The death of the champion thoroughbred Secretariat in October 1989 and his subsequent autopsy findings revealing an enormous 22lbs heart size was the inspiration behind writer Marianna Haun and her 1997 work the X-Factor Theory claiming that the large heart gene is located on the X-chromosome hence meaning that a colt foal can only inherit an over-sized heart from his dam and as a stallion this can only be passed on through his daughters.
Such a brave theory is only that and in more recent times with modern day mapping of the equine genome there is no scientific confirmation that heart size is passed on via the X chromosome.
But what we do know from in the thoroughbred world is that certain female lines can throw horses that carry larger hearts than normal and this size can vary dependent on the taproot source.
Marianna Haun in her famous workings of the late 1990's contended that 28%of the thoroughbred population carried the large heart gene in some shape or form.
Large hearts of up to three times normal size ( estimated at 6 lbs back then ) were initially attributed to the male forebear Eclipse ( 1764 ) who possessed a 14 lbs heart ( the same size as that of Phar Lap's ).
A decade or so later along came Diomed ( 1777 ), the best racehorse in Great Britain since Eclipse, whose daughters it was claimed could pass on 18 lbs hearts.
A widely speculated belief was that the mare Pocahontas ( 1837 ) was the source of all present day large hearts, something widely dispelled by large heart authority Harold Matthews who claimed that Pocahontas possessed a 15 lbs heart and because of this she was only capable of passing on a 15 lbs heart, in other words the heart size does not go up or down but rather remains constant from generation to generation.
Matthew's identified four what he termed " base root " large heart mares originating from in the mid-1600's.
These included Darcy's Royal Mare ( 1690's ), the source of an 18 lbs heart, Royal Mare ( circa 1665 ) and Montagu Mare ( circa 1650 ), both the source of 16 lbs hearts, and the Vinter Mare who writer James Hardiman in his work "Confused Pedigrees and Mistaken Identities" believes was the same mare as the Montagu Mare by another name.
It has been claimed that early large heart progenitors were in existence before the thoroughbred was established, many of unclaimed parentage originating at Darcy's Stud, being left over "Hobby-Running" horses of King Charles reign ( aka Royal Mares ) of which there was an estimated population of just over 100 mares.
These mares did not carry any Barb, Arabian or Turk appendages of the "Oriental" breeds, the first of these entering the thoroughbred breeding genepool being the Old Moroccan Barb ( aka Fairfax Moroccan Barb ) in 1637 as seen in the pedigree of the Spanker Mare.
So can we relate any of this development of the large heart gene inheritance in the thoroughbred across to the standardbred, a breed which is far younger in establishment but which derived much of it's origins from the thoroughbred breed in association with other breeds of defined gait such as the Clay and Morgan breed?
In an attempt to answer this question we would like to focus back on the thoroughbred stallion Diomed.
Eclipse has long been considered as a prime mover in the development of the large heart gene in modern day thoroughbred pedigrees through his daughters but it is perhaps his near contemporary Diomed that has had a far more profound effect on the modern day standardbred.
Diomed was intensely linebred to the Spanker Mare ( no fewer than 9 close-up presences including this mare being his own 7th dam ) but more importantly he carries the large heart gene of Darcy's Royal Mare ( a source of 18 lbs hearts ) being out of a mare named Sister To Juno, by Spectator, out of Partner Mare, out of Bonny Lass, by Bay Bolton, out of Makeless Mare, out of Brimmer Mare, by Brimmer, out of Darcy's Royal Mare.
Whilst other large heart sources are attributable in the standardbred world as coming through the little known origins of the stallion Pilot Jnr ( and passed on through his daughters ) other acclaimed female sources are the likes of Midnight ( 1865 ) a daughter of Pilot Jnr with two lines of Diomed and a line of Glencoe ( another thoroughbred large heart source ), Esther ( 1860's ) from the Diomed sireline and possessing five lines of Diomed along with her dam being bred on a 3x3 reverse-sex cross to Glencoe, and Miss Russell, the last-mentioned being a daughter of Pilot Jnr out of Sally Russell, the latter also from the Diomed sireline.
In contemporary standardbred breeding circles any mention of the large heart gene and first thoughts move towards Tar Heel or more specifically towards the daughters of Tar Heel.
This is little surprising as Tar Heel's tenth dam is the thoroughbred Robert Wickliffe Mare, a daughter of Diomed.
This means that Robert Wickliffe Mare was a carrier of Diomed's large heart gene directly attributable to Darcy's Royal Mare ( a source of 18 lbs hearts ).
Of particular interest here is that Robert Wickliffe Mare is also the granddam of Family 558 matriarch Jessie Pepper which sees the maternal line through Princess Royal, Roya McKinney, Rose Scott, Rosette and Leta Long all equipped with the large heart gene.
From yesteryear we have the stallions Kentucky and No Nukes as well as present day stallions such as Rock N Roll Heaven descending from the Jessie Pepper family.
Daughters of these male influences are potential large heart gene carriers.
But for now, let us return to Tar Heel and more specifically his own pedigree composition.
Tar Heel is by Billy Direct out of Leta Long, by Volomite out of Rosette.
Whilst his sire Billy Direct does carry the presence of Midnight deep in his maternal bloodlines it is through his dam Leta Long that Tar Heel's large heart gene is derived.
But from which side of her pedigree is the key question?
Leta Long's sire Volomite is out of the mare Cita Frisco who is by San Francisco out of Mendocita.
Mendocita is a daughter of Esther ( see comments earlier as above ).
San Francisco's dam is Oniska who is linebred 4x5 to Miss Russell ( also see earlier comments above ), a daughter of Pilot Jnr.
Miss Russell is herself heavily inbred to strains of Diomed inheriting one strain through the dam of her sire Pilot Jnr with her own dam Sally Russell being more intensely bred to Diomed than any other female Stud Book product.
Plenty of genetic connections to large heart influences here but it is through Leta Long's dam Rosette that the large heart gene has been passed to Tar Heel according to "the experts" on this subject.
It is not our intention to be contentious here but rather just informative.
Rosette is claimed to have derived the large heart gene from her sire Mr McElwyn ( even though her damline traces directly back to Diomed ) who in turn derived his from his dam Widow Maggie who got hers from Peter The Great who got his from the brilliantly fast mare Santos.
Santos got her gene in turn from her sire Grand Sentinel who got his from dam Maid Of Lexington who got hers from Mambrino Pilot who inherited his from Juliet, another daughter of Pilot Jnr.
And from Tar Heel down the line the large heart gene passes with Bret Hanover inheriting the large heart gene from his dam Brenda Hanover, a daughter of Tar Heel, meaning Bret Hanover had the ability to pass on the gene through his daughters as well.
Before we leave our segment on Tar Heel we would like to share a couple of interesting facts on this stallion.
Tar Heel derived his name from the state of North Carolina where the practice of stripping pine trees to produce turpentine earned these workers the nickname of "Tar Heelers".
Tar Heel, a Little Brown Jug winner himself, was known as the "King Of Queens" in the breeding barn because the genes he passed onto his daughters were considered "very special".
Even today, we still laud the deeds of a Tar Heel daughter such as Romola Hanover when we peruse the pedigrees of current top stallions such as Art Major and Captaintreacherous.
Back in the 60's, 70's and early 80's it was claimed that Tar Heel's daughters propped up most stallions and both launched and saved many as they invariably produced a stallion's best runner.
Tar Heel ( 1948-82 ) lived to the tender age of 34 years at a time when the average lifespan of standardbred horses was 24 to 27 years. A son of Tar Heel in Waco Hanover recently became the longest lived standardbred on record reaching 41 years and 281 days.
One can only ponder at the thought that some of these achievements were heart related.
The interest in large inherent hearts and heart scores will always remain when one can find or develop a superior "V8 versus a 4-Cylinder" product.
A larger heart can pump more oxygen giving the horse optimum speed, greater endurance and capacity for exercise.
Australian researcher Dr James Steel created the Heart Score as a genetic marker for X-Factor through the use of an Electrocardiogram ( ECG ) to measure heart size, a scale that correlates heart weight, stroke volume, cardiac output and aerobic power.
Heart scores of average horses were typically in the range of 104-116 but Steel determined a break point of 117 for female and 120 for male horses to pinpoint potential larger heart animals.
As a point of interest here Secretariat was asserted to possess a heart score of 180.
Another study of standardbred ( trotters ) by Nielsen and Vibe-Petersen of the Royal Veterinary and Agricultural University of Copenhagen found that 41 stallions with a heart score of 115 or greater amassed double the earnings of 81 stallions with heart scores below 115.
In conclusion, on this non-exact science of the large heart gene, we do hope though that your funds investment scheme does include a few shares in a medical instruments manufacturer as the demand for stethoscopes begins to reach insatiable heights in the quest for that larger hearted horse with the competitive edge.
Premier Pedigrees was born out of Ken Mackay's passion for horse pedigrees to offer a very affordable pedigree matching service and valuable recommendations to new and existing Australian and New Zealand clients for both thoroughbred and standardbred mares.