Thoroughbred stallions born in the United States from 2020 will be allowed to cover only 140 broodmares a year, the Jockey Club has announced.
The club has adopted a new rule around breeding in response to concerns around the narrowing of the diversity of the Thoroughbred gene pool in the US.
The size of the North American Thoroughbred foal crop has diminished significantly, from 37,499 in 2007 to about 20,500 estimated for 2020.
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 issue gave rise to a proposal last September that top stallions be limited in the number of mares they could serve in a season.
The Jockey Club board of stewards announced last week that it has adopted a final rule, reflecting the club’s goal to preserve the health of the Thoroughbred breed for the long term.
Under the rule, the total number of broodmares bred per individual stallion whose year of birth is 2020 or thereafter shall not exceed 140 per calendar year in the United States, Canada, and Puerto Rico.
The club will limit the number of Stallion Service Certificates for such stallions to a maximum of 140 per calendar year.
For stallions born in 2019 and earlier, there will be no limit to the number of mares reported bred in the United States, Canada, and Puerto Rico.
The club said it received many thoughtful comments in response to its September rule proposal.
It said the stewards carefully considered those comments in formulating the rule change.