[AusRace] From The Economist

[L.B.Loveday]

A NEW STUDY ASKS WHETHER RACEHORSES HAVE HIT THEIR GENETIC PEAK

BUT THE BREEDERS TRYING TO IMPROVE THEM MAY BE MISSING A TRICK

 Jun 7th 2023

	For decades there was an apparent paradox in horse-racing. The sport
is lucrative (Mage, the winner of this year’s Kentucky Derby, earned
his owner $1.9m) and simple—the fastest horse wins. Horses with good
results and a good pedigree are used as breeding stock for the next
generation. Horse-breeders were armed with plenty of data, a single
trait to optimise, and strong incentives to do so. Yet several studies
suggested that, despite their efforts, race times were not
improving.Listen to this story.Enjoy more audio and podcasts on iOS
[1] or Android [2].

	The most common explanation was that, physiologically speaking, it
was increasingly difficult to breed a horse that ran faster than
existing horses already do. The modern thoroughbred racing horse dates
back at least three centuries. Perhaps the years of selective breeding
had already discovered and exploited almost all of the breed’s
genetic potential. 

	That did not make sense to Patrick Sharman, a racing enthusiast and
geneticist at the University of Exeter, in England. After all, cattle
breeding has been going on for hundreds of years, yet continues to
create cows that produce more milk. Artificial selection applied to
chickens is still raising plumper birds. It would be odd, he thought,
if racehorses were the one domesticated animal that humans could no
longer improve. So, along with Alastair Wilson, who had once been his
PhD supervisor, he started digging.

	Their first paper was published in 2015, and examined a dataset of
British races going back to the 1800s, much larger than in other
papers. It found that, contrary to accepted wisdom, horses have indeed
been getting faster. In sprint races—those run over five to seven
furlongs (1-1.4km)—the average speed needed to win has increased by
about 0.1% each year since 1997. Their latest paper, published on May
27th in _Heredity_, tries to assess how much of that improvement is
attributable to genetics. In other words, is the time-, energy-, and
money-intensive profession of horse breeding worth the faff? 

	The answer appears to be yes—though less so than breeders might
like. By linking a large performance database, containing nearly
700,000 race times recorded in Britain between 1995 and 2014, to a
family tree of more than 76,000 horses, they found that speed is
heritable, albeit weakly, and that breeding is improving it, but
slowly. 

	The boost is most pronounced for sprints and middle-distance races
(8–12 furlongs). Drs Sharman and Wilson conclude that around 12% of
the variation in the speed of horses at these distances comes down to
genetics. (This is about the same heritability as neuroticism or
lifespan is in humans.) And they found that improvements to those
genetics accounted for more than half of the increase in speed seen
over that time period. The rest, says Dr Sharman, is probably down to
hard to measure, non-genetic factors such as better nutrition and
veterinary care or improved jockeying technique.

	When it comes to longer-distance races, it is not clear that times
are improving. One reason, says Dr Sharman, may be that the genes that
are good for sprinting do not necessarily make for good endurance
athletes. Breeders seem to be selecting for sprint performance because
it offers quicker commercial returns. Sprinters tend to start running
at around two years old, long-distance horses at three.

	Horse-breeders may face other trade-offs, too. Selecting solely for
speed may increase the risk of injury. (Churchill Downs racecourse,
where the Kentucky Derby is run, suspended racing for a month from
June 7th, after more than a dozen horses had died following injuries
over the past six weeks.) Temperament matters, too—a fast horse is
of little use if it is unrideable. 

	Despite the difficulties, there is also evidence that breeders might
be leaving some horsepower in the genetic tank. At least in Britain,
says Dr Sharman, breeders still rely, to some degree, on their
professional judgment when assessing horses. Less intuitive, more
objective statistical techniques have transformed other sports, most
famously baseball, over the past couple of decades. Horse-racing too
may be ripe for its “Moneyball” moment.■

	 


Links:
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[1] https://economist-app.onelink.me/d2eC/bed1b25
[2] https://economist-app.onelinkme/d2eC/7f3c199

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