Galloping ahead (Image: Scott Barbour/Getty)
Racehorses have been getting ever faster in races over all distances, a study of finishing times over the past 162 years has found.
The findings challenge previous research that thoroughbreds had reached the limits of their speed. If anything, the improvement among sprinters is now accelerating.
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鈥淥ver the past 15 years, sprinters have improved faster than over the previous 150 years,鈥� says of the University of Exeter.
Sharman and Alastair Wilson, also at Exeter, analysed 616,084 race times in the UK by 70,388 horses between 1850 and 2012. They then took a closer look at races between 1997 and 2012, for which more extensive and accurate data was available, including the speeds of non-winners inferred from finishing times.
The results show that since 1850, the speeds of winning horses in elite races have improved by 9-13 per cent, depending on the distance run. Winning horses now run between 1.5 and 2 metres per second faster than their counterparts did in 1850.
In the period between 1997 and 2012, sprinters improved most, adding 0.1 per cent to their speeds per year. Non-winners improved, too, adding between 0.03 and 0.09 per cent to their speeds per year.
So a 2012 horse would beat a 1997 horse in a sprint race by around 17 metres. The average winning margin in elite races is just 3 metres.
Speed gene
鈥淭he big question is why the improvement?鈥� says Sharman. 鈥淚s it that we鈥檙e breeding more successfully or the environment 鈥� factors such as better nutrition, changes in veterinary practice or training methods?鈥� he asks.
, from Trinity College Dublin, says that teasing apart genetic and environmental influences will be tricky.
鈥淚t鈥檚 notoriously difficult to disentangle genetic from management factors in horse racing,鈥� he says. 鈥淚nevitably, they are confounded, as better bred horses go to better trainers, for example.鈥�
He thinks much of the improvement is down to selection.
鈥淭hese analyses support the notion that selection is shifting speed, and more so at shorter distances,鈥� says Cunningham. 鈥淪election is becoming more effective, with extended use of top stallions and increasing use of selection for a 鈥榮peed gene鈥� 鈥� a variant of the gene that makes myostatin, a muscle protein.鈥�
Sharman believes that sprinters have improved fastest because breeders in the UK have focused more on winning short-distance races. 鈥淭hey do tend to select for speed rather than long-distance stamina,鈥� he says.
So can the horses carry on getting faster?
鈥淭here鈥檚 got to be a limit at some point, but we don鈥檛 know where that limit is,鈥� says Sharman. 鈥淎t some point, there will be physiological and mechanical constraints that will prevent further improvements. Maybe they鈥檝e already been reached for middle- and long-distance runners.鈥�
Not everyone was impressed with the gains in speed, however.
鈥淭he annual rates of improvement are very small, despite the attentions not only of breeders and genetic improvement but also of vets, nutritionists and other animal scientists,鈥� says of the University of Edinburgh. 鈥淚t contrasts with rates of improvement in farm livestock, with annual genetic change in growth of broilers and milk yields of cattle exceeding 1 per cent a year.鈥�
鈥淚 think that at best, very slow improvement in the primary trait of racehorses needs explanation by contrast with changes in other species,鈥� he says.
Journal reference: Biology Letters, DOI: 10.1098/rsbl.2015.0310
