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Racehorse Pedigrees and Bloodlines: Unlocking the Secrets

Last updated: May 10, 2023

By: Miles HenryFact Checked

My family wonders why I study a horse’s bloodline so intensely before attending an auction. They see it as a hobby, but for me, it’s more than that; it’s an opportunity to understand racehorse pedigrees and the potential they hold for future champions.

Learning how a horse’s lineage can influence its racing performance and, consequently, its value has since become a passion of mine. It’s a skill that takes time to master, but it’s one I’m eager to share with others.

In this blog post, we will embark on a journey to explore the importance of racehorse pedigree and bloodlines in the racing industry. We will delve into the basic concepts, famous bloodlines, and breeding strategies that contribute to creating successful racehorses. Join me as we unravel the mysteries of racehorse genetics and discover the secrets behind the champions of the track.

Basic Concepts and Terminology

Mastering the terminology and fundamental concepts is crucial when exploring the world of horse pedigrees. By breaking down the essentials, I aim to help you navigate the intricate details of racehorse pedigree and bloodlines more effectively.

A. Definition of racehorse pedigree: A racehorse’s pedigree is essentially its family tree, documenting the horse’s ancestry and lineage. It provides valuable information on the horse’s parents, grandparents, and even great-grandparents, revealing the genetic makeup that influences its abilities and potential on the racetrack.

B. Definition of bloodlines: Bloodlines refer to the specific family lines within a breed that are known for their desirable traits and successful racing performance. By tracing the bloodlines, breeders, and enthusiasts can identify horses with a strong racing heritage, often leading to more consistent results on the track.

C. Key terms used in racehorse breeding: When discussing racehorse breeding, it’s important to be familiar with some essential terms:

  1. Sire – The male parent of a horse or the father.
  2. Dam – The female parent of a horse or the mother.
  3. Grandsire – The sire of the sire or dam, essentially the horse’s grandfather.
  4. Broodmare – A female horse primarily used for breeding purposes.
  5. Stallion – A male horse used for breeding.
  6. Foal – A young horse, typically under one year old.
  7. Colt – A male horse under the age of four.
  8. Filly – A female horse under the age of four.

Knowing these words helps you find your way through the world of racehorse pedigrees and bloodlines easily. This way, you can make better choices about breeding, prices, and racing horses in general.

northern dancer granddaughter edited
Skim Milk. Northern Dancer is both her great-grandfather and great-great-grandfather. By: Rennett Stowe

The Role of Bloodlines in Racing Performance

Now, let’s talk about how a racehorse’s family tree affects how well they do in races. This is an important part of understanding pedigrees and bloodlines in the world of Thoroughbred racing.

The Influence of Genetics on a Racehorse’s Performance

Genetics is the study of how traits are passed from parents to their offspring. In living organisms, including horses, genes are small units carrying information needed for growth and development. When a baby horse (foal) is born, it inherits half of its genes from its mother (the dam) and half from its father (the sire). These genes determine the foal’s appearance, behavior, and abilities.

In racehorses, genetics plays a crucial role in speed, endurance, and overall performance on the track. Understanding genetics helps us learn more about the traits that contribute to a racehorse’s success and how these traits are passed down through generations. This knowledge aids breeders in selecting the best combinations of sires and dams to produce successful racehorses.

When I first started learning about racehorses, I quickly discovered that by carefully examining a horse’s bloodline, it’s possible to identify potential strengths and weaknesses that can impact their success on the racetrack.

Balancing inbreeding and outcrossing for optimal genetic diversity

Another crucial aspect of breeding strategies for success is striking a balance between inbreeding and outcrossing. Inbreeding can help preserve desirable traits and maintain successful bloodlines. However, it can also lead to a higher risk of genetic disorders and a decrease in overall genetic diversity.

On the other hand, outcrossing involves breeding horses from unrelated bloodlines, which can help maintain genetic diversity and reduce the risk of inherited health issues. To achieve optimal results, breeders must find a balance between preserving the desired traits from successful bloodlines and maintaining genetic diversity.

This can involve carefully selecting breeding partners that share a desirable trait but are not too closely related or introducing new bloodlines to refresh the gene pool. By adopting these strategies, breeders can work towards producing healthy, high-performing racehorses with the potential for success on the track.

Famous Racehorse Bloodlines and Ancestors

Let’s take a look at some famous racehorse families and their ancestors. These special bloodlines have produced many successful racehorses throughout history, and knowing about them can help us understand what makes a great racehorse.

Painting of the foundation sire Byerley Turk.
Byerley Turk

Key Thoroughbred Foundation Sires

During my exploration of racehorse pedigrees, I was fascinated to learn that almost all modern Thoroughbreds can trace their lineage back to three foundation sires: the Darley Arabian, the Byerley Turk, and the Godolphin Arabian.

These stallions, imported to England in the late 17th and early 18th centuries, played a crucial role in shaping the Thoroughbred breed and establishing the bloodlines that continue to dominate the racing world today.

The descendants of these foundation sires have gone on to achieve remarkable success on the racetrack. Some of the most famous racehorses in history, such as Man o’ War, Secretariat, and Seabiscuit, can trace their lineage back to these influential ancestors.

By understanding the accomplishments of these legendary horses, we can better appreciate the impact that bloodlines have on racing performance and the continued quest for excellence.

Pioneering Sires of the 20th Century

These exceptional sires played a pivotal role in shaping the landscape of modern Thoroughbred racing. With their remarkable bloodlines and lasting legacies, their contributions continue to influence the success of today’s racehorses.


Phalaris was foaled in 1913; he was particularly known for his speed, which he passed on to his descendants. Among his successful progeny are Pharos and Sickle, who went on to become important sires themselves.

Phalaris’ impact on Thoroughbred racing cannot be overstated. His influence is evident in the success of countless champions throughout the years. To illustrate just how significant his legacy is, consider the leading sire’s list by earnings for 2021.

All but one of the top 50 stallions on that list can trace their bloodlines back to Phalaris. This remarkable statistic highlights the enduring presence of Phalaris in the pedigrees of today’s top racehorses.

Phalaris’ influence can be seen in many modern racing champions through his descendants. Some notable examples include:

  1. Nasrullah – A grandson of Phalaris through his sire Nearco, Nasrullah sired Bold Ruler, who in turn sired the legendary Secretariat.
  2. Northern Dancer – A great-grandson of Phalaris through his dam, Natalma, who was a granddaughter of Phalaris. Northern Dancer became one of the most influential sires of all time, with his progeny including Nijinsky, Sadler’s Wells, and Galileo.
  3. Raise a Native – A great-grandson of Phalaris through his sire, Native Dancer. Raise a Native’s descendants include Mr. Prospector and Alydar, who went on to produce successful racehorses like Fusaichi Pegasus, Smarty Jones, and Afleet Alex.
  4. Seattle Slew – A great-great-grandson of Phalaris through his sire, Bold Reasoning, who was a grandson of Bold Ruler. Seattle Slew, the 1977 Triple Crown winner, went on to sire successful racehorses like A.P. Indy, Slew o’ Gold, and Swale.
Picture of the great racehorse Man o' War.
Man o’ War

Man o’ War

Man o’ War, a legendary racehorse in his own right, became an influential sire after his retirement. Among his most successful progeny were War Admiral, who won the Triple Crown in 1937, and Battleship, who triumphed in the prestigious English Grand National steeplechase.

Man o’ War’s impact can be seen in numerous successful racehorses through his descendants. Some notable examples include:

  • War Admiral – A son of Man o’ War, War Admiral won the prestigious Triple Crown in 1937 and became a successful sire himself, producing champions like Busher and Blue Peter.
  • Battleship – Another son of Man o’ War, Battleship found success in the world of steeplechase racing, winning the esteemed English Grand National in 1938.
  • Hard Tack – A son of Man o’ War, Hard Tack sired Seabiscuit, the legendary racehorse known for his incredible come-from-behind victories and inspiring story of resilience.
  • Clyde Van Dusen – A grandson of Man o’ War through his sire, Man o’ War’s son Reigh Count. Clyde Van Dusen went on to win the Kentucky Derby in 1929.
  • Pensive – A great-grandson of Man o’ War through his sire, Hyperion, who was a grandson of Man o’ War. Pensive won the Kentucky Derby and Preakness Stakes in 1944.


Nearco, an Italian-bred stallion, is another important sire from this era. His bloodlines can be traced through numerous modern racing champions, solidifying his position as a foundation sire in Thoroughbred history.

Nearco’s legacy can be seen in many successful racehorses through his descendants. Some notable examples include:

  • Nasrullah – A son of Nearco, Nasrullah sired Bold Ruler, who in turn sired the legendary Secretariat. Nasrullah’s other successful progeny include Red God and Grey Sovereign.
  • Royal Charger – Another son of Nearco, Royal Charger, went on to sire the influential stallion Turn-to, who in turn sired the great Hail to Reason.
  • Noor – A son of Nearco, Noor was a successful racehorse, defeating the legendary Citation four times. He went on to sire the outstanding racehorse and sire, Preceptress.
  • Northern Dancer – A grandson of Nearco through his sire, Nearctic. Northern Dancer became one of the most influential sires of all time, with his progeny including Nijinsky, Sadler’s Wells, and Galileo.
  • Kalamoun – A great-grandson of Nearco through his sire, Zeddaan. Kalamoun sired the successful racehorse and sire Kenmare, who went on to produce the influential sire Kendor.

These early 20th-century sires and their successful offspring have left a lasting legacy in the racing world. Their bloodlines continue to influence today’s champions, and understanding their impact on modern pedigrees is essential for anyone interested in racehorse breeding.

As the quest for the next great sire in Thoroughbred racing continues, the contributions of these trailblazing stallions and their progeny will always be remembered and celebrated.

Modern influential sires and their impact on the racing world

In today’s racing world, numerous influential sires continue to shape the bloodlines of successful racehorses, including prominent names like Galileo, Tapit, and Dubawi. Nevertheless, Northern Dancer stands out as exceptional.

Northern Dancer, a Canadian-bred racehorse, is considered one of the greatest sires of all time. Born in 1961, he had an impressive racing career, winning important races like the Kentucky Derby and the Preakness Stakes. After retiring from racing, Northern Dancer became a highly successful stallion, passing on his incredible genes to his offspring.

Many of his children and grandchildren went on to achieve great success on the racetrack, making Northern Dancer’s bloodline highly sought after by breeders. His influence can still be seen in the pedigrees of top racehorses today, proving the lasting impact of his exceptional bloodline on the world of Thoroughbred racing.

Analyzing and Evaluating Pedigrees

Analyzing pedigrees can help us make better decisions about breeding and racing horses, and it’s an enjoyable way to learn more about the world of Thoroughbred racing. Investigating a horse’s lineage offers valuable insights into their potential for success on the racetrack.

This knowledge assists breeders and trainers in matching horses with the characteristics that will most likely produce successful racehorses, considering their speed at various distances or surfaces. Moreover, understanding a horse’s pedigree is essential when choosing the ideal breeding partners, ensuring the optimal inheritance of desirable traits for future generations.

Here is a YouTube video that provides some helpful information about breeding horses and bloodlines.

YouTube video

Pedigree analysis techniques and tools

There are different techniques and tools that can help us analyze pedigrees more effectively. These methods will make it easier to understand a horse’s lineage so that owners and breeders make better decisions.

Some common methods include:

  1. Dosage profile and index: A mathematical system that assigns points to a horse’s ancestors based on their racing achievements, helping to predict a horse’s potential for success in specific race distances.
  2. Nicking: A practice that involves analyzing the compatibility between a sire and a dam, considering their respective bloodlines, to produce successful offspring.
  3. Online pedigree databases and software: These tools can help you research and visualize a horse’s lineage, making it easier to identify patterns and trends in their ancestry.

How to read a pedigree chart and interpret the information

A pedigree chart provides a visual representation of a horse’s ancestry, typically displaying four generations. Here’s how to read and interpret the information on a pedigree chart:

  1. The horse’s name is listed at the top, followed by its sire (father) and dam (mother) immediately below.
  2. The next level displays the grandparents (grandsires and grand dams), followed by the great-grandparents in the subsequent row.
  3. As you move down the chart, each generation doubles in size, with the number of ancestors increasing exponentially.
  4. Pay attention to the names of the ancestors, as certain horses may appear multiple times in a pedigree, indicating inbreeding.
  5. Look for black type, which is used to indicate stakes winners. Bold or highlighted names represent horses that have won or placed in significant races, making it easier to assess the quality of a horse’s lineage.

By learning to read and interpret pedigree charts, you can gain valuable insights into a horse’s lineage and potential, helping you make more informed decisions in breeding and racing.

Breeding Strategies for Success

One of the key aspects I’ve learned in my journey through racehorse breeding is the importance of selecting the right sire and dam to produce offspring with desired traits. This involves considering factors such as conformation, racing ability, temperament, and genetic compatibility.

By carefully evaluating the strengths and weaknesses of potential breeding partners, breeders can increase the likelihood of producing offspring with the ideal combination of characteristics for success on the racetrack.

The Role of Nicking and its Impact on breeding outcomes

Nicking is a strategy I mentioned earlier, which involves analyzing the compatibility between a sire and a dam based on their respective bloodlines. The goal of nicking is to identify patterns in the pedigrees of successful racehorses and use that information to select breeding partners that are likely to produce successful offspring.

In the past, nicking was an occupation in demand, with experts meticulously analyzing bloodlines before the advent of computers. Nowadays, you can subscribe to online nicking programs that help determine the best horses to pair. These programs use advanced algorithms to analyze pedigrees and suggest compatible mating partners.

However, there are still some experienced breeders and analysts who prefer the human touch when it comes to nicking. These “old-timers” rely on their years of expertise and intuition to assess bloodlines and identify the most promising pairings.

Both modern tools and human experts can help breeders make more informed decisions when choosing a mating pair, ultimately improving the chances of producing high-performing racehorses.

Nicking Examples

Secretariat, one of the most famous racehorses in history, was a descendant of Nearco. His sire, Bold Ruler, was a great-grandson of Nearco through the line of Nearco’s son, Nasrullah. Additionally, Secretariat’s dam, Somethingroyal, was a granddaughter of Man o’ War.

Seabiscuit, another legendary racehorse, was a descendant of Man o’ War. His sire, Hard Tack, was a son of Man o’ War. Seabiscuit’s dam, Swing On, was also a great-granddaughter of Man o’ War.

Dr. Fager, a champion racehorse and prolific sire, was also related to these influential sires. His sire, Rough’n Tumble, was a great-grandson of Man o’ War, while his dam, Aspidistra, was a great-granddaughter of Nearco.

Picture of a racehorse selling at auction for 7,000,000.  This demonstrates the importance of racehorse pedigrees.

The Role of Pedigree in the Sales and Auctions Market

In my experience with the sales and auction markets, I’ve observed that a racehorse’s pedigree has a significant impact on its value. Buyers and sellers alike recognize that a strong pedigree often translates to a higher likelihood of success on the racetrack.

Horses with proven bloodlines, especially those related to successful sires, dams, and other racing champions, tend to command much higher prices because they are considered to possess the desired traits for racing excellence.

Trends in racehorse auctions and the importance of bloodlines

Throughout the years, the importance of bloodlines has remained a constant factor in the racehorse auction markets. Buyers often pay close attention to the pedigrees of horses on offer, looking for strong bloodlines and notable ancestors that could indicate a higher probability of racing success.

As a result, horses with impressive pedigrees, especially those from highly sought-after sires or dams, often fetch premium prices at auction. For example, Northern Dancer, a highly influential sire, started his stud career with a fee of $10,000.

After a few successful breeding seasons, his stud fee soared to $500,000 due to the exceptional performance of his progeny. Keeping an eye on trends in the racing world and identifying up-and-coming bloodlines can be an essential part of staying ahead in the sales and auction markets.

For both buyers and sellers in the racehorse market, understanding and evaluating pedigrees is crucial for making informed decisions. Here are some tips to help navigate the sales and auctions market based on pedigree:

  1. Research the pedigrees of horses on offer: Familiarize yourself with the bloodlines, racing achievements, and breeding records of the ancestors in a horse’s pedigree.
  2. Assess the compatibility of bloodlines: When considering a purchase for breeding purposes, evaluate the compatibility of the horse’s bloodlines with your existing stock or desired traits.
  3. Consider the market trends: Keep up-to-date with the latest trends in the racing world, including emerging bloodlines and the performance of offspring from specific sires or dams.
  4. Be cautious with inbreeding: While some inbreeding can be beneficial, be mindful of the potential risks associated with excessive inbreeding, such as genetic disorders and reduced genetic diversity.
  5. Consult with experts: If you are unsure about a horse’s pedigree or need advice on making a purchase, consider seeking the guidance of pedigree consultants or experienced breeders.
Picture of a horse at a breeding farm.

Success Stories from Renowned Racehorse Breeding Farms

While there are many stories of failed racehorse breeding farms, some that stay the course achieve remarkable success. In this section, we’ll spotlight two of the best in the world.

These outstanding establishments have made their mark in the Thoroughbred racing world, consistently producing top-quality racehorses through their expert breeding practices and unwavering dedication to excellence. Let’s delve into the accomplishments of these prestigious breeding farms and the exceptional horses they’ve brought into the racing world.

Calumet Farm

Located in Lexington, Kentucky, Calumet Farm is one of the most storied and successful horse breeding farms in American Thoroughbred racing history. The farm has bred and raised numerous champions, including Triple Crown winners Whirlaway and Citation. Calumet Farm’s yearlings have consistently fetched high prices at prestigious auctions.

For instance, at the 2017 Fasig-Tipton Saratoga Select Yearling Sale, Calumet Farm sold a yearling colt sired by Curlin out of their mare Franscat for an impressive $1.5 million. This sale highlights the high demand and value attributed to yearlings with strong pedigrees from esteemed breeding farms like Calumet Farm.

Coolmore Stud

Another prominent breeding operation is Coolmore Stud, with locations in Ireland, the United States, and Australia. Coolmore has been consistently successful in producing high-quality racehorses, and their stallions include some of the most influential sires in the industry, such as Galileo and the late Sadler’s Wells.

One example of their success can be seen in the 2018 Tattersalls October Yearling Sale, where a yearling colt by Galileo, out of the mare Shastye, sold for a staggering £3.4 million (approximately $4.4 million).

Both Calumet Farm and Coolmore Stud serve as prime examples of how investing in quality bloodlines and breeding practices can lead to outstanding success in the competitive world of Thoroughbred racing. Their achievements underscore the importance of understanding racehorse pedigrees and the role they play in shaping the future champions of the sport.


Understanding racehorse pedigree and bloodlines is an essential aspect of the horse racing and breeding world. From the basic concepts and terminology to the importance of bloodlines in racing performance, it’s clear that a horse’s lineage plays a significant role in determining its potential for success.

By learning to analyze and evaluate pedigrees, breeders and enthusiasts can make more informed decisions when it comes to breeding strategies and navigating the sales and auction market.