Horse breeders have always put their faith in bloodlines when it comes to finding a winner – now they’re putting science into their stud books
See gallery: “The not-so-natural history of horse evolution“
AND they’re off! It’s the 2.35 at the Curragh, county Kildare, on the first day of Ireland’s flat racing season. In the nick of time I manage to place a €5 bet on Whip Rule, a 2-year-old colt. His odds don’t bode well – 10/1 in a six-horse contest – but I still think I’m on to a winner. That’s not because I’ve had a hot tip from a stable boy, but because I’m confident my horse is made of the right stuff for this race.
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Genes are everything for thoroughbred racehorses. Yet although horse racing has grown into an international multibillion dollar industry, racehorse breeding still relies on the same tools as it has for the past 300 years: pedigree charts, and trial and error. Now, however, the horse industry may be placed on a more scientific footing. In the past few years there has been an explosion of interest in horse genetics, and last year a test was unveiled for a “speed gene”.
This research could help us humans too, by shedding light on people’s exercise abilities and helping to combat the effects of today’s sedentary lifestyle. Over the years, horses have been bred for exercise ability, says geneticist Emmeline Hill, who developed the speed gene test. “We can learn something from the horse as a model, in terms of the genes that are contributing to a healthy metabolism.”
Wild horses were plains animals adapted for flight. Since their domestication about 6000 years ago, animals have been selected for speed and strength, a process that has been taken to extremes with thoroughbreds. All half a million or so registered thoroughbreds in the world are descended from three Middle Eastern stallions and about 70 brood mares from Britain and Ireland in the 16th and 17th centuries.
More than three centuries of breeding have turned today’s thoroughbreds into running machines. They have huge hearts and lungs, and their muscle accounts for a phenomenal 55 per cent of their body weight, compared with 30 to 40 per cent for most mammals.
The huge sums of money tied up in racing and in other horsey pursuits such as show jumping and rodeo have led to serious investment in the study of equine genetics. In 2003 the first horse was cloned, and while clones cannot be registered as thoroughbred racehorses they can take part in other equestrian sports.
Following the sequencing of the horse genome in 2006, a few firms have started offering tests to predict racing ability based on patterns of variation among various regions of DNA. How effective these predictions are remains to be seen, but last year the horse world sat up and paid attention with the publication of Hill’s test (PLoS One, vol 5, e8645) – the first to be based on a single gene with known relevance to racing ability.
Hill’s group, based at University College Dublin, Ireland, looked at the myostatin gene, which normally acts as a brake on muscle development. In animals as diverse as mice and racing whippets, mutations have been found that stop the gene from working, endowing the animals with bulging muscles.
Myostatin appears to affect muscle mass in people too. In 2004, an extraordinarily muscular German child was found to have a mutation in both copies of his myostatin gene (The New England Journal of Medicine, vol 350, p 2682). At just 4 years old, he could hold 3-kilogram dumb-bells with his arms extended. His mother, who had just one copy of the mutated gene, was a professional sprinter.
In the blood
Hill herself is not without a pedigree, coming from a family that has bred and raced horses for generations. Her grandmother owned the Irish champion Dawn Run, a relative of the even more famous Seabiscuit, and rode as a jockey at the age of 62.
But Hill prefers studying horses to racing them. Her team focused on a point on the myostatin gene that can carry either of two bases: cytosine (C) or thymine (T). As horses, like us, have two copies of most genes, there are three possible combinations for their myostatin genes: C/C, C/T or T/T. Hill’s group tested 179 elite racehorses and found that C/C horses are speedy types that do best at short races of 8 furlongs (1.6 kilometres) or less, while T/T horses have more staying power and do best at longer races of up to 20 furlongs. C/T types come somewhere in the middle (see chart).
“Once you know the type of your horse, you can train it for what it is genetically made to do,” says Hill, who has started up a campus company, Equinome, to market the test. “A marathon runner is never going to beat Usain Bolt over 100 metres, regardless of training.”
Searching through the thoroughbred genome for other variants linked to athleticism, Hill has found that genes for insulin signalling, fat metabolism and muscle strength have been strongly selected for in recent history (PloS One, vol 4, e5767). Understanding such genes could help lead to the development of new drugs for obesity and diabetes, she suggests.
So what does the horse world make of this new approach? At horse sales, Hill hears buyers wondering if a horse is C/C or T/T, and the jockeys and lads in the training yards are talking horse genotypes. In the past, breeders used pedigrees as a proxy for genes, but Hill’s test marks a shift, says Ernest Bailey, a geneticist at the University of Kentucky who was the coordinator the horse genome sequencing project. “As breeders use the actual genes in their evaluations, they are going to be more successful in producing the horses they want.”
“At horse sales the jockeys and stable boys are talking horse genotypes”
But genes are not destiny. “We will still need to run the races to see which of the superior horses is best,” Bailey says. “The answer is not going to be in a test tube.” He also points out that there is probably no such thing as a single speed gene – there must be many genes that affect a horse’s performance. “Success is achieved in many ways,” he says. Horses “win races because of the diversity afforded by genetics, management and training”.
Maybe so, but back at the racetrack the test is all I’ve got to go on. Hill naturally keeps the results confidential, but I’ve heard that trainer Jim Bolger has been using the test in his stable. The 2.35 race is only 5 furlongs, so I’m convinced Whip Rule is C/C – a born sprinter.
The race is over in a flash. Whip Rule is one of two horses that are neck and neck as they charge the finish line. Sadly my horse is just beaten by a “short-head”. There are raucous celebrations in the stands from the winning ticket holders.
But then a steward’s inquiry is announced. Ten minutes later the leading horse is judged to have drifted in front of Whip Rule and my horse becomes the winner. Oh happy day!
From then on I make further bets on Bolger’s horses: I win some and lose more, but still end the day €30 up. Whip Rule has shown he has what it takes. After all, it’s in his genes. Probably.
