Just what is it that makes up a champion racehorse? Speed, certainly. Stamina, without a doubt. But, besides conformation, what factors are related to speed and stamina? Good racehorses come in all shapes, and the best built yearling at the sale doesn't always turn out a winner. Mentally, the potential champion needs a number of factors, not the least of which is courage. Willingness to run is at least as important as ability. Physically, one thing a successful horse needs is adequate lung capacity. Another is an efficient heart muscle.
Heart size radically affects the performance ability of the thoroughbred athlete, and it has recently been discovered that the gene which causes an exceptionally large heart is located on the x-chromosome. (The Australians were decades ahead of the rest of us, but it seems no one was listening.) Therefore, a colt can only inherit an oversized heart through his dam, and a stallion can only pass on the gene to his daughters. The exact heart size seems to vary from horse to horse. Multiple factors probably contribute to heart size, and the x-factor gene, being a mutation itself, probably works in conjunction with these; it "supersizes" the heart based on the existing blueprint, so to speak.
The first known case of an oversize heart was Eclipse, foaled in 1764, and he passed that gene on to many of his daughters. It is my opinion that the phenomenon known as an exceptional broodmare sire is a stallion who carries that gene. His sons can't inherit it, but his daughters can. And so can their offspring. Therefore, his daughters' sons are given the potential to significantly outperform his own sons.
The most famous such example is Secretariat. His autopsy showed beyond a shadow of a doubt that he had an oversized heart, weighing in at 22 pounds, nearly three times that of the average thoroughbred, and more than three times that of an average non-thoroughbred horse.
Secretariat's stud career wasn't unsuccessful, but while he passed on to his sons many outstanding characteristics, none of them displayed their sire's ability to sprint for a mile and a half, annihilating top notch fields and world records in the process. Essentially, Secretariat had inherited brilliant speed from his sire, the great Bold Ruler, but it was from Somethingroyal that he inherited the stamina to maintain it for classic distances. A horse tires when oxygen debt makes his muscles ache. A larger, more efficient heart enables those muscles to receive optimum oxygen for a longer period of time, provided that lung capacity is more than adequate. This therefore increases stamina. Secretariat's extreme example of a large heart probably greatly accounts for his seemingly unnatural ability to turn in performances like the 1973 Belmont Stakes.
Secretariat's second physical advantage can be demonstrated by viewing his Marlboro Cup. His stride so dwarfs that of Riva Ridge, a dual classic winner himself, that Secretariat takes one stride for every two taken by his stablemate. With these two weapons in his arsenal, Secretariat was able to become more than a champion. He was a legend.
Man o' War had the same two weapons. He was also a legend. These two were also big, powerfully built horses with excellent conformation. Conformation faults, and most horses possess many, can cause numerous problems. If a horse had an oversized heart, but failed to stay sound due to conformation defects, he might become a champion, but certainly not an infallible one. If a horse had an oversized heart, but a straight shoulder, he would fail to have a long enough stride to take full advantage of his heart capacity. And, if a horse has good conformation and the other factors necessary for speed, he could certainly become a champion without an oversized heart, and many no doubt have. He would just work harder for his wins than those who had it. He might perhaps limit his greatest triumphs to shorter distances, or, since every horse to win at a mile and a half doesn't have the luxury of an oversized heart, he would have to be rated like a mortal animal, where with the likes of Secretariat and Man o' War it was not necessary. Certainly increased stamina can be trained into a horse. Bold Forbes, a sprinter by nature, won the mile and a half Belmont Stakes due to masterful training and careful rating. Ack Ack was also better at shorter distances, but he got a mile and a quarter several times. The x-factor is not common enough to attribute all feats of speed and stamina to it, or to state that to be a success, a horse must possess it.
Increased heart size makes everything easier, naturally, but for it to serve as an advantage it must be a gift possessed by less than the majority.
It is true that a majority of thoroughbreds possess a heart that, on average, is two pounds heavier than that of other breeds. But it is when the heart size exceeds that significantly that the horse gains advantage over his rivals, and that difference is linked to the x chromosome.
Let's look at the stud career of Secretariat more closely. His greatest star was a daughter, Lady's Secret. Horse of the Year in 1986, and an impressive performer despite her lack of size, she is a definite suspect in the search for the X Factor. She wasn't unbeatable, for she didn't possess the size, powerful build, and great stride of her mighty sire. But she was sound and well made. D. Wayne Lukas called her an overachiever, and he very well may have summed it up in that one word. An X Factor horse will, given the chance, outperform its size and/or conformation. Her wire to wire sprint to win the mile and a quarter Breeders Cup Distaff is exactly the kind of performance that the oversized heart makes possible. While she has yet to pass on her ability to her offspring, time may very well tell. We'll look at her broodmare sire, Icecapade, a bit later.
Also notable was Secretariat's son General Assembly. A beautiful colt, he inherited his father's good looks, conformation, and even some of his speed. He could not, however, inherit Somethingroyal's x chromosome, and therefore he could not match the performance of his sire. He was probably the second best two year old of 1978, and at three he won the Travers Stakes and the Vosburgh Handicap. He was by no means a dud. Having failed to successfully tackle Spectacular Bid in the Kentucky Derby, however, he was criticized for failing to meet expectations arising from his sire's uncanny abilities. In 1979, no one (outside of Australia, anyhow) was aware of the sex linked nature of heart size, although the phenomenon of the broodmare sire had been well known for two centuries.
As a broodmare sire, Secretariat had much greater success, and was responsible for the remarkable mare Weekend Surprise, dam of Horse of the Year and Belmont Stakes winner A.P. Indy as well as Preakness winner Summer Squall. Secretariat's daughters also produced Storm Cat, Chief's Crown, Dehere, and more.
Now we come to the exception that proves the rule. Risen Star was by far Secretariat's best son, winning the Preakness and Belmont in 1988. His success reminds us of two facts. First of all, he may have had the x-factor; just because he couldn't inherit it from his known carrier sire doesn't mean he didn't have it, since his dam could have been a carrier. Secondly, we are reminded that heart size is not the only characteristic that makes a successful racehorse. Man o' War's entire stud career shows that clearly enough. He sired sixty four stakes winners, including the outstanding colts War Admiral, Crusader, American Flag, and War Relic, as well as the Kentucky Derby winning gelding Clyde Van Dusen. Man o' War passed on many of the qualities that made him a champion. But, he too failed to reproduce himself, because even Man o' War couldn't alter the rules of science and pass an x chromosome linked trait on to his sons.
Of course, his daughters were more consistently outstanding, and as a broodmare sire he produced 128 stakes winners and eight champions. That his son War Admiral was also a great broodmare sire was a coincidence possibly created by the fact that his dam Brushup was probably a carrier of the x factor. This would explain the Admiral's impressive performance, which despite his smaller stature outshone the deeds of Man o' War's other sons. It was Crusader who most resembled Man o' War physically; had conformation alone been responsible for performance, than Crusader surely would have reigned over War Admiral.
Brushup was a daughter of successful broodmare sire Sweep, whose daughters included Dustwhirl, the dam of Whirlaway. Two time champion and Belmont Stakes winner Sweep was out of the good mare Pink Domino, whose amazing sire Domino is a suspect. Both Domino and Whirlaway possessed a dangerous turn of speed that made people question their reality. Once again, it takes more than the x-factor to create talent on that level, but it would certainly help. Both Domino and Whirlaway died young, unfortunately, limiting the number of offspring they produced, but Domino did very well siring top colts as well as good mares, and obviously possessed a complete package of outstanding characteristics. War Admiral, if he was an x-factor horse, may have inherited the gene in another manner, but Domino is a pretty strong suspect.
War Admiral's daughter Busher was almost certainly in possession of an exceptional heart. Horse of the Year in 1945, she successfully handed defeat to older males as a three year old. Those she conquered included Armed and Stymie. She carried weight and won at a distance, setting a track record at a mile and a quarter. As a broodmare, she produced the stakes winner Jet Action, and might have had more success had she lived past the age of thirteen. She had but five foals. Her full sister Striking was an outstanding broodmare and a Hall of Fame member. To display the trait, they would need to be homozygous, of course, but Busher and Striking each had a double chance to inherit the x factor. Their dam, Baby League, an above average broodmare, was out of the great La Troienne. Dam of Bimelech and Black Helen, La Troienne was almost certainly a carrier.
We could spend all day speculating about what horses had or didn't have the magical x-factor gene. The only ones that can be proven beyond a shadow of a doubt are Secretariat, Phar Lap, and Eclipse, all of whom had their hearts weighed after death. Let's try to follow the path of the x chromosome in Secretariat back to Eclipse.
Somethingroyal, being a mare and therefore receiving two x chromosomes, could have inherited it from either parent, or both. Both were outstanding individuals, and both very well could have been carriers. Princequillo was known for his endurance, with wins including the Jockey Club Gold Cup, he led the Broodmare Sires list seven times, and was the broodmare sire of numerous high class horses and classic winners on an international scale.
Princequillo also sired several colts with notable staying ability, however, including two sons who exceeded his accomplishments, Round Table and Hill Prince, so either he was fortunate to meet up with two x-factor mares, or there was more to his talent than x-factor alone. Or, as is most likely, both of these statements are true.
Princequillo's dam was Cosquilla, a daughter of the English champion Papyrus, whose second dam was a St. Simon mare. St. Simon is definitely a suspected carrier. He had more than his share of positive qualities, and therefore by passing those on he produced several outstanding sons, Persimmon and Diamond Jubilee among them (note both were out of Hampton mares...), but his daughters had great success on the track as well as in their careers as broodmares, producing such greats as Rock Sand, an English Triple Crown winner and outstanding broodmare sire. It was from Rock Sand that Man o' War most likely received his magic chromosome.
Somethingroyal also could have inherited the x chromosome she passed to Secretariat from her dam, Imperatrice. A solid performer on the track, this fine mare produced several stakes winners. A quick glance at a five generation pedigree for Imperatrice leads me to accuse Isinglass first. An English Triple Crown winner, beaten but once, he sired the second dam of Caruso, the sire of Imperatrice.
Isinglass was by Isonomy, a possible carrier, but the gene can't be passed from father to son. Looking at Deadlock, his dam, we quickly see that her sire Wenlock was out of Mineral, a Rataplan mare. Rataplan is a good son of the great broodmare Pocahontas, and she is one of the strongest x-factor suspects in the stud book.
One thing may appear puzzling. Somethingroyal could have been homozygous for the trait, but if that were the case, why couldn't her daughter, The Bride, manage to win something more than a coin toss?
The answer is that this trait is recessive in the female, but dominant in the male, as are many sex linked characteristics. The female has two x chromosomes, while the male only has one. He will therefore express the gene, while the mare won't unless homozygous. (A good example of a recessive sex linked trait would be hemophilia). So, if Somethingroyal is homozygous for the x-factor, which is possible, shouldn't The Bride have passed on the x-factor to approximately half her offspring? In theory, yes, but luck is luck. Ask any breeder of pintos what percentage of pinto foals they manage to produce from a heterozygous pinto stallion when bred to a solid mare, or vice versa. In theory, this cross has a 50/50 chance every time. In practice, since each such cross has 50/50 odds, and the last result does not affect the next, it may take four or five such crosses to produce one pinto foal.
For a quick example of how well 50/50 chances tend to actually result in the desired outcome half of the time, flip a coin ten times. You should get heads five times. You won't. Now add to that the fact that the trait caused by the x-factor gene will only stand out in male offspring, and then only if they get the opportunity to show it. (The Bride did produce two stakes winners, At Ease and Heavenly Match.) And finally, consider the fact that The Bride was won in a coin toss where the loser got Secretariat.
Now, we have decided that in all likelihood Princequillo was an x-factor horse, and that the gene he inherited had a good shot of being passed through St. Simon. We also suspect Imperatrice of being an x-factor horse, and we've chased that gene, through a few educated guesses, to Pocahontas.
So, having accused the great St. Simon of passing the x-factor gene to both Man o' War and Secretariat, we should look at him more closely. An undefeated champion who destroyed his fields, winning the Ascot Gold Cup by twenty lengths; A great sire and a great broodmare sire. If you look at a picture of the great horse, you can't help but notice the deep slope to his shoulder, and the muscling that was evident even late in his life. He undoubtedly possessed a tremendous stride, and that was a trait he could pass on to his sons as well as his daughters.
St. Simon received his Y chromosome from his sire, the speedy but not quite immortal Galopin, winner of the Epsom Derby. His x chromosome came from his dam, St. Angela. She was by King Tom, and his dam was Pocahontas, who we already said is one of the strongest x-factor suspects in the stud book. She was the dam of Rataplan and Stockwell. Rataplan won the Doncaster Cup and 21 Queen's Plates. He was also broodmare sire to several English classic winners.
Stockwell, beaten but once in his career, was a dual classic winner and was such a great sire they called him "The Emperor of Stallions". Once again, his outstanding performance depended on more qualities than a large heart, a fact proven by both performance and the success of his sons, but it certainly didn't hurt. His daughters produced a number of outstanding horses, including Isonomy.
Now, if she indeed had it, from which parent did Pocahontas receive her x-factor? Both, quite possibly. This mare very well was homozygous for the x-factor. She was racing while in foal, in stakes company and not without success. No mere mortal mare could perform that way. Glencoe and Marpessa are each suspects, and they no doubt both contributed to her other positive qualities as well.
Glencoe won the 2,000 Guineas and the Ascot Gold Cup, and was a top broodmare sire in America. Several outstanding sons of Lexington were out of Glencoe mares, including Kentucky, Asteroid, and Norfolk.
Marpessa's tail female line reads as follows:
It is reasonable to suspect that the x-factor quietly hid for generations, then expressed itself in Pocahontas when homozygous. The other possibility is that it came through Muley, as Whiskey had the chance to inherit it from his third dam, who was by Regulus. (More about Regulus shortly) Neither Whiskey nor Muley displayed the x-factor very strongly if this was true, but it is possible.
Trampoline, the dam of Glencoe, is also a suspect, as is her dam, the remarkable Web. Prominent members of family #1, these mares' careers lead one to believe that they were almost certainly carriers.
Yet here we may be reminded that there is more to an outstanding racehorse then heart size.
Look at Web's pedigree. All of the outstanding bloodlines of her time are represented. You can literally see the ingredients of the modern thoroughbred displayed here, from their sources, so to speak. From the Godolphin Arabian and his sons Regulus, Cade, and Blank, we get powerful muscling and depth of shoulder. Cade's son Matchem was noted for his great endurance, while the Darley Arabian's sons, including the great Flying Childers and his brilliant grandson Snap, contributed speed. But it is from Eclipse that we supposedly get the mutant, sex linked gene we call the x-factor. And when we look at Web's pedigree, we see several crosses to Eclipse, yet no crosses that could have passed his x chromosome to her.
This leaves us with two possibilities; was she indeed a carrier, or were other traits responsible for her success? and if she was a carrier, then what ancestry does she share with known carrier Eclipse?
Let's explore the possibility of Regulus as an X factor horse. Eclipse, his grandson, was the first known carrier. This does not mean, necessarily, that Eclipse was the originator. The original mutation may be found in the pedigree of his dam, the successful racemare Spiletta. Looking at a five generation pedigree, instincts lead me to two suspects. Regulus, Spiletta's sire, and Cream Cheeks, second dam of Easby Snake, Spiletta's broodmare sire. Regulus was vastly superior to his rivals and a superior broodmare sire who failed to reproduce himself in his sons. He actually fits the description of an x factor stallion better than does his known x factor grandson, who was an outstanding sire, although he did not reproduce himself..
Cream Cheeks, being the second dam of Flying Childers, who was also vastly superior to his rivals, would be the second suspect. When her daughter Betty Leedes was crossed with the Darley Arabian, his speed producing characteristics and the mysterious x-factor gene may have met for the first time. The result? Whether the x-factor was involved or not the cross produced England's first great racehorse, the undefeated and legendary "Mile a Minute Childers." If the x-factor was involved, this would make Easby Snake a carrier; I see no evidence of this. Granted, he may have lacked the opportunity to display this trait, so we may never know. The Darley Arabian's male line produced plenty of speed, and Flying Childers would not have needed the x-factor to overwhelm his competition early in the eighteenth century, just speed and quality.
If Eclipse was not the original x-factor horse, but instead inherited the gene, then odds are good that Regulus was also an x-factor horse. Let's look at the stud career of Regulus. He was the broodmare sire of both Eclipse and of Rachel, the dam of Highflyer. If one were to compile a list of the ten best horses of the eighteen century, these two would undoubtedly top the list. Highflyer was undefeated in twelve starts, and he was extremely successful at stud. He sired both sons and daughters of exceptional quality, especially when put to Eclipse mares. A big horse, he possessed speed, stamina, and exceptional conformation. X-factor or not, his offspring received many gifts from him.
Sir Peter Teazle, perhaps the best of Highflyer's sons, was out of Papillon by Snap. His second dam, Miss Cleveland, was by Regulus, so Sir Peter may also have had a chance to be a carrier.
Now, if Trampoline's x-factor came not from Web, then from where? Her sire, Tramp, was good, but not superior. A Doncaster Cup winner, he sired some good horses, but he doesn't leap off the page and shout x-factor. Looking at his pedigree, we see that while full of Eclipse blood, none of the crosses fall where they need to in order to pass on an x chromosome. The case supporting an accusation of Web, and therefore probably Regulus, grows.
Web, a daughter of Epsom Derby winner Waxy, is from a long line of successful broodmares. Penelope, winner of eighteen races, was a remarkable broodmare and a strong suspect, as is Prunella, her dam, who produced the classic winners Waxy Pope and Pelisse. Prunella was by Highflyer. We have already used Highflyer's greatness to support the case for Regulus, so we know that if Regulus was a carrier, so was Highflyer.
Waxy is a tail male descendant of Eclipse, but the x chromosome can't move that way. He is out of Maria, a daughter of Herod. His second dam is Lisette by Snap. This is an outstanding pedigree, full of good genetic material, but it seems to lack a magic x chromosome. Web's x-factor had to come through Penelope.
Herod was no doubt one of the top horses of his century, but his success as a stallion is too good for him to be an x-factor suspect. He sired the winners of 1042 races. Not 142. One thousand forty two. While it was Eclipse's male line that eventually dominated, it was Herod who was the better sire at the time. And this despite the fact that Eclipse was the superior horse. I could be wrong, but I believe that Herod's success had to come from factors that could be inherited father to son, combined with the advantage of being bred to daughters of Regulus and later Eclipse. Furthermore, there are no x factor suspects in the correct places in Herod's pedigree; it contains no crosses to Eclipse (which would have been impossible since Eclipse was younger than Herod); he shares no correctly positioned common ancestors with Eclipse; and his most noteworthy ancestors are not in the position to pass down an x chromosome:
Jigg by Byerley Turk
Partner
Sister to Mixbury Galloway-Curwen Bay Barb
Tartar
Fox by Clumsey
Miliora
Milkmaid by Snail
Herod (1758)
Flying Childers by Darley Arabian
Blaze
Confederate Filly by Grey Grantham
Cypron
Bethell's Arabian
Selima
Graham's Mare by Graham's Champion
Matchem, the third linefounder from the eighteenth century, was also probably not a carrier. His dam, called Changeling's Dam or A Sister to Miss Partner, was a daughter of the champion sire Partner and Brown Farewell, a good mare by Makeless out of a Brimmer Mare. Brown Farewell was a female line descendant of the Layton Barb Mare. This makes Matchem a well bred horse of his day, especially seeing as he's by Cade, and Matchem certainly demonstrated his quality both on the racehorse and at stud, but there seems to have been no chance for him to inherit the x-factor gene.
Now, if we leave the eighteenth century and look at those horses who have truly demonstrated greatness in the twentieth century, who might be a carrier? We know that Secretariat, Man o' War, and Phar Lap were. We think that War Admiral, Busher, and Whirlaway may have been. How about Citation, Kelso, and Ruffian?
Citation was an extraordinary horse. He was by leading sire Bull Lea, but his success went beyond the speed Bull Lea was known to sire. Not only was he a Triple Crown winner who beat older horses, including a former Horse of the Year, in February of his three year old year, but after missing his four year old season, he made the most successful comeback in the history of racing, turning in multiple world record performances, and becoming history's first equine millionaire.
Hydroplane II, Citation's dam, was by Hyperion, who was a European champion and classic winner despite standing a mere fifteen hands high. Definitely a suspect. Hyperion's dam was the outstanding producer Selene. Tried and convicted.
Selene produced Sickle and Pharamond II, whom among other things were both very successful broodmare sires. She was by St. Simon's son Chaucer, and while the x-factor couldn't have traveled that path, his speed and power were passed to her sons. Her x-factor possibly came through her broodmare sire, Tristan, who was out of a Stockwell mare. Tristan won the Ascot Gold Cup, as well as three runnings each of the Hardwicke Stakes and the Champion Stakes. He was also the broodmare sire of St. Leger winner Swynford, who also won the Eclipse Stakes and two runnings of the Hardwicke Stakes.
Kelso won five Jockey Club Gold Cups. He was Horse of the Year five times. He repeatedly gave significant weight to younger horses of notable ability. And his second dam was out of a Man o' War mare. Kelso's x-factor could also have come from his broodmare sire Count Fleet, whose breathtaking performance in sweeping the 1943 Triple Crown deserves an accusation as well. And Count Fleet's third dam was a Rock Sand mare. So yes to Kelso, and probably yes to Count Fleet as well. And both have Rock Sand to thank, as does Man o' War himself.
Ruffian certainly performed like an x-factor horse. She destroyed her fields and a number of stopwatches, and displayed the ability to sprint over a distance, always leading wire to wire. To display the trait, she would need to be homozygous. Her dam Shenanigans was by the great Native Dancer, an x-factor suspect with a big stride who in turn was out of a Discovery mare. In addition to Ruffian, Shenanigans also produced Icecapade, a good stakes winner and the broodmare sire of suspected x-factor mare Lady's Secret. Shenanigans was out of Bold Irish, and therefore comes from an impressive female line and is a suspect as well.
Reviewer sired Ruffian, and while he wasn't a great horse, he was a solid stakes winner, and he had a double shot at inheriting the x-factor. His broodmare sire, Preakness winner Hasty Road, was by Discovery. His third dam was by Blue Larkspur. Both Discovery and Blue Larkspur were great horses themselves, and both were the very definition of great broodmare sires. Reviewer was also the broodmare sire of the champion mare Laugh and Be Merry.
Asked how to breed a champion, Alfred Vanderbilt responded "just breed any sire to a Discovery mare." This accurate statement resulted in, among others, Native Dancer, beaten but once, two time champion Bed o' Roses, and Bold Ruler, classic winner, champion, and Horse of the Year despite numerous injuries.
The mighty handicap champion and Horse of the Year Discovery won three Brooklyn Handicaps and carried as much as 139 to victory. Assigned 143 pounds on one occasion, it took the good horse Esposa, with a weight assignment of 100 pounds, to beat him.
Discovery was by Display, a tough horse himself, but if he possessed the x-factor gene it came through his dam Ariadne, whose second dam was by Hamburg, and whose sire was out of a Isinglass mare. Hamburg was a Horse of the Year, and his second dam was Mannie Gray, the dam of Domino. Hamburg's best offspring was the brilliant filly Artful. As a broodmare sire, Hamburg was responsible for, among others, the Kentucky Derby winning filly Regret.
Three time Horse of the Year Forego, another giant of the handicap ranks, was out of Lady Golconda by Hasty Road, who was out of a Discovery mare. And his third dam was Whirling Girl by Whirlaway.
To firm up our accusations of Whirlaway, War Admiral, and Sweep, let's look more closely at Domino's pedigree. His speed comes down from his sire, Himyar, by America's first great sprinter, Alarm. The x-factor would be passed from either Lexington, who appears repeatedly on his dam's side, or Lecompte, sire of his third dam and the son of a Glencoe mare.
Lexington, as an x-factor horse, is a strong possibility, although he is another one of those horses who had it all. An amazing performer and an outstanding sire, his male line all but died out despite the success of his sons on the racetrack, and his position as America's leading sire for a record sixteen consecutive years. As a broodmare sire, Lexington got such horses as Hindoo, Luke Blackburn, Salvator, Spendthrift, Survivor, Saunterer, Springbok, Ten Broeck, Vanguard, Montague, George Kinny, Aristides, Ben Ali, Day Star, and Grenada. This list reads like a who's who of the 1870's and 1880's.
Alice Carneal, the dam of Lexington, was the dam of several good horses. She may have inherited the x-factor from Robin Redbreast, the broodmare sire of Sumpter, who sired her dam Rowena. Robin Redbreast's dam, Wren by Woodpecker, was out of a strongly suspected carrier, Sir Peter Teazle's dam Papillon, and produced the good filly Bellissima, winner of the Oaks, the four mile Oxford Gold Cup, and two King's Plates.
One of the most difficult feats a racehorse can accomplish is to win the Triple Crown. We have already made strong cases for War Admiral, Whirlaway, Citation, and Count Fleet as x-factor horses. Secretariat is a known x-factor horse. What of other six?
The first Triple Crown winner, Sir Barton, was a champion despite the fact that he was never fully sound. Plagued by bad feet, he nonetheless swept the 1919 Triple Crown and was the best older horse of 1920. His dam, Lady Sterling, was by Belmont Stakes winner and Horse of the Year Hanover, who is out of Bourbon Belle by Bonnie Scotland. Bonnie Scotland's third dam is by Whalebone, a son of Penelope, and his fifth dam is by Sir Peter Teazle. Sir Barton's most notable offspring was the filly Easter Stockings, and failing to sire anything else of note, he ended up in Wyoming.
Gallant Fox was a big, well made horse, and he proved himself exceptional by winning not only the Triple Crown, but also the Dwyer Stakes and the Lawrence Realization. He had two very successful brothers as well; his full brother Fighting Fox and his half brother Petee-Wrack, who won the Suburban Handicap. This definitely is cause to accuse Marguerite, their dam. She contributed the x-factor that allowed Gallant Fox to take maximum advantage of the speed and power he inherited from Sir Gallahad III. Marguerite was by Celt, a good son of Commando. Celt was out of an Amphion mare, and Amphion's second dam was by Rataplan. Incidentally, Sir Barton's good daughter Easter Stockings was out of a Celt mare.
As for Gallant Fox's son Omaha, he is out of Flambino by Wrack. Wrack, broodmare sire of Hildene, is out of an Isinglass mare. Hildene is an extremely strong x-factor suspect, being the dam of Horse of the Year Hill Prince, the champion colt First Landing, and Satsuma, the dam of the outstanding Cicada.
If any horse outperformed his conformation, it was the club footed comet Assault. His sire Bold Venture won the Kentucky Derby, but Assault's dam Igual had two chances to inherit the x-factor, and therefore probably passed it to her son. Igual's sire was the great Equipose. Her second dam was Man o' War's full sister Masda.
Equipose was twice Horse of the Year. Plagued throughout his career by a chronic quarter crack, he missed the classics as a three year old, but was a champion at two, four, five, and six years of age. He carried weight, and won at a distance. His broodmare sire Broomstick set a track record winning the 1903 Brighton Handicap, and earned a membership in the Hall of Fame. His second dam was by Epsom Derby winner Bend Or, whose daughter Fairy Gold produced Fair Play and Friar Rock.
If Bend Or was a carrier, it might be somewhat difficult to find the source. Much speculation surrounds his dam's identity. Some claim he was actually out of a mare named Sandiway, and that the mares had switched foals. A conflicting story claims that it was Rouge Rose who was switched as a foal, and that she isn't actually out of Ellen Horne. Regardless, Bend Or's accepted pedigree has him as a son of Rouge Rose, and assuming that is correct, the source of his x chromosome was possibly Highflyer. Rouge Rose's dam Ellen Horne is by Redshank, whose broodmare sire Selim is out of an Alexander Mare, who is in turn out of a Highflyer Mare.
This speculative path accuses Redshank and Selim of being x-factor horses. This doesn't ring true. Rouge Rose's sire Thormanby is a more likely suspect. Winner of the Ascot Gold Cup and the Epsom Derby, he was out of the durable and very successful Alice Hawthorn, whose fifty two wins included two Doncaster Cups, a Goodwood Cup, and the Ascot Gold Vase. She was by Muley Moloch out of Rebecca by Lottery. Doncaster Cup winner Lottery is a suspect, being out of Mandane, dam of several very successful horses.
But back to our Triple Crown winners. Seattle Slew certainly turned in the type of performances typical of an x-factor horse who had everything else a champion thoroughbred needed as well. His Kentucky Derby was impressive. Slew won despite the obvious nervousness he displayed in the paddock as well as a bad start. As a sire, he proved he had qualities other than the x-factor, siring champions like Slew o' Gold, Swale, and A.P. Indy. Granted, Slew o' Gold and A.P. Indy were out of almost definite x-factor mares, Alluvial by Buckpasser and Weekend Surprise by Secretariat, and Swale's third dam was by Nasrullah. Seattle Slew's x chromosome may have come from his third dam, Myrtle Charm by Alsab. We'll get to him in a bit.
My Charmer, the dam of Seattle Slew, had produced nothing notable prior to Seattle Slew, but once being put to better stallions, she produced Lomond, winner of the 2,000 Guineas, and Seattle Dancer. Bold Reasoning sired no other horses of significance.
Was Affirmed an x-factor horse? Affirmed's broodmare sire Crafty Admiral was out of a War Admiral mare and his third dam was by Mahmoud, so he had the opportunity. He had outstanding conformation, so with the x-factor he would have been a superb performer. He won the most hotly contested Triple Crown in history, and was Horse of the Year as a four year old as well, so his performance qualifies. While not unsuccessful as a sire, he has yet to reproduce himself, with his daughters outshining his sons.
Now how about a few of those horses that became champions despite "modest" pedigrees. Three famous examples from the thirties and forties spring to mind. Stymie, Alsab, and Seabiscuit. The success of Stymie, former claimer turned leading money winner, was explained by writer C.W. Anderson. "Both his sire and his dam were out of Man o' War mares." And from his second dam Stymie may have inherited the x-factor, and the increased heart size he gained from that gene would have helped him accomplish those breathtaking stretch drives that made him so famous.
Seabiscuit, who was so lame he could barely walk, still managed a career in which he defeated War Admiral, earned Horse of the Year honors, and won the Santa Anita Handicap, at the time the world's richest race, at the age of seven. His broodmare sire was Whisk Broom II, who by sweeping the 1913 Metropolitan, Brooklyn, and Suburban Handicaps became the first winner of the Handicap Triple Crown. Whisk Broom II's second dam was by the great Hindoo, who was out of a Lexington mare.
Alsab's dam may once have sold for ninety dollars, but she probably carried the x-factor. Her dam was a Fair Play mare. Her second dam was by St. Simon. Alsab, a seven hundred dollar yearling purchase, won the Preakness and the Belmont, and later defeated Whirlaway in a match race.
A more recent Cinderella horse is the great gelding John Henry. No one had ever heard of his sire, Ole Bob Bowers, and he had numerous conformation problems. He was cranky. He was gelded in an attempt to make him grow. But he was Horse of the Year twice and at one time he was the world's leading earner. And all that without even starting in a big three year old race. John Henry's dam? Once Double was by Double Jay, a successful son of the Whisk Broom II mare Broomshot. John Henry's third dam was by Mahmoud, whose dam Mah Mahal was by English Triple Crown winner Gainsborough out of a mare by The Tetrarch, that undefeated legend who was often described as a freak of nature.
Double Jay may not have been a carrier, although he had the chance to be, but Once Double certainly proved to be. Her dam had a double chance to inherit the x-factor, and her son's performance proved exceptional.
The Tetrarch sired Europe's flying filly, the brilliant Mumtaz Mahal, whose daughters included Mah Mahal, the dam of Mahmoud, Rustom Mahal, the dam of Abernant, and Mumtaz Begum, who produced the speedy but temperamental Nasrullah.
Vahren, the dam of The Tetrarch, was by the classic winner Bona Vista, whose dam was out of a King Tom mare, but it was just as likely that The Tetrarch came by his x-factor through the female line. His sixth dam was by Rataplan.
As for Gainsborough, his pedigree is full of x-factor suspects, but the only one in the right place to be guilty in his case is Epsom Derby winner Bend Or, sire of his third dam.
La Troienne was the matriarch of Idle Hour Stock Farm. A superior mare in every way, she produced quality whether she passed on the x-factor or not. She produced two champions who became Hall of Fame members, Bimelech and Black Helen. Her daughter by Bubbling Over, Baby League, was the dam of Busher, Mr. Busher, and Striking. Big Hurry was the dam of Searching, Bridal Flower, The Admiral, and Saratoga Cup winner Great Captain. Businesslike, one of several good daughters by Blue Larkspur, produced Busanda, who won the Alabama Stakes, the Suburban Handicap, and two runnings of the Saratoga Cup. Even more notably, Busanda was the dam of the great Buckpasser. La Troienne also produced Big Event, Bee Ann Mac, Belle Histoire, Belle of Troy, and Besieged.
Searching produced the outstanding daughters Affectionately and Priceless Gem. Affectionately was a champion herself, and produced Horse of the Year Personality. Priceless Gem was also successful on the track, winning the 1965 Futurity, but was better known for producing Allez France, the brilliant winner of the 1974 Prix de l'Arc de Triomphe.
Affectionately was very possibly a homozygous x-factor horse, being by Swaps. His second dam was by War Admiral, so Swaps had the opportunity to inherit the x-factor, and he overcame many difficulties to not only win the 1955 Kentucky Derby, but also to become the 1956 Horse of the Year. After racing with a quarter crack, Swaps was out of action for six months following his match with Nashua, and when he did return to the track, Swaps still wasn't sound. Racing on three legs, the brave horse carried as much as 130 pounds to victory in eight races, setting four world records and equaling another before his life was threatened by a severely broken hind leg.
Swaps' rival Nashua himself may have been an x-factor horse. He was an exceptionally talented horse, but along with his sire's brilliant speed, he also inherited his tendancy to sulk. Nasrullah, a champion at two, was unsuccessful in the classics not due to lack of ability, but rather due to his refusal to run when asked. Nashua was better, but his riders rarely knew whether or not the horse would run his race. Nashua's broodmare sire Johnstown was out of La France by Sir Gallahad III. Sir Gallahad's second dam was Concertina by St. Simon. In the conformation department, Johnstown was something less than perfect, but he proved his ability to run nevertheless, winning the Kentucky Derby and Belmont Stakes. At stud, he managed to sire a mere six stakes winners, yet was a leading broodmare sire. His broodmare sire Sir Gallahad III, both an outstanding sire and an outstanding broodmare sire, was America's leading broodmare sire from 1943 through 1952.
The fabulous mare Dahlia, who handed defeat to top class colts on both sides of the Atlantic before producing four grade I winners as a broodmare, was by 1968 Prix de l'Arc de Triomphe winner and "Horse of the World" Vaguely Noble, and her third dam was by Gallant Fox.
So, this could go on for a week, but what good is all of this speculation about the x-factor? If nothing else, it is a delightful way to pass the time, and a good excuse to reminisce about the deeds of champion thoroughbreds throughout history.
Make your own accusations. See if you can make them stick. Who knows, perhaps your musing, when applied to a yearling sale catalog, will land the next Seattle Slew in your barn.
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