The Anatomy of a racehorses heart is one of many of Ashforth's Curiosities in his brilliant book

Posted by Lydia Unwin on


The thing about T.M.Opera O’s heart was that it was unusually big, as was the number of yen won by the heart’s owner.

Between 1998 and 2001 T.M.Opera O won 1,835 million yen, helped by 14 wins from 26 races, including 6 successes in domestic Group 1 events and one – the 2000 Japan Cup – in an international Group 1. At the time, 1,835 million yen translated into a less spectacular sounding but still satisfying US$16.2 million or about £11 million. At that time, T.M.Opera O was the world’s all-time leading prize money winner. Later, Arrogate arrived and, in 2016 and 2017, earned US$17.4 million (£13.6 million) by winning seven of his 11 races, including the 2016 Breeders’ Cup Classic and 2017 Pegasus World Cup International and Dubai World Cup.

But back to T.M.Opera O’s heart. In 2001 a team of researchers led by Kazuhiro Kamiya took a sophisticated magnifying glass to the great horse’s still beating heart and made some striking discoveries, reported two years later in ‘Heart Size and Heart Rate Variability of the Top Earning Racehorse in Japan, T.M.Opera O’ (Journal of Equine Science. Vol.14 No.3).

Kamiya and his colleagues also studied 15 other racehorses. The mean average weight of their hearts’ left ventricular mass was 3.4kg compared to T.M.Opera O’s 4.6kg (29 per cent heavier). The latter’s resting heart rate of 25 beats per minute was significantly lower than the average of 30.3 beats per minute (17.5 per cent lower).

Then there was the horses’ low frequency power and high frequency power to consider, as determined by heart rate variability. In both cases, T.M.Opera O’s was “considerably higher than those of the other racehorses.”

“These results,” the researchers concluded, “suggest that a large heart, formed by genetic factors and training, markedly enhanced the parasympathetic nervous activity and reduced the resting heart rate of T.M.Opera O.” Quite so.

The same had been suspected in 1789, when an autopsy carried out on the great Eclipse (see curiosity 20) revealed that his heart weighed 6.35kg or, as it was in those days, 14lb. Phar Lap, Australia’s equine hero during the Great Depression (see curiosity 23), had a heart of the same weight, compared to the average of 3.5kg to 4.0kg.

Then there was the mighty Secretariat, who won the US Triple Crown in 1973, establishing records for the fastest times in each of the Kentucky Derby, Preakness Stakes and Belmont Stakes, which he won by a staggering 31 lengths. One of the all-time greats, Secretariat boasted a heart estimated to weigh up to 21lb, alias 9.5kg, more than twice the average.

After carrying out an autopsy on Secretariat, Dr Thomas Swerczek said, “We were all shocked. I’ve seen and done thousands of autopsies on horses and nothing I’d ever seen compared to it. The heart of the average horse weighs about 9lb. This was almost twice the average size, and a third larger than any equine heart I’d ever seen. I think it told us why he was able to do what he did.”

During the 1970s, electrocardiographic studies led researchers to conclude that horses with large hearts were capable of greater athletic performances than those with smaller hearts. The use of ultrasound scans made it easier to evaluate heart size. Using ultrasound technology, Lesley Young, at the Animal Health Trust in Newmarket, measured the heart sizes of 400 racehorses and compared them with the horses’ official handicap ratings.

Presenting her findings in 2002, Young concluded that “A good horse nearly always has an above average heart size,” although the relationship applied to jump horses over longer distances rather than to Flat horses.

Six years later, an article by Rikke Buhl titled, ‘A Review of Structural Features of the Equine Athlete’s Heart. Is a Large Heart an Advantage for Racing Success?’ appeared in the Proceedings of the American Association of Equine Practitioners (Vol.54, 2008).

Buhl concluded that “there is a significant correlation between left ventricle size and performance of the horse measured by average prize money per start and official rating for thoroughbreds.”

A large heart enabled a horse to maximise the uptake of oxygen. Like Young, Buhl found that the benefits were seen most strongly in National Hunt horses. Other studies reached similar conclusions but also pointed out limitations to the application of these findings. There was, firstly, the problem of accessing information about particular horses’ heart size and function.

Other factors needed to be taken into account. A large heart was of little benefit if the horse’s conformation created problems, or if its training regime was suboptimal. Secretariat was admired for his physique and movement well before his exceptionally large heart was revealed. If his legs had been wonky his wonderful heart would have availed him nothing.

It’s interesting (well, you’ve got this far) but for punters seeking paradise, the search continues.


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