Jockey Club floats proposal to limit stallion books

By: Tom LaMarra

Posted: Sept. 6, 2019

In a major announcement, The Jockey Club Board of Stewards Sept. 6 said it is considering a limit on the number of mares that can be bred to individual stallions to 140 under a phased-in approach.

The Jockey Club cited concern “with the narrowing of the diversity of the Thoroughbred gene pool” as the reason for the proposal which, if enacted, with begin with the 2021 breeding season. The Jockey Club is the keeper of the American Stud Book and maintains the Principal Rules and Requirements of the American Studbook in order to ensure the welfare of the Thoroughbred breed.

The size of the North American foal crop has diminished significantly, from 37,499 in 2007 to the 20,500 estimated for 2020, The Jockey Club noted. In 2007, 37 stallions reported in excess of 140 mares bred each from a total of 3,865 stallions. By 2010 that number had declined to 24. Since then, the number has jumped 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.

In 2007, 5,894 mares (9.5% of the total) were bred by stallions that covered more than 140 mares. By 2019, 7,415 mares (27% of the total) were covered by stallions with books of more than 140.

“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 organization said.

The proposed phase-in is 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 Jan. 1, 2021.

“The stewards will continue to study the decreasing diversity of the Thoroughbred gene pool and its cause and potential effects over the course of time,” The Jockey Club said. “As more data and analyses become available, the stewards may revise The Jockey Club’s approach to protecting the breed’s health and welfare.”

Comments on the proposal can be submitted through The Jockey Club website.