The Jockey Club explores the limits of pound size



The Jockey Club Board of Directors, concerned about the reduction in the diversity of the thoroughbred gene pool, announced on September 6 that it was considering rules to limit the annual breeding of individual stallions starting in the season. breeding 2021.

The Jockey Club, established in 1894, is the custodian of the American Stud Book and maintains the main rules and requirements of the American Studbook to ensure the welfare of the Thoroughbred breed. The size of North American foal production has declined significantly, from 37,499 in 2007 to an estimated 20,500 for 2020.

In 2007, 37 stallions would have more than 140 bred mares, out of a total of 3,865 stallions. By 2010 the number of stallions with 140 or higher mares had fallen to 24, but since then their number has almost doubled to 43 stallions out of a stallion population that is now less than half of that of 2007.

As for mares, in 2007, 5,894 mares (9.5% of the total) were bred by stallions that covered more than 140 mares. In 2019, 7,415 mares (27% of the total) were covered by stallions with pounds over 140, a threefold increase.

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

The Jockey Club Board of Directors envisions a cap of 140 mares bred per individual stallion per calendar year in North America, progressively, as follows:

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

Stewards will continue to study the decreasing diversity of the thoroughbred gene pool, as well as its cause and potential effects over time. As more data and analysis becomes available, Stewards may revise the Jockey Club’s approach to protecting the health and welfare of the breed.

The Jockey Club invites and welcomes comments on the proposed rule from breeders, owners and others interested in the Thoroughbred breed and the industry. Contact the Jockey Club at



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