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  • Writer's pictureThe PFERA Team

Placing Limits to Preserve Breeds

The Jockey Club has recently announced that they will be looking into setting a limit on the number of mares a stallion can cover each breeding season. Currently, stallion books are closed based on the discretion of the managing team but for the future, The Jockey Club is proposing a 140 mare limit per stallion.


The main motivation behind the limit is to preserve genetic diversity and the breed itself. A small gene pool has consequences including deformities, low fertility, and genetic diseases. Contrary to a wild species whose main goal is survival, Thoroughbreds are bred for their athletic ability making these consequences detrimental. The sport of racing would suffer exponentially with a large decrease in the quality of horses being produced. A small gene pool contains too many similar sets of DNA, causing a decrease in variation and making gene mutations volatile. While it can be difficult to pinpoint where a condition originates, the racing industry has already seen an increase in the number of orthopaedic and lung issues amongst its horses.


Thoroughbred stallions will be gradually grandfathered into the new limit. Those entering the stud book in 2020 will be exempt from the limit through 2023. Stallions entered in 2019 will be exempt through the 2022 season, 2018 stallions through 2021and 2017 stallions will be required to abide by the 140 mare cap as of January 1st, 2020 (Paulick Report, 2019).

A positive example of breeding limits can be seen by looking at the Standardbred industry who set a 140 mare limit for their stallions beginning in 2009. The Standardbred industry was grappling with the same issues when they realized hundreds of mares were visiting the same group of stallions year after year, indicating that down the line, inbreeding would become a large issue. With the threat of the Standardbred breed becoming less diverse, USTA officials put the breeding limit in place and for the most part, it has been well received. The majority of the industry has been able to put the long term success of the Standardbred breed ahead of short term financial gain.

Continuing scientific research on this issue is in the best interest of The Jockey Club and the sport itself. The opportunity to completely map equine genomes will provide better insight into which crosses would cause issues and should therefore be avoided. Until then, limiting the number of mares a stallion can breed is a positive measure to encourage gene diversity.

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