From a piece by Justin Petrone in BioArrayNews (my emphases):
… a group of researchers from horse-genetics firm Equine Analysis, the University of Kentucky, and the UK’s Royal Veterinary College used the EquineSNP50 to uncover significant inbreeding in thoroughbreds, especially during the past 15 years, a trend that the authors called “worrisome.”
The researchers genotyped 467 Thoroughbred horses born between 1961 and 2006 using the EquineSNP50. They determined that inbreeding in Thoroughbreds has increased over the past 40 years, with the majority of the increase in inbreeding found in cohorts born in 1996 and after, which, the authors note, coincides with the introduction of stallions covering larger numbers of mares.
According to the paper, all Thoroughbred horses that are alive today, estimated to number in the millions, are descended from three stallions and about 70 mares that were bred in England in the early 18th century. At the same time, breeding practices have evolved with the Thoroughbred horse over the past 50 years, as an emphasis changed from breeding “superior race horses” to siring as many foals as possible to sell, the authors wrote. They noted that 40 years ago, most stallions “covered,” or were mated with, a maximum of 40 mares a year, while many current stallions cover close to 200 mares. Breeding methods have changed too, with companies like Midway, Ky.-based Equine Analysis now offering genetic tests to identify animals that will race well.
The result of this shift toward breeding more animals from popular stallions has resulted in a decrease of genetic diversity, according to the authors, much of it taking place during the last decade, as the popular stallions covered more and more mares.
“It is worrisome that the increase in inbreeding that we observe is therefore not spread over a 40-year period but is concentrated in the period following the dramatic changes made to breeding practices in the mid-1990s,” the authors wrote. While they argued that the loss of genetic diversity identified in this study is not “excessive,” they said the trend is “worrisome.” The Thoroughbred industry “should not be complacent” and “continued monitoring of the situation is needed to ensure that recent major changes in breeding methods do not further negatively impact on this historic breed,” the authors wrote.
There’s a link to the paper here. Thanks to my brother for passing on horse genetics stories that don’t hit the equine headlines.