Ageing Thoroughbred parents take edge off offspring’s speed – study

Researchers analysed more than 900,000 race performances from more than 100,000 racehorses from races across Great Britain.
Image by Peter W

Parental age in Thoroughbreds can be a determining factor in who comes out on top in horse races, researchers report.

Experts from the University of Exeter in England have shown that the speed of Thoroughbred horses declines as parental age at conception increases.

The research team analysed more than 900,000 race performances from more than 100,000 racehorses from races across Britain.

They found that the age of both the mothers and fathers of the horses played a significant role in the overall speed of the racehorses.

The researchers believe the study findings, reported in the journal Royal Society Open Science, can play a pivotal part not only in optimising racehorse breeding, but crucially offers further evidence that parental age can affect offspring characteristics.

“The fact that parental age affects racehorse speed should be of interest to the horseracing industry,” said Dr Patrick Sharman, a postdoctoral research associate (visiting) from the Centre for Ecology and Conservation at the University of Exeter’s Penryn Campus in Cornwall.

“More generally, it adds to an increasing body of evidence which points towards parental ‘state’ at the time of conception having an influence on offspring phenotype. This would have implications well beyond racehorses and the horseracing industry.”

The effects that parental age can have on the characteristics of their offspring have been studied in several species in recent years. However, this is the first in-depth study which attempts to estimate maternal and paternal age effects specifically for speed in thoroughbred horses.

The study analysed data from almost 25 years of racing results from meetings across Britain, from 1996-2019. Their data included the offspring of 41,107 mothers and 2887 fathers. They found a significant effect of maternal age on speed, with each additional year of age at conception decreasing the offspring’s speed by 0.017 yards per second.

Whilst this may sound modest, it actually converts into a predicted difference of about one second over a race of one mile between, by way of example, a five-year-old and a 15-year-old mother. Intriguingly, the paternal age also showed a decrease of 0.011 yards per second for every increasing year in stallion age – a key finding since thoroughbred stallions play no active involvement in parental care.

Dr Sharman added: “It is perhaps not surprising that offspring speed declines with increasing maternal age. It is the dams, after all, who care for the foal, first in utero, and then through to around 6 months of age.

“What I find fascinating, though, is that increasing paternal age also causes a significant decline in racehorse speed. Thoroughbred stallions play no part whatsoever in raising a foal, so what is behind this decline in speed?”

The team says that further research is now required to determine the mechanisms underlying this phenomenon.

» Further reading: Separating fact from myth: True worth of aged Thoroughbred broodmares revealed

Sharman, Patrick; Young, Andrew J; and Wilson, Alastair J.
Evidence of maternal and paternal age effects on speed in thoroughbred racehorses
R. Soc. open sci.9220691220691

The study, published under a Creative Commons License, can be read here

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