Breeding racehorses: what price good genes?

Wilson AJ & Rambaut A

(2008) Biology Letters 4, 173-175.

Horse racing is a multi-million pound industry, in which genetic information is increasingly used to optimize breeding programmes. To maximize the probability of producing a successful offspring, the owner of a mare should mate her with a high-quality stallion. However, stallions with big reputations command higher stud fees and paying these is only a sensible strategy if, (i) there is a genetic variation for success on the racecourse and (ii) stud fees are an honest signal of a stallion's genetic quality. Using data on thoroughbred racehorses, and lifetime earnings from prize money (LE) as a measure of success, we performed quantitative genetic analyses within an animal model framework to test these two conditions. Although LE is heritable (VA=0.299±0.108, Pr=0.002), there is no genetic variance for stud fee and the genetic correlation between traits is therefore zero. This result is supported by an absence of any relationship between stud fees for currently active stallions and the predicted LE for their (hypothetical) offspring. Thus, while there are good genes to be bought, a stallion's fees are not an honest signal of his genetic quality and are a poor predictor of a foal's prize winning potential.

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Andrew Rambaut, 2007