Sex lives of the most popular US Thoroughbreds may be curbed

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Still from “From Yesterday to Today: A Celebration of The Jockey Club’s 125th Anniversary”.
 © Jockey Club

The Jockey Club in the United States is looking to curb the sex life of the country’s most popular Thoroughbred stallions.

The organisation is considering a cap on the number of breedings allowed for any single stallion in a calendar year.

The rule is being proposed in response to concerns around the narrowing of the diversity of the Thoroughbred gene pool in the US.

Its board of stewards is looking at phasing in a cap of 140 mares bred per individual stallion per year.

The Jockey Club, established in 1894, is the keeper of the American Stud Book and maintains the related rules and requirements in order to ensure the welfare of the Thoroughbred breed.

The size of the North American Thoroughbred foal crop has diminished significantly, from 37,499 in 2007 to the 20,500 estimated for 2020.

Fewer thoroughbred foals are expected to be born in the US in the coming season.
The US thoroughbred foal crop is down but the number of stallions breeding more than 140 mares in a season has grown, leading to concerns around the narrowing of the diversity of the gene pool.

In 2007, 37 stallions reported in excess of 140 mares bred each from a total of 3865 stallions. By 2010, that number had declined to 24.

Since then, the number has nearly doubled to 43 stallions reporting 140 or more mares bred from a population of stallions that now stands at less than one-half that of 2007.

On the mare side, in 2007, 5894 mares (9.5% of the total) were bred by stallions who covered more than 140 mares. By 2019, 7415 mares (27% of the total) were covered by stallions with books of more than 140, a threefold increase.

The combination of these changes has resulted in a substantial increase in the percentage of foals produced by a discreet segment of stallions, signaling a worrisome concentration of the gene pool.

The phase-in of the cap is proposed as follows:

  • Stallions entering stud service for the first time in 2020 would be exempt from the 140 limit through the 2023 season;
  • Stallions that entered stud service in 2019 would be exempt through the 2022 season;
  • Stallions that entered stud service in 2018 would be exempt through the 2021 season;
  • Stallions that entered service in 2017 or prior would be subject to the 140 cap as of January 1, 2021.

The stewards say they will continue to study the decreasing diversity of the Thoroughbred gene pool and its cause and potential effects over the course of time.

As more information becomes available, they may revise the club’s approach to protecting the breed’s health and welfare.

The organisation says it welcomes comments on the proposed rule from breeders, owners, and others with interests in the Thoroughbred industry.

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