Like many trends in racing and breeding over the last 30 years, the concentration of the gene pool through a relatively small group of stallions has not been a healthy development for the thoroughbred breed.

That’s the view taken by The Jockey Club of the United States when it announced recently that it is considering a rule setting a cap of 140 mares bred per stallion during a calendar year. The rule, if adopted, would be phased in over three years, beginning in 2021.

This concentration of bloodlines has occurred primarily because of two significant changes in the breeding industry. The first is the diminishing size of the foal crop in North America, which peaked at 51,296 in 1986 and has been estimated by The Jockey Club to be 20,500 in 2020. That’s a decline of 60 per cent in 34 years. From 2007 to 2020 alone, the foal crop has declined by 45 per cent from 37,499 to 20,200.

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