English
Performance horses have higher energy and protein requirements than horses at maintenance (not exercising).
Formulating diets to meet the requirements of horses in work should take into account their level of work and performance goals, as well as help mitigate the increased risk of certain health conditions that come with exercise.
Most horses in work can meet their energy and protein needs from high-quality forages. However, additional sources may be required to fully meet their needs.
Optimizing the diet of any performance horse also needs to take into account their discipline, breed, age, training/racing schedule, frequency of travel, and health history.
For example, although endurance horses and racehorses have similar nutritional requirements based on the NRC’s Nutrient Requirements of Horses, approaches to meet these needs will differ to best support their performance and recovery.
Consult with an equine nutritionist to develop a nutritional plan specific to your horse and your management & performance goals.
Equine Exercise Physiology
Horses evolved as a prey species that used their high capacity for intense exercise to escape predators. They also adapted to maintaining exercise endurance over long distances as they roamed expansive prairies in search of forages and water.
Since domestication, breeding to select for improved performance has produced breeds tailored toward specific forms of exercise.
Thoroughbreds have relatively little genetic diversity and are geared to short bursts of intense exercise. Conversely, Arabians are more suited to endurance exercise, and draft breeds excel at hauling heavy loads. [1]
All forms of exercise involve coordinated muscle contractions that use cellular energy in the form of ATP (adenosine triphosphate). ATP is the fuel that muscles use to contract and relax.
This energy comes mostly from breaking down fat and carbohydrates supplied by the diet and stored in the body. To a lesser extent, protein can also provide energy.
Some glucose (carbohydrate) is always being burned but fat predominates at rest and for low level exercise. This energy is generated aerobically (with oxygen) in the mitochondria.
As work intensity increases, the mitochondrial pathway may not be adequate so anaerobic (without oxygen) burning of glucose becomes a major contributor. Glucose is derived from glycogen stored in muscle or delivered by the blood to muscle.
Exercise Performance
In addition to training and conditioning, your horse’s feeding program plays a crucial role in supporting equine exercise performance.
Other aspects of equine management must also be considered to promote optimal performance. Some of these factors include supporting gut health, respiratory health, antioxidant status, post-workout recovery, electrolyte balance and immune function.
Maintaining Optimal Body Condition
Excess body condition (ie. fat coverage on the body) can affect performance by increasing the weight that needs to be moved and by making it harder to dissipate heat.
However, being too lean is also detrimental as it means there are less energy reserves available. A study in endurance horses found lower rates of completion of races with body condition score below 4.5. [24]
The ideal body condition score to support health and performance is 4.5 – 5 on the 9-point Henneke body condition scale. Although some disciplines may aesthetically prefer over-conditioned horses, this is not recommended on a health basis.
Minimizing stress
Chronic stress can significantly impact your horse’s well-being by affecting their appetite, compromising gut health, and reducing performance. Common sources of stress for exercising horses include: [2]
- Excessive exercise
- Frequent trailering
- Sleep deprivation
- Social isolation
- Frequent changes to social grouping
Exercise Level
To provide appropriate amounts of caloric energy in a working horse’s diet, their exercise level needs to be properly categorized. It is common for horse owners to overestimate the level of work their horse is engaged in. [3]
Horses that are miscategorized may be overfed grains and concentrates, contributing to the high incidence of gastric ulcers and hot behaviour in performance horses. [4][5]
The five levels of exercise established by the NRC are primarily based on the heart rate achieved during exercise and the duration of exercise. [6][7]
Maintenance
Horses at maintenance are not engaged in any exercise program. This includes horses turned out on pasture, who will naturally participate in some periods of increased activity while on pasture.
Light Exercise
Description: 1–3 hours per week; 40% walk, 50% trot, 10% canter. Heart rate during work is approximately 80 beats per minute.
Examples:
- Recreational riding
- Beginning of training
- Show horses (occassional)
Moderate Exercise
Description: 3–5 hours per week; 30% walk, 55% trot, 10% canter, 5% low jumping, cutting, other skill work. Heart rate during work is approximately 90 beats per minute.
Examples:
- Recreational riding
- School horses
- Show horses (frequent)
- Polo
Heavy Exercise
Description: 4–5 hours per week; 20% walk, 50% trot, 15% canter, 15% gallop, jumping, other skill work. Heart rate during work is approximately 110 beats per minute.
Examples:
- Ranch work
- Polo
- Low-medium level eventing
- Race training (middle stages)
Very Heavy Exercise
Description: Various; ranges from 1 hour per week speed work to 6–12 hours per week slow work. Heart rate during work is approximately 110 – 150 beats per minute.
Examples:
- Racing (Quarter horse, Thoroughbred, Standardbred)
- Endurance
- Elite 3-day eventing
Interpretation
These descriptions are intended as general guidelines and don’t describe every possible training program. The majority of horses in work will fall within light to heavy work.
Note that several disciplines are missing from the NRC guidelines, including dressage and reining.
Heart Rate during Exercise
When determining nutritional requirements, the main factor to consider is average heart rate during exercise. This is an indicator of how much caloric energy the horse is using during work and how much should be fed to maintain their body condition and support their exercise level.
Several other factors will also affect the caloric needs of performance horses, including: [7]
- Level of fitness & skill
- Speed
- Breed
- Temperament
- Weight of the horse
- Weight of tack & rider
- Weight being pulled
- Hills vs flatwork
- Footing
- Ambient temperature
When formulating a diet for performance horses, your equine nutritionist can help you categorize your horse into the appropriate level of exercise by taking into account these variables.
Nutritional Requirements by Exercise Level
1) Digestible Energy
The nutritional requirement that changes the most with exercise is digestible energy. This refers to the energy available for digestion and absorption after fecal losses are taken into account.
The exercising horse needs to consume enough energy to support basal metabolic processes, the additional demands of exercise, and muscle repair following exercise.
In North America, the energy requirement is generally expressed as megacalories (mcal) per kg of body weight.
For a 500 kg / 1,100 lb mature horse, the digestible energy requirements by exercise level are as follows: [6]
- Maintenence: 16.65 mcal / day
- Light Exercise: 19.98 mcal / day (20% above maintenance)
- Moderate Exercise: 23.3 mcal / day (40% above maintenance)
- Heavy Exercise: 26.6 mcal / day (60% above maintenance)
- Very Heavy Exercise: 31.6 mcal / day (90% above maintenance)
These requirements are based on evidence from experimental studies and field surveys and align well with observed energy intakes in horses of varying exercise levels. [7]
2) Protein
Protein requirements increase with exercise to build and maintain the larger muscle mass in conditioned horses, support muscle repair after exercise, and replace nitrogen losses in sweat. [6]
Assuming a 500 kg / 1,100 lb mature horse, the protein requirements by exercise level are: [6]
- Maintenance: 630 grams / day
- Light Exercise: 700 grams / day (11% above maintenance)
- Moderate Exercise: 768 grams / day (22% above maintenance)
- Heavy Exercise: 862 grams / day (37% above maintenance)
- Very Heavy Exercise: 1004 grams / day (60% above maintenance)
More recent research suggests these protein intakes recommended by the NRC may not be optimal for performance horses.
In one study, eventing horses (moderate or heavy work) had maximal protein and fibre digestibility when the diet provided 2.25 g crude protein per kg of body weight. [25] This would be 1125 grams per day for a 500 kg horse, considerably higher than the current NRC recommendation.
However, this doesn’t necessarily mean that high protein feeds must be added to the diet. Horses will naturally increase their forage intake when their workload increases. This can largely provide the extra protein they need.
For example, a 500 kg horse in heavy work is expected to consume 2.5% of their body weight in feed / forage. [6] This is up from 2% for a horse at maintenance.
If they are given an average quality forage (10% crude protein), their protein intake will be 1250 grams per day from forage alone, already above their NRC requirement.
There are some horses that are most likely to require additional protein – young exercising horses who have not reached maturity. Young, growing horses should have their protein intake carefully evaluated to ensure they are consuming enough protein and that it is of high-quality.
3) Amino Acids
Dietary proteins are made up of building blocks called amino acids. These molecules are used to make protein in the muscle and other parts of the body.
There are 21 different amino acids, of which ten can not be made in the body and must be provided in the diet. These are called “essential” amino acids, and horses also have a dietary requirement for these.
Scientifically, only the lysine requirement has been established in horses. This is considered the first limiting amino acid as it is most likely to be deficient in the diet, slowing down the rate of protein synthesis. The amino acids threonine and methionine are usually considered the second and third limiting amino acids for growing horses.
With exercise, the horse’s protein and lysine requirements increase. The lysine requirement is always calculated as 4.3% of crude protein. [6]
Assuming a 500 kg / 1,100 lb mature horse, the lysine requirements by exercise level are:
- Maintenence: 27 grams / day
- Light Exercise: 30 grams / day (11% above maintenance)
- Moderate Exercise: 33 grams / day (22% above maintenance)
- Heavy Exercise: 37 grams / day (37% above maintenance)
- Very Heavy Exercise: 43 grams / day (60% above maintenance)
Depending on the total protein supply of the diet, its digestibility, and its amino acid composition, you may or may not be supplying enough of the essential amino acids.
The sulfur-containing amino acid methionine is critical for healthy hooves. It is also needed to synthesize creatine and carnitine in muscles, which are involved in energy metabolism. However, sulfur levels in soil have been progressively declining over the last century which may result in decreased methionine in plants and put horses at greater risk of methionine deficit. [26]
Horses with poor topline may require additional protein sources or amino acid supplementation. Other signs of protein deficiency are poor hoof growth, slow hair growth, and reduced appetite. [6]
4) Vitamins & Minerals
Vitamins and minerals perform critical roles related to exercise, including:
- Acting as enzyme co-factors to support energy metabolism and protein synthesis
- Acting as anti-oxidants (vitamins) or as the active centers of antioxidant enzyme systems (minerals). These neutralize toxic free radicals produced during exercise
- Enable muscle contraction and nerve impulses (i.e. calcium within muscle and nerve cells) and to regulate those processes (magnesium)
- Enhance bone density to maintain a strong skeleton
- Enable water loss for sweating
- Act as electrolytes to maintain fluid balance and blood pH
Much of the research on mineral and vitamin requirements in exercising horses is focused on the roles of these nutrients as electrolytes and antioxidants.
Electrolytes
The following minerals are key electrolytes for exercising horses: [6]
- Sodium: Sodium is the most abundant electrolyte in the body. It is involved in conveying neural signals, stimulating thirst and maintaining fluid volume. The requirement for exercising horses is up to four times above maintenance.
- Chloride: Chloride is the second most abundant electrol