The offspring of expensive stallions owe their success more to how they are reared, trained and ridden than good genes, a study has found.
Breeders are prepared to spend vast sums on trusted stallions
Only 10% of a horse's lifetime winnings can be attributed to their bloodline, research in Biology Letters shows.
Edinburgh scientists compared the stud fees, winnings and earnings of more than 4,000 racehorses since 1922.
They found that the vast sums breeders are prepared to pay for top stallions do not guarantee the best genes.
The research was carried out by evolutionary biologists Alastair Wilson and Andrew Rambaut at the University of Edinburgh.
They found that while there was genetic variance in the quality of stallions at stud, this was not reflected in the size of the horse's stud fee.
"There are good genes out there to be bought but they don't necessarily come with the highest price tag," Dr Alastair Wilson told the BBC News website.
"It seems much more likely that people who can afford to pay high stud fees can also afford to manage and train their horses well."
The offspring of expensive stallions did tend to win more over their lifetime, he said, but genes played only a small role.
By far the biggest factor was the horse's environment - the way they were trained, the choice of races entered and which jockeys were employed, Dr Wilson added.
The findings may have parallels in the natural world, he added, in how signals of male genetic quality - such as the size and shape of a peacock's tail - are used by females to select a mate.
In this context, where the breeder was selecting the horse, fees paid for a stallion were not an honest signal of genetic quality, the researchers said.
Full details of the research are published in the Royal Society journal Biology Letters.