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Good genes help racehorses to be winners

December 18, 2007 By Matt Kaplan This article courtesy of Nature News.

Study of stud horses reveals a significant role for genetics.

Does a racehorse’s success come from its genes? New research shows that genetics really do play an important part in whether a horse will be a winner or a loser on the racetrack. But it also hints that a high stud fee might not guarantee getting the good genes: horse breeders don't always get what they pay for.

Evolutionary ecologists Alastair Wilson and Andrew Rambaut at the University of Edinburgh in Scotland took a detailed look at the genetics of racehorses. They obtained data for the lifetime earnings of 554 currently or recently active stallions used for breeding, as well as the earnings of their ancestors going back several generations. This gave them a database of 4,476 horses going back to 1922, with full lifetime performance statistics for 2,500 of them. They used these data to model the estimated lifetime earnings of the children of the current studs.

They found that environmental factors such as training, diet, strategic race entry and jockey skill accounted for 91.5% of the variation in a horse's winnings and 8.5% of the effect was genetic. “8.5% may seem small, but for those of us studying the benefits generated by genetics in wild animals this is huge,” says Wilson.

In the wild, where environmental conditions vary a lot and survival can depend on luck as much as anything else, genetics usually account for about 1-2% of survival rates, says Wilson. But in the highly regulated environment of racehorses, where winning races is the main measure of success, genetics has a much bigger effect.

Getting what you pay for

The team also wanted to see if stud prices were indicative of genetics. These prices can vary wildly: mild-mannered stallions can cost hundreds of dollars, and stallions with grand reputations can cost millions.

In their sample, they report, the stud price was not linked to the success of the offspring. Amongst these horses, paying a few hundred to breed a mare with an average racing stallion was as good as paying a few million. “We expected stud fees to be honest signals [of success] but they were not,” says Wilson.

These findings might be skewed, says Larry Bramlage, an equine orthopaedic surgeon in Lexington Kentucky, because they look at studs with a mix of ages. Some are so young that their stud price depends solely on their own success (which is largely the result of environmental effects that can't be passed on to progeny), and some are old enough that their price is weighed entirely on the success of their offspring. The latter, he notes, is a much better measure of genetic quality, and most horse breeders know that.

“If you took the stud fees of stallions that had been breeding for at least ten years, I think you would get a very different result,” Bramlage says. In such a sample, he thinks genetics would link to price.

This is a fair point, says Wilson, and should be accounted for in future studies.


  1. Wilson, A. J. & Rambaut A. Biol. Lett. doi:10.1098/rsbl.2007.0588 (2007).


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