Fall in number of stallions used by US Thoroughbred breeders

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The number of stallions used to produce last year’s Thoroughbred foals in the United States fell 8.3 percent, according to the Jockey Club.

The Jockey Club, which is the keeper of the American Stud Book, has just announced the 2018 breeding statistics, a month after it indicated it was 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.

The Jockey Club said 1630 stallions covered 32,508 mares in North America during 2018, according to statistics compiled up to September 26, 2019. These breedings have resulted in 20,363 foals of 2019 being reported to the Jockey Club on Live Foal Reports.

The Jockey Club estimates that the number of live foals reported so far is about 90 percent complete.

The reporting of live foals of 2019 is down 3.6 percent from last year at the same time, when the organisation had received reports for 21,130 live foals of 2018.

In addition to the 20,363 live foals of 2019 reported through to September 26, the club also received 2405 No Foal Reports for the 2019 season.

Ultimately, the 2019 registered foal crop is projected to reach 20,800.

The top 10 states and provinces ranked by number of state/province-sired live foals of 2019 reported through to September 26, 2019.

The number of stallions declined 8.3 percent from the 1778 reported for 2017 at this time last year, while the number of mares bred declined 5.2 percent from the 34,288 reported for 2017.

Kentucky annually leads all states and provinces in terms of Thoroughbred breeding activity. Kentucky-based stallions accounted for 53.7 percent of the mares reported bred in North America in 2018 and 59.9 percent of the live foals reported for 2019.

The 17,446 mares reported bred to 241 Kentucky stallions in 2018 have produced 12,200 live foals, a 1.4 percent decrease on the 12,370 Kentucky-sired live foals of 2018 reported at this time last year.

The number of mares reported bred to Kentucky stallions in 2018 increased 0.3 percent compared to the 17,401 reported for 2017 at this time last year.

Among the 10 states and provinces with the most mares covered in 2018, three produced more live foals in 2019 than in 2018 as reported at this time last year: California, Louisiana, and Maryland.

The national statistics include 303 progeny of stallions standing in North America but foaled abroad, as reported by foreign stud book authorities at the time of publication.

The club’s board of stewards, in announcing a month ago it was considering phasing in a cap of 140 mares bred per individual stallion per year, invited feedback on the proposal.

The size of the North American Thoroughbred foal crop has diminished significantly over the years, from 37,499 in 2007 to little more than 20,000 estimated for 2020.

The latest breeding statistics released include 303 progeny of stallions standing in North America but foaled abroad, as reported by foreign stud book authorities.

While the US thoroughbred foal crop is down, the number of stallions breeding more than 140 mares in a season has grown, leading to concerns around the narrowing of diversity.

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 before 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.

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