'There is a serious concern for the narrowing genetic diversity of the breed'

Several supporters of The Jockey Club rule to cap the mares bred per stallion annually to head off potential deleterious effects from a shrinking gene pool said they understood the February 17 decision to rescind the rule but added they are concerned because the threat facing the breed's health remains.

"I'm not sure of the next step but we are still left with the problem The Jockey Club attempted to alleviate, which is that there is a serious concern for the narrowing genetic diversity of the breed," said Walker Hancock, president of Claiborne Farm.

"I think it's worthy to continue to have an open conversation with all stakeholders on how we go about fixing this issue, which might not be serious currently, but will be a dire problem 20-plus years into the future if nothing changes."

In September 2019, The Jockey Club first proposed capping the number of mares bred per year to 140 and solicited comments from the breeding community.

Along with this proposal, The Jockey Club reported that 37 North American stallions in 2007 bred books in excess of 140 mares out of a total of 3,865 stallions. Since 2010, the number has nearly doubled to 43 sires out of a stallion population that is less than half the size of the population in 2007.

On the mare side in 2007, according to The Jockey Club, 5,894 mares (9.5 per cent of all mares bred) were bred by stallions that covered more than 140 mares. By 2019, 7,415 mares (27 per cent of all mares bred) were covered by stallions with books of more than 140, a threefold increase.

Based on a majority of support expressed during the comment period, The Jockey Club implemented the rule in May 2020. The cap took affect with the colts born in 2020 or later and did not apply to stallions born in 2019 or earlier.

"The stewards carefully considered those comments in formulating a rule that will promote diversity of the thoroughbred gene pool and protect the long-term health of the breed," said The Jockey Club in a statement announcing the new rule.

The mare cap had its opponents and they argued in a lawsuit filed in February 2021 that the rule change was "arbitrary" and "anti-competitive" and would reduce access or drive up prices for many owners of mares looking to access top stallions.

The suit also contended that the rule risked driving the best stallions overseas as no other country with a thoroughbred stud book imposes a cap. The lawsuit was filed in Kentucky by Spendthrift Farm, Ashford Stud (under the name Bemak N.V.) and Three Chimneys Farm.

The Kentucky General Assembly weighed in on the rule by filing a House bill on February 14 that would prohibit any registrar from capping the number of mares bred per year or refusing to register any foals based on the number of mares bred.

It would also task the Kentucky Horse Racing Commission to "select and utilise an entity to serve as the registrar of thoroughbreds" and submit to the jurisdiction of Kentucky and its laws. The bill was co-sponsored by Speaker of the House Rep. David Osborne, an owner-breeder from Prospect, Kentucky, and Rep. Matthew Koch, the owner of Shawhan Place near Paris, Kentucky.

Rule rescinded

Three days after the bill was filed, The Jockey Club chose to rescind the rule.

"It would have been a very disruptive path to go down," said Bill Farish with Lane's End Farm and an ardent supporter of the rule about continuing to fight the legislation.

"There are bigger issues at the moment, such as the Horseracing Integrity and Safety Authority (Hisa), that can hopefully turn into huge wins for the industry in the long run for integrity and safety. The Jockey Club made the decision to pursue those issues more instead of going down this road with the legislators.

"There are so many positive things going on with racing right now, with the purse structure and yearling prices and the sales overall," he continued.

"If we could have had this and seen Hisa through to the end, a lot of our woes as an industry would have been taken care of. As it is, the number of Kentucky stallions is down 57 per cent from what it was 30 years ago and that is not good economically for the state. I don't think these kinds of issues were ever discussed by the legislators."

Because the lawsuit filed by the three farms is still pending, The Jockey Club refrained from commenting on its decision-making process in connection with the mare cap rule.

"We note that there is a wealth of information available identifying the continued narrowing of the North American thoroughbred gene pool, much of which was identified by The Jockey Club executive vice-president and executive director Matt Iuliano in his comments within the September 2019 issue of the BloodHorse," said Jim Gagliano, president and chief operating officer for The Jockey Club.

"Furthermore, the fact that the gene pool continues to narrow was further confirmed by more recent research, which was presented in the study titled 'Genomic inbreeding trends, influential sire lines, and selection in the global thoroughbred horse population.'"

Several inbreeding analyses have raised concerns about decreasing genetic diversity in thoroughbreds.

Increases in inbreeding lead to an increase in "mutational load," which is associated with a general decrease in genetic quality and exposes the breed to undesirable traits in performance and/or production, according to Dr Bob Losey in an inbreeding analysis he co-authored with Dr Thomas Lambert for the University of Louisville. Using their own scoring system, Losey and Lambert documented a moderate rise in inbreeding among stallions listed in the BloodHorse Stallion Register between 2000 and 2020.

A 2011 study done by Dr Matthew Binns and Dr Ernie Bailey showed a marked increase in inbreeding that corresponded with the rise of books with 100 or more mares.

"It is worrisome that the increase in inbreeding that we observe is there, not spread out over a 40-year period, but is concentrated in the period following the dramatic changes made to breeding practices in the mid-1990s," the study states.

The study's conclusions also noted that the loss of genetic diversity observed is not excessive but still found the sharp rise over the ten-year period a concern.

The 'Global inbreeding trends' study cited by Gagliano was published in 2020 by Dr Beatrice McGivney and six other researchers, including Dr Emmeline Hill, whose research identified the myostatin "speed gene" that indicates a propensity toward sprinting or staying. The study looked at the diversity of genetic samples from 10,118 thoroughbreds in Australia, New Zealand, Europe, Japan, North America and South Africa from 1970-2017.

"In the most comprehensive genetic analysis performed in this population we show a striking temporal increase in inbreeding and regional variance across the global thoroughbred population during the last five decades," the study said.

"Expansion of the timeline to include the most recent decade using a sample size more than 20-fold larger indicates that despite industry cognisance of inbreeding and previous cautions, there has been no arrest in the rate of increase in inbreeding and it is a global, population-wide phenomenon."

Mendelssohn, the son of Scat Daddy and half-brother to Into Mischief and Beholder, at Ashford Stud, where he had a book of 197 mares in 2021Credit: Michele MacDonald

Owner-breeder Carrie Brogden with Machmer Hall said she could see the warning flags when reviewing the 2021 Report of Mares Bred for North America that showed the top 16 stallions by number of mares bred included three-time leading North American sire Into Mischief (214 mares bred), five of his sons - Goldencents (230), Authentic (229), Practical Joke (223), Instagrand (190) and Audible (189), and Into Mischief's half-brother Mendelssohn (197).

"Into Mischief is only 17 years old. What on earth is going to happen in ten years?" she asked.

The Standardbred breeding industry wrestled with inbreeding concerns about 14 years ago and asked Dr Gus Cothran with the University of Kentucky's Gluck Equine Research Center to do a trend analysis of heterozygosity for Standardbreds. Heterozygosity refers to degree of genetic variation associated with a given trait or characteristic.

In Standardbreds, the potential for breeders to focus on a narrower group of stallions was magnified by the permission of artificial insemination.

"He found we were indeed losing genetic diversity," said Russell Williams, US Trotting Association president and president/CEO of Hanover Shoe Farms. "We worked out a book limit with Dr Cothran and he cautioned us to continue monitoring to be sure the limit was appropriate."

The USTA adopted a 140-mare cap in 2009. Armed with Cothran's research and a potentially troublesome trend seen with certain stallions' progeny showing a propensity toward developing osteochondritis dissecans lesions (known more commonly as OCDs), the USTA got a buy-in from most breeders for the mare cap, according to Williams.

The mare cap was challenged in court and the USTA prevailed because it showed the restriction was a "rule of reason" and not adopted for commercial reasons.

A follow-up genetic study to evaluate the impact of the cap is ongoing, with the results not anticipated for another year.

"I think there will be some revelations from this study but I don't think we will see anything to indicate we were wrong to do what we did," said Williams. "We'll see once we get the final report, but if I have any concerns right now it would be that our number (the cap) was too high."

Bob Brady, the owner of Kentuckiana Farms near Lexington, which co-owns 2021 Horse of the Year Test Of Faith, said the mare owners and stallion farms have long adjusted to the mare cap, and he believes the breed is better for it.

"We were backing ourselves into a corner," he said. "I think the cap has opened some avenues for other stallions to get a chance at stud. We also have an influx of semen from Europe, which will greatly expand our genetic base, so I think the goal has been achieved.

"We know the mare cap was a move in the right direction, and it's basically had little impact on our operation."

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