STUDY: Consolidation of sire lines among leading Thoroughbred stallions

The landscape of Thoroughbred breeding in the United States has changed since the turn of the century.

According to data from The Jockey Club Fact Book, the number of stallions standing at stud in the United States has fallen from 4,250 in 2001 to 854 in 2024, an 80% decrease. Even in Kentucky, the epicenter of the U.S. Thoroughbred breeding industry, the number of stallions has fallen 56% from 449 in 2001 to 196 in 2024.

At the same time, the number of mares the average stallion covers has increased 113% from 14 in 2001 to 29.8 in 2024. In Kentucky, this metric has increased 88% from 45.2 in 2001 to 85 in 2024.

Many of today’s leading stallions descend from just three sire lines: the Mr. Prospector line, the Northern Dancer line, and the Bold Ruler line. With fewer stallions covering a higher number of mares on average, it’s fair to wonder about the impact on the U.S. Thoroughbred gene pool. Are other sire lines being crowded out by the dominance of the “big three” among leading stallions?

A statistical study can reveal the answer.

Consolidation of sire lines among leading stallions: research methodology

For the purposes of this study, our definition of a “leading stallion” is a stallion who achieved a top-five ranking on the list of leading North American sires by progeny earnings compiled annually by Bloodhorse.com.

We have charted every stallion who reached this success measure between 2001 and 2024. Then we grouped the stallions into two categories: those who achieved top-five rankings from 2001-2012 and those who achieved top-five rankings from 2013-2024. We then analyzed the pedigrees of the stallions in both categories to group them by sire line and determine the extent of consolidation from one 12-year period to the next.

Consolidation of sire lines among leading stallions: data analysis

First, let’s review the top five leading sires by progeny earnings each year from 2001-2012 and from 2013-2024:

From 2001-2012, a total of 23 stallions managed to achieve a top-five ranking by progeny earnings. From 2013-2024, a similar number of stallions (21) reached the same standard of success.

But upon grouping these stallions by sire line, it’s clear the 23 stallions from 2001-2012 represented a more diverse swath of sire lines than the 21 stallions from 2013-2024. Let’s examine the 2001-2012 groupings first:

2001-2012

Mr. Prospector
Distorted Humor (Forty Niner)
Elusive Quality (Gone West)
Empire Maker (Fappiano)
Speightstown (Gone West)
Smart Strike
Thunder Gulch (Gulch)

Northern Dancer
Dehere (Deputy Minister)
El Prado (Sadler's Wells)
Giant's Causeway (Storm Cat)
Langfuhr (Danzig)
Storm Cat (Storm Bird)

Bold Ruler
A.P. Indy
Malibu Moon (A.P. Indy)
Tapit (A.P. Indy)

Hail to Reason
Dynaformer (Roberto)
Kris S. (Roberto)
Saint Ballado (Halo)

Damascus
Fly So Free (Time for a Change)

In Reality
Tiznow (Relaunch)

Nasrullah
Rahy (Blushing Groom)

Nearctic
Wild Again (Icecapade)

Raise a Native
Maria's Mon (Majestic Prince)

Ribot
Pleasant Tap (His Majesty)

From 2001-2012, six leading stallions (26%) hailed from the Mr. Prospector sire line. They came from several branches of the line: through Forty Niner, Gone West, Fappiano, and Gulch. One leading sire, Smart Strike, was a son of Mr. Prospector.

Five leading stallions (22%) came from the Northern Dancer sire line. These five stallions came from four different branches: Deputy Minister, Sadler’s Wells, Danzig, and Storm Cat, with Storm Cat himself (from the Storm Bird branch) appearing among the leading sires on two occasions.

The Bold Ruler sire line was represented by three stallions (13%). One was A.P. Indy, and the other two were sons of A.P. Indy.

Three stallions (13%) came from the Hail to Reason sire line, two through Roberto and one through Halo.

Six other sires lines—Damascus, In Reality, Nasrullah, Nearctic, Raise a Native, and Ribot—were represented by one stallion (4%) apiece. It should be noted that Nasrullah was the sire of Bold Ruler, and Raise a Native the sire of Mr. Prospector, so Rahy (through Blushing Groom) and Maria’s Mon (through Majestic Prince) represent different branches of the broader Nasrullah/Raise a Native sire lines than Bold Ruler and Mr. Prospector.

Now let’s review the 2013-2024 leading stallions grouped by sire line:

2013-2024

Mr. Prospector
Candy Ride (Fappiano)
City Zip (Carson City)
Curlin (Smart Strike)
Gun Runner (Fappiano)
Pioneerof the Nile (Fappiano)
Quality Road (Gone West)
Speightstown (Gone West)
Unbridled's Song (Fappiano)

Northern Dancer
Giant's Causeway (Storm Cat)
Into Mischief (Storm Cat)
Justify (Storm Cat)
Kitten's Joy (Sadler's Wells)
Medaglia d'Oro (Sadler's Wells)
Scat Daddy (Storm Cat)
War Front (Danzig)

Bold Ruler
Constitution (A.P. Indy)
Malibu Moon (A.P. Indy)
Mineshaft (A.P. Indy)
Tapit (A.P. Indy)
Tonalist (A.P. Indy)

Caro
Uncle Mo (In Excess)

The difference is stark. Eight stallions (38%) represent the Mr. Prospector sire line, which increased its share of leading stallions by 46% from 2001-2012 to 2013-2024. Yet these eight stallions hailed from only four branches of the line (Fappiano, Carson City, Smart Strike, and Gone West), down from five branches in the 2001-2012 sampling.

The Northern Dancer sire line turned up seven leading stallions (33%), a 50% increase from the 22% of leading sires from 2001-2012. These seven stallions represent only three branches (Storm Cat, Sadler’s Wells, and Danzig), down from four branches in the 2001-2012 grouping.

Five stallions (24%) represented the Bold Ruler sire line, an 85% increase in its share of leading stallions. As in 2001-2012, all these stallions descended from the A.P. Indy branch.

The Damascus, In Reality, Nearctic, and Ribot sire lines disappeared entirely. So too did the non-Mr. Prospector branch of the Raise a Native sire line.

Only one sire line outside the big three was represented among the leading sires of 2013-2024: the Caro Line, via Uncle Mo. Caro is a great-grandson of Nasrullah, so he represents a different branch of the Nasrullah line than Bold Ruler.

Conclusions

The number of sire lines represented among leading U.S. stallions decreased by 60% from 10 in 2001-2012 to only four in 2013-2024.

At the same time, the big three sire lines of Mr. Prospector, Northern Dancer, and Bold Ruler grew their shares of the market by an average of 60%. From 2001-2012, these three sire lines yielded 61% of leading sires. That percentage jumped to 95% over the course of 2013-2024, an increase of 56%.

Non-big-three sire lines produced 39% of leading sires during the 2001-2012 timeframe. This fell to just 5% from 2013-2024, an 87% decrease.

The reasons for these shifts can be debated and are likely numerous and nuanced. But the data is stark: the diversity of sire lines represented among North America’s leading stallions by progeny earnings has decreased sharply since the turn of the century, consolidating almost entirely into the Mr. Prospector, Northern Dancer, and Bold Ruler sire lines.