Racehorses are remarkable creatures, almost artistic in their design. Their impressive lung capacity, incredible strength, and marvellous thoroughbred heart all contribute to their natural ability to run at astonishing speeds. When examining the physiology of a racehorse, it becomes clear how they can achieve feats like winning prestigious races like the Kentucky Derby.
Caloric necessities
Racehorses have significantly higher caloric needs compared to regular horses. A typical racehorse may require around 35,000 calories per day, which is roughly double the amount needed by a regular horse grazing in a pasture. This means that a 1000-pound racehorse would need to consume over 20 pounds of hay per day, in addition to a substantial amount of high-calorie concentrated feeds like grains and oats.
The specific feeding regimen can vary between trainers, but these high-calorie concentrates are generally a combination of fortified feeds, grains, and oats. Racehorses require a balanced diet of carbohydrates, proteins, and fats to maintain their energy levels and support their musculoskeletal system. However, since races involve short periods of intense exercise, racehorses' diets will likely have significantly higher starch levels compared to what would be considered healthy for the average horse.
On non-race days, research suggests that racehorses may benefit from diets with lower starch and higher fat levels. This can help prevent digestive issues and maintain steady energy levels. Additionally, fats generally have twice as many calories per unit as starch, making them a more efficient way to provide the necessary calories without increasing the overall volume of feed.
Fats also play an important role in maintaining the health of a racehorse's skin and coat.
Breathing Capacity
Racehorses' ability to maximise their oxygen intake is a crucial factor in their performance. Horses can move up to 1,800 litres of air per minute, which is enough to fill over 250 balloons during a race like the Kentucky Derby. Oxygen is required for the chemical process that converts glucose into energy, so greater oxygen intake provides more energy for the muscles.
Inflammation in the lungs can impair a horse's breathing and oxygen absorption. Research has shown that certain ingredients like plasma proteins and amino acids can help reduce lung inflammation. However, the intense pressure from strenuous exercise can still cause small blood vessels in the lungs to burst, leading to Exercise Induced Pulmonary Hemorrhage (EIPH), or bleeding in the lungs and airways.
It's estimated that a small percentage, around 0.15-0.84%, of racehorses experience EIPH, with the most severe cases (graded 4) being less likely to finish in the top positions. To make racing more transparent, the diuretic drug Furosemide (Lasix) used to treat EIPH has been banned from many major races. While this raises concerns about dehydration, there are also nutritional approaches like antioxidants that can help manage bleeding issues in racehorses.
Horse Heart
Even before scientific evidence existed, Thoroughbred racehorses with large hearts were believed to have an advantage and be more likely to win races. The size of a racehorse's heart is thought to be primarily influenced by the X chromosome, leading to the idea of an "X-factor" that produces big hearts in these horses.
Recent research has found connections between a large heart capacity and race wins. However, bigger is not always better when it comes to heart size. Heart enlargement can also occur due to disease, such as congestive heart failure, which makes the heart less efficient. Secretariat's heart, for example, was reported to be twice the size of the average racehorse at 22 pounds - about the size of a large Thanksgiving turkey. This was 20% larger than his rival Sham, even though the two horses were the same height.
In contrast, the human heart is relatively small, weighing just half a pound, about the size of a large apple. Effective circulation and delivery of oxygen-rich blood to the muscles are key to heart function. Horses benefit from nitric oxide in their bodies, which helps keep their tiny blood vessels, or capillaries, strong and healthy.
Hard Working Muscle
Similar to how a car reaches its top speed by revving its engine, a racehorse's heart rate increases to help it perform at its peak during a race. When a racehorse's heart beats faster, it can pump up to four times more blood, delivering more oxygen and nutrients to the muscles.
To maintain a healthy heart rate, a racehorse's diet should include antioxidants like vitamin E and selenium, which can protect the cells from damage and support heart health. It's also crucial to keep the horse well hydrated, as dehydration can stress the heart by reducing blood volume, increasing heart rate and blood pressure, and making it harder for the heart to pump effectively. Providing clean, fresh water is essential. During hot weather or strenuous exercise, most horses will require electrolyte supplements to replenish key nutrients lost through sweating.
Heat Energy
Thoroughbred racehorses generate a significant amount of heat energy, around 1,250 kilojoules per minute, during a race. This level of energy output is impressive, but it also puts these horses at a higher risk of developing exertional heat illness (EHI). EHI is a type of heat stress that occurs specifically during intense physical activity.
Racehorses produce a tremendous amount of body heat, making proper hydration and cooling procedures crucial to prevent EHI. Symptoms of EHI include dehydration, muscle cramps, and in severe cases, organ failure. Research has shown that horses who have previously experienced EHI are nearly 19 times more likely to have it again. Additionally, the study found that horses were slightly less likely to develop EHI if the weather leading up to the race was consistent, suggesting that acclimation to warmer temperatures may be a factor.
To prevent EHI, it is important to provide racehorses with adequate hydration and cooling measures, such as cold water baths and fans, to help regulate their body temperature. Studies indicate that supplementing horses with Chromium Propionate may also help them regulate their body temperature more efficiently during exercise. Chromium Propionate is a mineral that can help horses convert glucose into energy more effectively, which can reduce the amount of heat produced during this process. This mineral is approved for use in horses by the FDA and can be administered through feed or as a supplement.
Water Consumption
Studies have shown that racehorses can experience substantial weight loss during races and high-intensity exercise. One study published in the Journal of Equine Veterinary Science tracked changes in body weight and hydration status of racehorses during a simulated 1600-meter race. The average Thoroughbred lost 2.8% of their body weight, with some horses losing up to 6.8%.
Other studies have reported similar ranges, with averages closer to 5% weight loss and highest losses up to 11%, which can equate to 50 to 110 pounds for a typical 1000 lb racehorse. While this is significant, the majority of the weight loss is due to water loss through sweating. If the racehorse is properly hydrated and physically fit, they can typically regain the lost weight within a couple of days, with some fully recovering within 24 hours.
Even horses that don't exercise at the elite level of racehorses can experience similar weight losses due to other stressors, like transportation. Research has shown horses can lose 0.45 to 0.55% of their total body weight per hour of transport, meaning a horse could lose over 30 pounds during a 5-hour trip. Proper hydration is crucial before, during, and after travel or exercise to prevent excessive weight loss.
To ensure adequate hydration, horses should have access to clean water 24/7. The average horse, not at work, drinks 5-7 gallons per day, but this can increase to over 20 gallons per day in high temperatures. Electrolyte supplements, including sodium, chloride, potassium, chromium propionate, magnesium, and calcium, can also help support muscle recovery following exercise or heat stress.
Feeding a high-performance racehorse is a complex task that requires significant knowledge and experience to provide the best diet for speed and health.