies will only be large-hearted if they get another LHG from the stallion.
· A horse that has won a race of 1600m or longer in fast time is also a prime candidate to be large hearted. If it’s a stallion then all its filly foals will inherit the LHG but will need a second from the dam to be large-hearted. Its colts will not get its large heart gene as they only inherit a Y chromosome from their sire. They must get one from the mare. Champion staying mares are rarer and are probably the sought after Double Copy mares that often form the basis of successful studs, whether the stud owners know it or not.
· Broodmare sires with a good strike rate (>40% winners to runners) are obviously passing on something and if many of the wins are in longer races, then it’s probably a large heart that is responsible.
· The presence of small curly ears may be an indicator of the LHG. Several researchers have noted that small, curly ears appear to be associated with large-hearted horses. Perhaps the gene for this characteristic is also on the X chromosome and is a fellow traveller with the LHG in much the same way the author inherited red hair, freckles and blue eyes as a package.
Again the best way to illustrate how the LHG is passed on is by using an example.
Eavesdropper is a stallion currently standing at Emirates Park. Through him Australian breeders have the opportunity to acquire the LHG that propelled Secretariat to that amazing Belmont Stakes victory; the Princequillo heart.
Let’s take a look at his pedigree, one that is littered with large hearted horses and in particular, numerous much coveted, Double Copy mares.
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EAVESDROPPER |
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Double Copy mares |
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single copy |
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foundation large heart sire |
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According to the theory, Eavesdropper is guaranteed to be large-hearted since his dam Weekend Surprise is a known Double Copy mare. Herself a winner of seven races- including incidentally the Pocahontas Stakes- and over $400,000, she previously produced champion sires A.P. Indy & Summer Squall and was 1992 US Broodmare of the Year. Dosage enthusiasts will note her phenomenal figures of DP = 12-19-25-4-0 (60). And to top it off she is a daughter of the mighty Secretariat, making her one of a very select group. As broodmares go they don’t get much better.
Note that Eavesdropper’s LHG did not come from the large-hearted Kingmambo, since colts do not get their X chromosome from their sire. That’s not to say though that the presence of a large-hearted sire doesn’t in some way attenuate the effect in the case of a colt. It presumably is always a plus that a parent is large-hearted.
Eavesdropper’s record of 16 starts, 3 wins for $167,794 plus a third in a Group 3 is not in the league of his half-brothers but already he is producing good winners. Tio date worldwide he has sired the winners of 96 races from 152 runners (63%). Significantly there appears to be the sex bias we would expect of a LHG sire. His fillies are averaging 69% winners/runners while his colts and geldings are lagging on a still very credible 57%.
In conformation he is remarkably similar to his grandsire Secretariat and of particular note are his small, curly ears.
In time, if the Large Heart Gene Theory is proven to be accurate, I would like to see stallions and mares names being annotated with a LHG+ or LHG++ as an aid to breeders. Eg Eavesdropper (USA) LHG+ and Weekend Surprise (USA) LHG++
For now, it’s just a theory but one with considerable evidence in its favour and one which horse breeders, buyers and punters alike might like to add to their arsenal in their quest in picking a winner.
Geoff Richardson – GG Racing Tours
About the Author
Geoff is a Science graduate and former Industrial Chemist and High School Science teacher.
He is now a Sydney businessman who also finds time each year to escort a group of racing/horse enthusiasts to France, England and Ireland.
There is absolutely no scientific proof at this time that the large heart gene theory has any merit.
It is just that at the moment- a theory.
Hi Rhonda – I totally agree. Since I published Geoff Richardson’s article in 2013 and there there has been significant progress in equine gene mapping, it looks like this theory could be baseless, and that even if a racehorse has a ‘large heart’, that it doubtful that is will cause it to run any faster. Anne Peters has written an excellent piece on the subject – http://www.pedigreegoddess.com/PedigreeTheory/X%20Factor.htm
You said in the article that the origins of the large heart theory areas Australian as Phar lap. Phar lap was a kiwi bro 🤙🏾
Hi Hugo
I write 90% of the articles on my website, but I didn’t write that particular article (author details at the bottom) so unfortunately I can’t correct that error!
Thanks for reading.
Jane
Unfortunately eavesdropper was taken from Al shaab stud by armed militia in lybia fate of the horse is unknown 😢
That’s very distressing, Don. Let’s hope they value blueblood horses.