The Thoroughbred is a popular horse breed widely recognized for its speed and athleticism. Bred specifically for horse racing since the 17th century, Thoroughbreds continue to rule racetracks around the world.

While the racing industry produces tens of thousands of Thoroughbreds each year, most of these horses move on to second careers after they retire from the track at young ages.

Fortunately, many of the characteristics that make this breed ideal for racing also translate to success in various equestrian sports. However, off-track Thoroughbreds (OTTBs) often have unique training, health, and nutrition needs.

This article will discuss the history, breed characteristics, common health problems, and nutrition requirements of Thoroughbred horses. Keep reading to learn more about caring for and feeding your Thoroughbred.

Thoroughbred History

While horse racing dates back to ancient times, the history of the Thoroughbred breed began just over 300 years ago with three foundation stallions. Since then, selective breeding for speed and endurance has continued to improve the Thoroughbred we know today.


The modern Thoroughbred can trace its ancestry to three stallions imported to England from the Middle East in the late 1600s and early 1700s. These foundation stallions included the Godolphin Arabian, the Darley Arabian, and the Byerley Turk. [1]

Breeders crossed these stallions with English mares to produce offspring that could maintain high speeds over long distances. The term “thro-bred” first emerged in 1713 to describe the resulting cross. [1]

Genetic studies show that most Thoroughbreds alive today descend from just 27 stallions from the 18th and 19th centuries. Over 95% of paternal lineages trace back to the stallion Eclipse, a great-great-grandson of the Darley Arabian. [2]

The first breed registry for Thoroughbred horses emerged with the original volume of the General Stud Book, published by James Weatherby in 1791. The studbook collected and documented the pedigrees of racehorses descended from these bloodlines in Great Britain.

Historic Use

Records indicate flat racing existed in England as early as the year 1174, but the first formal publication devoted to racing, the Racing Calendar, wasn’t founded until 1727. The launch of this publication corresponds with the rising popularity of Thoroughbred bloodlines at racetracks. [3]

The sport gained royal support in Britain under the reign of Charles II, an avid horse racing enthusiast, in the 17th century. [4]

In the early 18th century, Thoroughbred racing concentrated on longer races of up to 4 miles and multiple heats. Race distances changed by the end of the century with the establishment of the English classic races, ranging from 1 mile to 1.75 miles. [1]

The change in race distance led to a shift in breeding practices, emphasizing horses with greater speed that could race at younger ages. Thoroughbred bloodlines in England during this time were also developed for steeplechasing. [1]

American settlers soon brought the sport to the colonies. Bulle Rock, the first Thoroughbred in the American Colonies, crossed the Atlantic in 1730. In the early 19th century, match races popularized Thoroughbred racing in the United States. [5]

In addition to their role in the racing industry, Thoroughbreds were also used to improve other breeds in the U.S. The imported stallion Messenger served as the foundation sire of the Standardbred, and Thoroughbred blood was critical for the development of the American Quarter Horse.

Breed Registry

The Jockey Club is the North American breed registry for Thoroughbred horses. This registry maintains the American Stud Book, which records every Thoroughbred imported to or born in the United States, Canada, and Puerto Rico.

First published in 1873, the American Stud Book is the North American version of Britain’s General Stud Book. The Jockey Club was incorporated in 1894 to establish a governing body dedicated to improving Thoroughbred breeding and racing in North America.

Today, the club’s database contains pedigree information of more than 1.8 million horses dating back to the late 1800s. That number continues to grow, with approximately 20,000 Thoroughbreds added each year. [6]

Unlike many breed registries, The Jockey Club only registers foals resulting from live cover of the mare by the stallion. Thoroughbreds also have a closed studbook. Both the sire and dam must be registered in the American Stud Book for a foal to be eligible for registration. [7]

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Breed Characteristics

The breed standard for the Thoroughbred is primarily based on racing ability. Instead of being selected for specific conformational traits, horses demonstrate their breeding value through their track performance.

Selective breeding has resulted in conformation and temperament characteristics often associated with soundness, speed, and endurance. These characteristics can also contribute to success in different arenas after the horse’s racing career.


Many aspects of the Thoroughbred’s appearance reflect their Arabian blood. An attractive Thoroughbred has a refined head with widely spaced eyes. Like Arabians, Thoroughbreds are considered hot-blooded horses.

Most Thoroughbreds range in height from 15.2 to 17 hands. In addition, these horses usually have lean bodies suitable for speed. Therefore, the average 16-hand Thoroughbred will weigh significantly less than a 16-hand horse from a stockier breed.

Most Thoroughbreds have slightly longer and lighter necks than other breeds. Ideal conformation includes high and well-defined withers that lead to a short, evenly curved back. A deep chest and sloped, well-muscled shoulder aid running ability. [8]

The heart girth of a Thoroughbred is usually deep and relatively narrow. Long legs with clean, pronounced tendons promote soundness and stride length. The upper hind leg should have long, strong muscling with a long thigh bone and wide hip angle for power. [9]


Thoroughbreds come in a variety of solid coat colours. The following colours are recognized by The Jockey Club: [7]

  • Bay
  • Black
  • Chestnut
  • Brown
  • Roan
  • Gray
  • Palomino
  • White


Horses bred for speed and performance often have spirited, high-energy personalities. Thoroughbreds are generally intelligent and sensitive and may not make the best mounts for beginner riders.

However, every horse is an individual. Thoroughbreds with personalities ill-suited for the race track often find a better fit in a second career. Many experienced competitors value the spirited temperament of the Thoroughbred in a high-performance partner.


Modern horse racing primarily focuses on young horses, so most Thoroughbreds only spend a few years at the track. While some talented stallions and mares start breeding after successful racing careers, most Thoroughbreds move on to riding homes.

The Jockey Club supports second careers for retired racehorses through the Thoroughbred Incentive Program (TIP). With support from TIP and other organizations that support retraining these horses, many Thoroughbreds have found success off the racetrack.

Thoroughbreds are commonly retrained for English disciplines after their racing careers. In the past century, several Thoroughbreds have risen to the top of the Olympic disciplines of Dressage, Show Jumping, and Eventing.

While warmbloods heavily dominate modern dressage and show jumping today, Thoroughbred stars still excel at the top level of eventing. These include Blackfoot Mystery, an OTTB ridden by Boyd Martin at the 2016 Olympics in Rio de Janeiro.

Many thoroughbreds owners enjoy their horses as versatile pleasure mounts. This athletic breed is just as at home in a fox hunting field or hunter/jumper arena as a race track or cross country course.

Thoroughbred Breed Health

The closed studbook of Thoroughbreds can contribute to health problems exacerbated by inbreeding. Some research suggests that selective breeding for speed may have increased the risk of cardiac and skeletal issues in thoroughbreds. [10]

There are several ways that a racing career can impact horse health beyond the increased risk of musculoskeletal injury. Retired racehorses often come to their new owners with health challenges and require unique management to thrive in their second careers.

Retired Racehorses

Data from 27 trainers over 13 months revealed that involuntary causes accounted for nearly half of all racehorse retirements. The most common reasons included musculoskeletal injuries, respiratory problems, cardiac conditions, and behavioural problems. [11]

Racehorses are also subject to increased stress, and multiple studies have shown that nearly every Thoroughbred racehorse has some degree of gastric ulceration. New owners of OTTBs should work with their veterinarians to diagnose pre-existing conditions. [12]

Health Problems

Thoroughbreds start training at a very young age. These young horses can be susceptible to microdamage of the subchondral bone if training schedules do not provide enough recovery time for the bone to adapt to increased loading forces. [13]

As a result of chronic fatigue, damage to the distal metacarpal subchondral bone can accumulate over a racing career and increase the risk of bone injury. Proper nutrition and a strategic exercise program can help maintain bone strength.

Racehorses also have a high incidence of exercise-induced pulmonary hemorrhage. Thoroughbreds that struggle with this condition during their racing careers have a higher risk of EIPH recurrence if they engage in intense exercise. [14]

Some Thoroughbreds have abnormally large hearts. This anatomy increases cardiac output during a race, and is associated with superior performance. [15] It has been dubbed the “X Factor”.

Thoroughbreds also have a reputation for bad feet. Weak hooves in Thoroughbreds likely arise from genetic and environmental factors. Proper nutrition and high-quality farrier care are vital for supporting hoof growth and soundness.

Care and Management

If you’re bringing home an OTTB, remember that his new life likely varies significantly from his life at the track. Try to make transitions gradually to limit stress.

This breed is usually highly energetic and does best with regular exercise and turnout. Some owners struggle with behavioural problems if their Thoroughbreds don’t have a safe outlet for excess energy.

If possible, keep your Thoroughbred turned out on pasture to meet his needs for forage and freedom of movement. Unlike some breeds, Thoroughbreds have a low risk of metabolic conditions associated with grazing. [16]

Regardless of your housing situation, minimize exposure to mud and dirty bedding. Excess environmental moisture can compromise hoof wall integrity if your Thoroughbred struggles with hoof problems. [17]

OTTBs usually need significant retraining before they’re ready to start their new careers. Seek guidance from qualified trainers if you don’t have experience working with off-track Thoroughbreds.

Some behavioural problems can indicate an underlying digestive issue. Consult your veterinarian if you suspect your Thoroughbred has a health problem, and work with a nutritionist to evaluate his diet.

Thoroughbred Nutrition

Nutrition plays a significant role in successfully transitioning Thoroughbreds from the racetrack and keeping them healthy throughout their second careers. When a Thoroughbred leaves the racetrack, his exercise intensity level and nutritional needs change significantly.

Racehorses are commonly fed high-grain diets to meet the energy demands of racing. Many TB owners continue feeding large grain rations, assuming this is the only way to maintain weight on this hot-blooded breed.

However, this diet can contribute to digestive issues, including a higher risk of colic and gastric ulcers. Gut dysfunction can prevent Thoroughbreds from absorbing the nutrients they need from their diet to maintain their body condition. [18]

Weight Maintenance

Thoroughbreds are generally considered hard keepers. This breed has more difficulty maintaining weight than easy keeper breeds, such as Quarter Horses.

However, owners shouldn’t overlook weight loss as a sign of poor gut health. Many Thoroughbreds have faster metabolisms than other horses, but if your TB struggles to maintain weight on a balanced diet, you should contact your veterinarian to investigate for underlying health issues.

While Thoroughbreds are naturally lean, they should maintain a body condition score of at least 4 out of 9. Determining your horse’s body condition score and healthy body weight can help you optimize his diet.

If your horse cannot maintain an adequate body condition score on free choice forage alone, consider adding a 1:1 mixture by dry weight (not volume), of soaked beet pulp and wheat bran. This provides balanced macrominerals and has much lower starch than grains while providing equivalent calories.

Diet for a Mature Thoroughbred in Light Work with Normal Body Condition


Feed Maintenance Diet
(Amount / Day)
High-Quality hay (>12% crude protein) free-choice
Salt 30 g (2 tbsps)
Omneity® Pellets 200 g (2 scoops)
Diet Analysis
Digestible Energy (% of Req) 109%
Protein (% of Req) 192%
NSC (% Diet) 8.9%


Forage should be the primary source of nutrients in the diet of all horses, including Thoroughbreds. Selecting high-quality, high-calorie hay can help meet your horse’s energy needs with a forage-based diet. Look for soft, leafy, immature, green hay to maximize palatability and intake.

You can learn more about identifying forage and estimating its maturity in this article. Fresh pasture is also an excellent forage source for horses with higher calorie needs.

Also, ensure your thoroughbred receives a balanced diet with adequate amounts of amino acids, vitamins, and minerals. Deficiencies in these nutrients can lead to hoof problems, poor coat quality, impaired immune function, poor performance and more.

In the sample diet, Mad Barn’s Omneity® is added to provides these key micronutrients commonly deficient in forage.

Feeding Omneity® will ensure your Thoroughbred has all of the nutrients he needs to grow strong hooves , maintain a shiny coat and support performance. Available in a powdered or pelleted form, Omneity® is an all-in-one solution for optimal well-being.

Omneity – Premix

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Thoroughbreds need adequate dietary protein to support topline and muscle mass. Alfalfa hay can be an excellent source of protein for Thoroughbreds, particularly if your grass hay is low in protein. Alfalfa has a reputation for making some horses more excitable, possibly because the two most abundant amino acids, L-glutamate and L-aspartate, are excitatory neurotransmitters in the brain. [21]

The high calcium content in alfalfa also helps buffer stomach acid in Thoroughbreds with a history of gastric problems. However, alfalfa should not be your horse’s primary forage, as large amounts can throw off your horse’s calcium and phosphorus ratio. [19]


While some Thoroughbreds can thrive on a forage-only diet, others may benefit from the appropriate inclusion of concentrates to increase energy supply. For example, Thoroughbreds in heavy work may need additional energy from concentrates to support work demands.

If you choose to feed a concentrate, split your horse’s ration into multiple small meals throughout the day to minimize the risk of gastrointestinal upset. Work with an equine nutritionist to determine if your Thoroughbred needs grain and select a formula suitable for your horse.

Learn how to read feed tags so you can compare different commercial feeds and select the best one for your horse.

Even if you feed a complete feed or ration balancer, your Thoroughbred’s diet can still be deficient in some vitamins and trace minerals, depending on your feeding rate and your hay analysis. Most equine diets require supplementation to fill the nutritional gaps from forage.

Water & Salt

Like all horses, Thoroughbreds need constant access to fresh water and salt. Many horses won’t consume enough sodium from a salt lick alone, so feeding plain, loose salt and providing free-choice access to salt at all times is recommended.

Nutritional Supplements

Gut Health

Thoroughbreds on high-starch complete feeds can have gut issues that disrupt the microbiome and kill off fibre-fermenting bacteria. One study found that 25% of racehorses fed an average of 7.5 kg of grain daily had more acidic conditions in the hindgut. [18]

These horses need veterinary management and additional gut support to maintain optimal digestive function. Consider feeding a probiotic supplement with added yeast to promote feed efficiency, hindgut health and nutrient absorption.

Mad Barn’s Visceral+ provides probiotics, yeast, herbs, minerals, and amino acids to support the entire digestive tract.


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  • Our best-selling supplement
  • Maintain stomach & hindgut health
  • Supports the immune system
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Fat Supplements

Horses that need to gain condition benefit from dietary sources of healthy fats. Fat is a highly digestible and concentrated source of calories that does not contribute to excitability in Thoroughbreds. [20] Consider using a fat source rich in omega-3 fatty acids, such as flax oil.

Mad Barn’s W-3 Oil contains the omega-3 fatty acid DHA, which can also help to support joint health in OTTBs.

w-3 Oil

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  • Promotes joint comfort
  • Helps to fight inflammation
  • Skin & coat condition
  • Palatable source of Omega-3's

To further support joint health, particularly in growing horses supplementation with milk basic protein, a derivative of whey protein, has been shown to improve bone formation. [22]

Is Your Horse's Diet Missing Anything?

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  2. Cunningham, E. et al. Microsatellite diversity, pedigree relatedness and the contributions of founder lineages to thoroughbred horses. Anim Genetics. 2001.View Summary
  3. Kay, J. Still Going After All These Years: Text, Truth, and the Racing Calendar. Sport in History. 2009.
  4. Nash, R. The Sport of Kingmakers: Horse Racing in Late Stuart England. Int J of the History of Sport. 2020.
  5. Struna, N. The North-South Races: American Thoroughbred Racing in Transition,1823-1850. 1981.
  6. The Jockey Club. Annual North American Registered Foal Crop. Fact Book. 2022.
  7. The Jockey Club. The American Stud Book Principle Rules and Requirements. Registry. 2023.
  8. Mawdsley, A. et al. Linear assessment of the Thoroughbred horse: an approach to conformation evaluation. Equine Vet J. 1996. View Summary
  9. Anderson, T. et al. The role of conformation in musculoskeletal problems in the racing Thoroughbred. Equine Vet J. 2010. View Summary
  10. Welsh, C. et al. Estimates of genetic parameters of distal limb fracture and superficial digital flexor tendon injury in UK Thoroughbred racehorses. The Vet J. 2014. View Summary
  11. Crawford, K. et al. Appraising the Welfare of Thoroughbred Racehorses in Training in Queensland, Australia: The Incidence, Risk Factors and Outcomes for Horses after Retirement from Racing. Animals. 2021.View Summary
  12. Begg, L. et al. The prevalence and distribution of gastric ulceration in 345 racehorses. Austral Vet J. 2008. View Summary
  13. Whitton, R. et al. Subchondral bone microdamage accumulation in distal metacarpus of Thoroughbred racehorses. Equine Vet J. 2018. View Summary
  14. Morley, P. et al. Exercise-induced pulmonary haemorrhage impairs racing performance in Thoroughbred racehorses. Equine Vet J. 2014.View Summary
  15. Young, L. et al. Left ventricular size and systolic function in Thoroughbred racehorses and their relationships to race performance. Appl Physiol. 2005. View Summary
  16. Frank, N. Equine Metabolic Syndrome. Vet Clin Equine Pract. 2011.
  17. Moyer, W. Hoof wall defects: chronic hoof wall separations and hoof wall cracks. Vet Clin Equine Pract. 2003.
  18. Richards, N. et al. The effect of current grain feeding practices on hindgut starch fermentation and acidosis in the Australian racing Thoroughbred. Austral Vet J. 2006. View Summary
  19. Nadeau, J et al. Evaluation of diet as a cause of gastric ulcers in horses. Am J Vet Res. 2000. View Summary
  20. Redondo, A. et al. Fat diet reduces stress and intensity of startle reaction in horses. Appl Anim Behav Sci. 2009.
  21. Giner-Chavez, B.I. et al. Comparison of the Precipitation of Alfalfa Leaf Protein and Bovine Serum Albumin by Tannins in the Radial Diffusion Method. J Sci Food Agri. 1999.
  22. Inoue, Y. et al. The effect of milk basic protein supplementation on bone metabolism during training of young thoroughbred racehorses. Equine Vet J Suppl. 2006 . View Summary