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How are Racehorses, Bred? Tradition vs. Modern Science

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This time of year always brings me joy as I watch the playful foals—future racehorses—frolic in the pastures. However, I hadn’t given much thought to the intricate process that leads to their arrival. Intrigued, I delved into research to gain a better understanding of how racehorses are bred.

For an offspring to be registered as a Thoroughbred racehorse, the sire and dam must engage in “live cover” mating, as artificial insemination is not allowed in this breed. In contrast, Quarter Horse broodmares can be bred either through live cover or artificial insemination, providing more flexibility in the breeding process.

Racehorse breeding merges time-honored traditions with modern science, combining age-old practices and cutting-edge research. This blog post delves into the captivating interplay between tradition and science, revealing how they collaborate to produce future champions.


Thoroughbred studs must “live cover” a mare.

In the Thoroughbred breeding industry, the practice of “live cover” is a strict requirement. This means that a Thoroughbred stallion must physically mate with a mare in order for their offspring to be eligible for registration as a Thoroughbred racehorse.

The rule is enforced to maintain the integrity of the breed’s lineage and ensure accurate record-keeping of pedigrees. Unlike some other breeds, artificial insemination is not allowed for Thoroughbreds, making the live cover method an essential aspect of the breeding process.

The live cover process begins with an examination of the broodmare. The veterinarian will keep a close eye on the mare, watching for signs of ovulation. He may run a test to determine which day and time will make conception the most likely.

Once the mare has entered ovulation, she is brought to a select location for breeding by an experienced handler. Safety is paramount for all involved. After she settles into her new place, her tail is wrapped, and she is thoroughly cleaned. Next, a teaser stallion will be brought in to get her ready for breeding.

The stallion is brought to the breeding location and cleaned as well. If everything is right and all parties ready, the stud is walked up behind the mare and mounts her. This process will only take a few minutes. Afterward, both are cleaned and brought back to their respective areas.

How artificial insemination could harm Thoroughbred horseracing.

Artificial insemination (AI), while offering some advantages, could potentially have negative impacts on the horseracing industry if it were to be adopted. Here are some potential drawbacks:

  1. Diminished genetic quality: With AI making it easier and less expensive to access top stallions, there is a risk that the gene pool may become too concentrated around a small number of popular sires. This could lead to reduced genetic diversity and increase the likelihood of hereditary health issues or detrimental traits emerging in the racing population.
  2. Oversaturation of the market: As AI can result in more foals from popular stallions, the market may become oversaturated with horses carrying the same bloodlines. This could lead to diminishing returns for breeders and a decreased demand for breeding services.
  3. Loss of tradition: The Thoroughbred racing industry has a long-standing tradition of live cover breeding. Adopting AI could be seen as a departure from this tradition, potentially alienating some stakeholders within the racing community.
  4. Ethical concerns: The use of AI could potentially result in overbreeding or breeding practices that prioritize commercial interests over the welfare of the horses involved. This might raise ethical concerns among industry participants and animal welfare advocates.
  5. Regulatory challenges: Introducing AI into the Thoroughbred racing industry would require reevaluating current breeding rules and regulations. This could lead to significant debate and disagreement among stakeholders, potentially causing divisions within the racing community.

It is crucial to weigh the potential advantages and disadvantages of AI carefully and consider the overall impact on the industry before implementing any changes to established breeding practices.

Why artificial insemination is good for horse racing.

While artificial insemination (AI) is not currently allowed in Thoroughbred horse racing, there are several potential benefits if the industry were to consider adopting this breeding method:

  1. Genetic diversity: AI allows breeders to access a wider pool of stallions, even those located in distant countries, without the need to transport mares long distances. This facilitates the introduction of new bloodlines and promotes genetic diversity in the racing population.
  2. Disease control: AI reduces the risk of transmitting sexually transmitted infections or contagious diseases between horses during the breeding process. Semen can be tested and treated, if necessary, before insemination, leading to healthier breeding stock.
  3. Improved conception rates: AI allows for better control of the timing and process of insemination, potentially resulting in higher conception rates. This can lead to more successful pregnancies and increased efficiency in the breeding process.
  4. Reduced injury risk: Mating accidents and injuries can occur during live cover, whereas AI eliminates the need for direct physical contact between the mare and stallion. This reduces the risk of injury to both horses and handlers.
  5. Conservation of genetic material: AI enables the collection and preservation of semen from valuable stallions, ensuring their genetic material can be used even after their death or retirement from breeding. This can help to preserve exceptional bloodlines for future generations.

However, it is important to note that the Thoroughbred industry has long-standing traditions and regulations in place. Any changes to breeding practices would require careful consideration and consensus within the racing community.

Racing Quarter horse mares can be artificially inseminated.

The American Quarter Horses Association does not have a “live cover” requirement for the registration of quarterhorses. Artificial insemination is an acceptable method of breeding. .

Artificial Insemination: The first thing we have to do is collect the semen from the stallion. This process begins with cleaning the stud thoroughly to keep the process sanitary.

Next, a mare in heat will be introduced to the horse to excite him. After he is sufficiently excited, the mare will be walked near a dummy mount fitted with an artificial vagina and an attached sterile collection bag. The stallion will mount the dummy and ejaculate into the artificial vagina, and the semen is collected.

Now that we have successfully collected the semen, it can be introduced into a mare. The typical procedure is to wrap the mare’s tail and hold it out of the way. Next, the vagina and the surrounding area are cleaned.

The veterinarian then inserts a tube inside the mare, which extends into the uterus. Once the tube is confirmed to be in place, the semen is injected from a syringe into the tube. Afterward, the mare is observed to ensure she is ovulating. If not, medicine will be used to induce ovulation.

You may elect to confirm pregnancy with a mobile ultrasound scanner. (You can check out the products review page for information about mobile ultrasound devices)

Racehorse breeding is a risky business.

Racehorse breeding is undoubtedly a risky business, with various challenges and uncertainties that breeders must navigate in their quest to produce top-quality racehorses. Some factors that contribute to the riskiness of the industry include:

  1. Genetic unpredictability: While a careful selection of pedigree and bloodlines can increase the chances of breeding a successful racehorse, there is always an element of unpredictability in the genetic lottery. Even the offspring of champion racehorses may not possess the same level of talent or athleticism.
  2. Health complications: Horses can experience health issues during the breeding process or pregnancy, and newborn foals are susceptible to various health problems. Ensuring the well-being of the horses involved and managing potential complications requires expertise, diligence, and financial resources.
  3. Market fluctuations: The racehorse market is influenced by economic conditions, trends, and the overall demand for specific breeds or bloodlines. Breeders must be prepared to adapt to market changes and adjust their breeding strategies accordingly.
  4. High costs: Horse breeding can involve substantial upfront costs, including purchasing quality broodmares and stallions, stud fees, and ongoing expenses related to the care and management of the horses. These costs can be challenging to recoup, particularly if the offspring do not perform as expected.
  5. Competition: The horse breeding industry is highly competitive, with numerous breeders striving to produce the next champion racehorse. Standing out in this crowded market requires not only exceptional horses but also effective marketing and networking.

Despite the risks, racehorse breeding can be an immensely rewarding venture for those who are passionate about the industry and committed to navigating its challenges.

It’s estimated that only 6% of racehorses earn enough money to cover their expenses, and just a small fraction of these go on to win any significant money. Owners and breeders try to increase their chances of success with superior breeding.

Choosing the right stud is critical.

The first step in the breeding process is determining what stud you want to breed with your broodmare. This is the most important step in the process and also the hardest.

There is no surefire method to determine which stud is best to breed for your mare. However, there are bloodlines that do match better than others. Also, certain studs are generally more successful than others, regardless of the number of races they’ve won in their career.

Racehorse breeding is a high-risk gamble.

Picture of a racehorse training in the morning.
Morning workout

Racehorse breeding is a genetic lottery. All the numbers are in the pool. You just have to be lucky enough to match them correctly to have a winner. What methods are used by the breeder to increase their chances of producing a winner?

Horse owners dream of owning the next Kentucky Derby or All-American futurity winner. Yes, the purse money is excellent, but the real windfall comes from stud fees. For example, American Pharoah won the first Triple Crown in 37 years in 2015. His stud fees started at $200,000 per cover, and he could cover over 100 mares per year. (Click here to read an article about why some racehorses are gelded)

Genetics is critical in racehorse breeding.

Understanding the role of genetics in horseracing can be illustrated by examining the bloodlines of successful racehorses. While not every Kentucky Derby winner goes on to sire other Derby winners, strong bloodlines play a significant role in producing top-performing offspring.

For example, the renowned stallion Northern Dancer, who won the 1964 Kentucky Derby and Preakness Stakes, became one of the most influential sires of the 20th century. Breeding a successful racehorse is a complex endeavor, requiring a combination of good conformation, durability, and speed to excel in racing.

Selecting the horses to breed is challenging.

Choosing the right horses to breed in a racehorse breeding business can be a challenging and complex decision-making process. Successful breeding programs rely on carefully selecting horses based on several factors, including:

  1. Pedigree: The bloodlines of the horses play a crucial role in determining the potential quality of their offspring. Researching the ancestry and performance of both the sire and dam can provide valuable insights into the likelihood of producing offspring with desirable traits and abilities.
  2. Conformation: Physical traits and structure are essential when selecting horses for breeding. Horses with good conformation are more likely to produce offspring that can excel in their chosen discipline, whether racing, dressage, or showjumping.
  3. Performance and Progeny: Analyzing the performance records of potential breeding horses, as well as the performance of their offspring, can help identify which horses have a proven track record of success. This information can be an important indicator of future breeding success.
  4. Temperament: The temperament of breeding horses is important, as their offspring can inherit it. Horses with a calm, trainable disposition are more likely to produce offspring that are easier to manage and train.
  5. Market demand: Assessing market demand for specific breeds, disciplines, or bloodlines can help guide your breeding decisions. By identifying trends and preferences within your target market, you can focus on breeding horses that will be in high demand and command a premium price.
  6. Genetic health: Ensuring that the horses you choose to breed are free from genetic disorders or hereditary health issues is crucial for producing healthy and viable offspring. Genetic testing and thorough veterinary examinations can help identify and prevent the propagation of such conditions.

By considering these factors and conducting thorough research, horse breeders can make informed decisions and improve their chances of creating successful breeding programs that yield high-quality horses.

Picture of a Thoroughbred mare and her offspring.

Through the years, humans have developed different theories on how to produce the ultimate horse. The following are some of these methods.

Telegonic is an ancient theory that has not proven effective.

Telegonic theory has been around since the days of Aristotle, and the basic premise is that previous pregnancies influence future offspring. The theory goes that when a stud covers a mare, his genes remain with the horse and will influence the next offspring.

As a mare has more foals, she will have a higher chance of producing offspring with the best genes from all her previous mating partners. Current understanding of genetics and inheritance shows that offspring traits are determined solely by the genes of their biological parents, with no influence from previous mates.

Linebreeding is the most popular breeding method.

Linebreeding is the presence of an ancestor twice or more in a horse’s pedigree, with at least one strain present from each parent. There are many reasons this is desirable.

Breeders have determined that if the horses who appeared in the pedigree more than once were present through a different son or daughter, it improved the horse. This leads to a reduction in genetic variance and an increase in the desired traits.

A stallion passes his Y-chromosome to his sons and his X-chromosomes to his daughters. This could explain why line breeding on a horse via a son and a daughter is exceptionally successful. Linebreeding is the most popular form of reproduction in thoroughbreds.

Pattern breeding is line breeding with a twist.

Pattern Breeding is a variation of linebreeding, wherein you try to repeat a pattern of ancestors found in the broodmare with a similar family found in the stallion’s pedigree.

Two or three influential ancestors in the same section of lineage increase the chances of passing the desirable characteristics to the offspring. Pattern breeding is still a viable method used by breeders today.

Inbreeding is no longer a preferred breeding method.

Inbreeding is the duplication of ancestors within the first four generations. Although there has been some success with inbreeding horses over the years, it is no longer a favored breeding method.

We know the stories of hemophilia amongst the royal bloodlines of Europe. Similar issues can arise with the inbreeding of horses.

Outcrossing/outbreeding increases genetic diversity.

Outcrossing or outbreeding is the breeding of unrelated horses. This is done to increase genetic diversity in the bloodline reducing the probability of genetic abnormalities. We know line-breeding can lead to the production of a successful racehorse; however, too much inbreeding can lead to physical problems.

Studies have shown that mares with too much of the same genetic makeup will benefit from the introduction of new blood. Outcrossing provides for the introduction of new DNA by breeding with a stud completely outside her family tree. Today it is tough to find pedigrees without some cross when you look back six generations.

To “Nick” a horse means to link successful bloodlines.

To determine which bloodlines cross best with a broodmare is referred to as a Nick. Nick is the term used to describe a proven successful link between two lines of stallions.


A good example is Northern Dancer/Star Kingdom pedigrees. Broodmares from the Star Kingdom line has proven to produce successful offspring from Nothern Dancer stallions. There are many other successful combinations.

Nicks have led to the positive development of the thoroughbred horse. For years professional nickers made an excellent living advising owners on the best. Nick for their horses. However, with the advent of the internet and DNA studies, Nickers is not as prevalent.

Appendix Bred can be registered as a Quarter horse.

An appendix-bred horse is a cross between a registered quarter horse and a registered thoroughbred. The appendix reference may continue down the pedigree based on certain conditions. Appendix bred horse is desired for displaying the best traits of both breeds, the calmer disposition of a quarter horse, and the thoroughbred’s athletic ability.

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