Kentucky Derby: Physiologically Training the Racehorse

The Kentucky Derby is considered "The Greatest Two Minutes in Sport." This race is regarded as a Grade I stake horse race for thoroughbreds. These horses compete in this famous race at the age of three, and the horse who runs the 1 ¼ miles distance in the shortest time wins a great purse of $1.24 million. The average horse running the Kentucky Derby competes at an average of 37 miles per hour. While horses have carried humans and have been used for transportation of goods and work for many millennia, including all of the equine sports we see today, horse racing is the only activity occurring within a very narrowly defined set of circumstances. The weight and height of the rider are confined to a very narrow range prescribed by the racing commissions. The jockey usually weighs between 108 to 118 pounds. Jockeys are often no taller than 5' 6" to compress themselves into the most aerodynamic position on the horse's back as possible. Both of these requirements aid in the production of speed and lessen the muscular activity necessary to produce that speed. Racing is also carried out on footing that adheres to a particular set of requirements. The footing contributes to the horse's ability to deliver maximum speed, while hopefully protecting joints, tendons, and ligaments from injury.

Assuming that the horse is already a three-year-old and has already raced his two-year-old year and is in contention for a Kentucky Derby spot, race distances will have ranged from six furlongs to 1 1/16 miles. A training program needs to address speed, but also needs to address stamina. Training normally takes place daily between 6 am, and 10 am. The horse is warmed up with a jog once they hit the track. The duration of the jog is about 1/8 of a mile. The next ½ mile is exercised at a slow gallop. Then the horse breezed for the following ¼ mile, where the horse works at a moderate speed without being urged. Next, the horse slows to a slow gallop for a ¼ mile and finishes with a jog for a ¼-½ mile. One month before the Kentucky Derby, once a week, the breeze components of the workout are expanded for 3-6 furlongs, and the slow gallop components are compressed. A stopwatch is used to record the time of each breeze segment. These segments should become quicker throughout the training program. ("Breeders' Futurity at Keenland", 2019; Mendoza, 2014).

A heart monitor can be used during training sessions to record the heart rate before, during, and after the workout (Figure 1). A horse's maximum heart rate ranges between 220-250 beats per minute. The point of appropriate training is to avoid maximum heart rate and anaerobic metabolism as much and as long as possible. At maximum heart rate, pumping is inefficient, because the heart chambers do not have enough time between beats for maximum fill and ejection of oxygenated blood to the rest of the body. Appropriate training maximizes aerobic energetics by keeping the equine heart rate in the aerobic zone and occasionally the threshold zone. The aerobic zone occurs at 70-80% of the maximum heart rate and develops lung function, improves the ability to use oxygen to fuel movement, allows for the creation of new blood capillaries while aiding in performance. New blood capillaries formed in the muscle are extremely important for performance because the higher the ratio of capillaries to muscle fibers or weight, the more oxygen is carried in the bloodstream to these hyper-developed muscles. The aerobic zone is initially achieved through extended periods of a slow gallop. The threshold zone is met at 80-90% of the maximum heart rate. Working in the threshold zone delays the onset of fatigue during a race and improves cruising speed, which is tremendously significant for a 1-¼ mile race such as the Kentucky Derby. The threshold zone is achieved through speed work, such as what occurs during a breeze in between aerobic gallops. The end goal is to work in the threshold zone for a longer period during the workout as training time goes on. (Pressey, 2009)

Equine Heart Rate Monitor
Figure 1. Equine Heart Monitor

Another vital portion of heart rate monitoring and training occurs in recovery after the speed workout. The recovery zone is reached at 60-70% of maximum heart rate after a training session. Lactic acid is flushed away from the muscles, and recovery is enhanced. This zone is best used for 60-90 seconds after a breeze before exiting the track. (Pressey, 2009)

A quick and explosive start of the gate (Figure 2) requires the work of fast-twitch fibers, or type IIx muscle fibers. Type IIx fibers rely on anaerobic respiration to fuel the muscle contractions necessary to perform short-duration and high-intensity activities (Penney), such as short sprints. They are highly oxidative and rich in glycogen, which serves as an energy source in the case of sudden and strenuous activity (Curry et al.l).

Starting Gate
Figure 2. Starting Gate

As the anaerobic capacity of the type IIx fibers has been reached and the horse settles into stride, the workload shifts to the slow-twitch fibers, also known as type I muscle fibers (Harris). Type I fibers are recruited for lower-intensity, sustained activities (Penney). Their long and lean build provides a small diffusion distance for optimal oxygen transport. Type I fibers also have a rich capillary supply, aiding in the efficient oxygen transport required for aerobic respiration ("Introduction to Skeletal Muscle").

From breaking out of the gate with great power to maintaining a quick stride, and lastly giving a final burst of speed to the finish line, racehorses utilize both aerobic and anaerobic muscle fibers (Curry et al.). Because both are recruited while racing, having a conditioning program that facilitates both aerobic and anaerobic responses is critical to the success of the racehorse.

Thermoregulation is critical in a racehorse who generates quite a bit of energy in the form of heat. The five heat loss mechanisms in the horse are convection, conduction, direct radiation, evaporation of sweat, and respiratory loss (Figure 3). Convection is the heat generated from deep within the body that comes to the surface of the horse and out into the air. During cooler, windier days, the wind blows the heat away from the horse's body. On hot and humid days with little air movement, it is important to put the horse in front of a fan, which will blow the heat away from the surface of the horse to cool them off. Conduction and convection are alike. But conduction transfers the heat built up from the blood of the horse moving to the air. Conduction is inefficient on hot days because the temperature of the air is already high. Direct radiation is the heat coming off the horse, and it can be seen in the form of steam after a horse has worked hard on a cooler day. To make this process efficient, the horse should be moved to a shaded area. Evaporation of sweat is an additional way to keep a horse cool. When the animal sweats, it evaporates into the air causing the horse to cool down. Hot and humid climates make this process ineffective. Shady areas and fans are important in these climates. The final heat loss mechanism is respiratory loss. Although minimal, this is the process of losing heat while the horse exhales. (Majors, 2019)

Thermoregulation
Figure 3. Thermoregulation in a Horse

Strategies for thermoregulation include exercise condition, acclimatization, monitoring, diet change, and being aware of temperature and humidity. Training in environments similar to the competition environment helps condition a horse for a race. Three weeks before a race, the horse should be allowed to acclimatize to the new environment. If the animal is in a new environment it is very important to monitor their vitals such as temperature, heart rate, and respiration rate to make sure they remain in normal ranges. Changing some of the fiber in the horse's diet to fat reduces the amount of fermentation, which creates heat, that takes place during digestion. Lastly, checking the weather for temperature and humidity would help trainers and owners recognize what appropriate actions to take for the horse's wellbeing. (Majors, 2019)

To reach a level of training and improvement, a racehorse needs a special diet. The bulk of the diet is fibrous carbohydrates such as forages. For performance horses, the amount of forage consumed per day should equate to around 1-2% of the horse's body weight; for example, a racehorse that weighs 1,200 pounds should consume anywhere from 12 to 24 pounds of forage. (Kentucky Equine Research Staff). This includes timothy or oaten hay. If the racehorse receives no other feedstuff, then it should be at the upper end of the range. However, to provide an additional energy source for the racehorse throughout the day, an additional two to four pounds of an alfalfa mix is fed per day. Forages typically provide the horse its required protein intake. Too much excess protein causes water intake to increase as well as blood urea levels to increase which can result in intestinal disturbances. (Hoff). Horses have a huge capacity in their hindgut for fiber fermentation. This is what allows the horse energy that is being supplied long after the meal is eaten. Five to ten pounds per day of beet pulp, a highly digestible fiber, can be mixed in the diet. Beet pulp protects the horse from gastric ulcers and colic. (Hoff).

A diet consisting of hay alone leaves a racehorse with an energy deficit and the need of additional calories. Cereal grains, such as oats, corn and barley make up the starch in a racehorse's diet, a crucial energy source. (Kentucky Equine Research Staff). When cereal grains are digested, there is a direct rise in blood glucose and insulin, which are the two most important factors in glycogen synthesis. During high-intensity training and competitions, glycogen is a major fuel used in the muscles of racehorses. But too much starch can overflow into the cecum and colon causing acidosis. Acidosis kills the important microbial populations that live in the gut and help with normal digestion. The result is colic, anorexia, ulcers, wood-chewing, and weaving. (Hoff). To prevent such issues, it is recommended that a racehorse should not consume more than 5 pounds of grain in a single meal. (Kentucky Equine Research Staff).

Fats, vitamins, and minerals are also important in the racehorse diet. Fat supplies calories for lower intensity training and endurance. It also meets the racehorse's maintenance energy requirement and is very digestible. One half to two- and one-half cups of vegetable oil can be substituted in the diet, and it is 2.5 times and three times more digestible than corn and oats respectively. Vitamins and minerals facilitate the proper use of nutrients. (Hoff). A study mentioned in the Kentucky Equine Research Conference Proceedings in 2018 that thoroughbreds given a 5 mg chromium supplement from a chromium yeast product, had reduced lactate and cortisol production. (Pagan, J. D., et al.). Lactate causes sore muscles, which can lead to slower workouts and races. Cortisol is released during exercise which is a form of stress. Too much stress can cause dangerous biochemical responses that can cause damage to the horse's health.  Horses that are exercised strenuously, such as thoroughbreds, would benefit tremendously from the 5 mg chromium supplement. (Pagan, J. D., et al.).

Electrolytes are an essential part of the equine athlete's diet. Horses lose large amounts of electrolytes in sweat. This causes the electrolyte requirement of these animals to increase. According to Joe Pagan of Kentucky Equine Research Incorporated in Versailles, Kentucky, adequate intake of good-quality forage and free-choice salt satisfies the electrolyte requirement in lightly exercised horses. Thoroughbreds are more heavily exercised and therefore would need an additional potassium supplement to replenish the lost electrolytes. (Pagan).

All horses know how to run, but what does it take to produce a Kentucky Derby champion? An effective racehorse regimen not only focuses on training but also on dietary needs, health and safety. Each and every component is important and neglecting to give equal attention to all could hinder the potential and limit the success of the racehorse. By following a well-rounded program, with time, hard work and passion, winning "The Greatest Two Minutes in Sport" could easily become a reality.

Works Cited

  1. Berkland, Jill, and Loretta A. Berkland. Kentucky Derby: Racehorse Physiology. Mar. 2020.
  2. Breeders' Futurity at Keeneland, October 5, 2019: 10–4–2–1 Road to the Kentucky Derby Points: 2020 Kentucky Derby & Oaks: September 4th and 5th, 2020. At Keeneland, October 5, 2019 | 10-4-2-1 Road to the Kentucky Derby Points, 5 Oct. 2019.
  3. Curry, Jennifer Wendy, et al. High Oxidative Capacity and Type IIx Fibre Content in Springbok and Fallow Deer Skeletal Muscle Suggest Fast Sprinters with a Resistance to Fatigue. The Journal of Experimental Biology, vol. 215, ser. 22, 0 Nov. 2012, pp. 3997–4005. 22, doi:10.1242/jeb.073684
  4. Harris, Jaclyn. The Process of Training a Race Horse for the Kentucky Derby. Derby Experiences, Churchill Downs Incorporated, 23 Jan. 2015.
  5. Hoff, B. Lynne. Feeding Racehorses. BioEquine.
  6. Introduction to Skeletal Muscle. Lumen, Lumencandela.
  7. Kentucky Equine Research Staff. Effect of Strenuous Exercise on the Equine Respiratory System. Kentucky Equine Research, Kentucky Equine Research, 21 Dec. 2017,
  8. Kentucky Equine Research Staff. How Much Hay To Feed Horses: Where To Begin. Kentucky Equine Research, Kentucky Equine Research, 13 Sept. 2018, 
  9. Kentucky Equine Research Staff. Think Energy When Feeding the Racehorse. Kentucky Equine Research, Kentucky Equine Research Staff, 4 May 2018, 
  10. Majors, Sammi. Thermoregulation in Horses. Triple Crown Feed, Triple Crown: Always Beyond, 8 July 2019.
  11. Mendoza, Sigi. Understanding Thoroughbred Morning Workouts. Lady and The Track, 8 Dec. 2014.
  12. Pagan, J D, et al. The Effect of Chromium Supplementation on Metabolic Response to Exercise in Thoroughbred Horses. Kentucky Equine Research Conference, p. 147.
  13. Pagan, Joe. 18th Kentucky Equine Research Conference. Electrolytes-Critical-for-Performance-Horses. p. 67.
  14. Penney, Stacey. Fast-Twitch vs. Slow-Twitch Muscle Fiber Types + Training Tips. NASM, 22 July 2018.
  15. Polar Equine Heart Monitor. Polar, Polar USA.
  16. Pressey, B. Heart Rate Training Zones Explained. ThoroEdge Equine Performance, STORM, 4 Feb. 2009.
  17. Starting Gates of the Kentucky Derby. Kentucky Derby, Churchill Downs Incorporated.
  18. Thermoregulation. Veterian Key, 8 July 2016, https://veteriankey.com/thermoregulation

By Jill Berkland, Kayla Walter, and Peggy Auwerda.
The report is a project for ANS313 Exercise Physiology of Animals