Feeding Horses in Work – Nutritional Requirements & Example Diets

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

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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 electrolyte in the body. It is an extracellular anion that is important for maintaining acid-base balance. The requirement for exercising horses is up to 2.3x above maintenance.
• Potassium: Potassium is critical for muscle contraction and relaxation. The requirement for exercising horses is up to 2.1x above maintenance, but this mineral is typically oversupplied in the equine diet.
• Magnesium: Magnesium is essential for muscle relaxation and neural signalling. The requirement for exercising horses is up to two times above maintenance.
• Calcium: This macromineral is critical for muscle contraction and bone mineralization. The requirement for exercising horses is up to two times above maintenance. The calcium-to-phosphorus ratio in the diet should be between 1.5 – 4 to 1 in mature horses.

Antioxidants

Some vitamins and minerals have higher requirements in exercising horses because of their role as antioxidants.

Table 1: Daily minimum requirements for antioxidant nutrients for a 500 kg / 1,100 lb mature horse at maintenance and heavy exercise ^[6]

Other vitamins and minerals have greater requirements in exercising horses because of their roles as co-factors for enzymes involved in metabolic processes. Such nutrients include:

• Iodine
• Cobalt
• Thiamine (vitamin B1)
• Riboflavin (vitamin B2)

Increasing the levels of these micronutrients in the diet can help the horse use more of the energy provided by their feed.

How to Feed Performance Horses

The following feeding guidelines for performance horses are based on meeting the nutritional requirements as described by the NRC’s Nutrient Requirements of Horses.

The specifics of optimizing race day and training day diets should be tailored to the horse’s discipline and discussed with a nutritionist.

1) Maximize Forage Intake

Horses will naturally increase their total feed intake when their exercise level increases. Horses in very heavy exercise are expected to consume 2.5% of their body weight as dry matter compared to 2% for horses at maintenance. ^[6]

High forage intake does increase gut fill, which makes the horse heavier and has obvious implications for performance. Although reducing forage intake on race day can enhance performance, the benefit of reduced dead weight needs to be carefully weighed against possible gut health and behavioural issues.

Forage intake should be at least 1% of body weight (5 kg or 11 lb for a 500 kg / 1,100 lb horse) per day. ^[8]

If free-choice access to forage is provided, the performance horse can often meet or come close to meeting their energy and protein needs from forage alone.

Studies show that even racing Standardbreds (considered very heavy exercise) can maintain their body condition and exercise performance on all-forage diets. ^[9][10] However, it should be noted they were consuming forages with higher energy than typically available in North America.

Choosing Forage for Exercising Horses

Whatever your horse’s exercise level, select hay that will meet their energy needs with free-choice intake. For horses in moderate to very heavy work, this will likely require high-quality grass hay along with legume hay such as alfalfa.

When choosing hay for performance horses, look for hay harvested in early growth stages that is soft and has abundant leaves or blades. This will be more palatable than stemmy and coarse, helping to ensure the horse is eating enough to provide adequate energy and protein.

Pasture turnout is also a great way to support their natural behaviours and provides an energy-dense, cost-effective feed.

2) Add Fat and Fibre to Meet Energy Needs

Forage should make up the bulk of your horse’s diet and provide most of their digestible energy. Your horse may need additional energy sources if:

• They are underweight
• Forage quality is poor
• Forage availability is low

Monitor your horse’s body condition as an indicator of whether they are meeting their energy requirement. Exercise performance is best when body condition is 4 – 5 on the 9-point Henneke body condition scoring system. ^[7]

Performance horses should have additional energy needs met by sources that are high in soluble fibre or fat.

Choosing Fibre Sources

Soluble fibre is rapidly digested in the hindgut to generate short-chain fatty acids that are used as energy by the horse. On a forage analysis, the non-fibre carbohydrates (NFC) represent carbohydrates that provide rapidly available energy.

Beet pulp, a cost-effective by-product feed, is an excellent source of energy and has the additional benefit of a high water-carrying capacity. ^[11] This means it can also help prevent dehydration in exercising horses. However, it is high in calcium like alfalfa and should be balanced with a palatable phosphorus source such as wheat bran.

Choosing Fat Sources

Fat is the most calorie-dense energy source, providing 2.25 times more calories per gram than carbohydrates or protein.

Fat is also considered a cool energy source because it generates less heat during digestion, which is beneficial for performance horses. Reducing the reliance on grains as an energy source can also make horses less hot and easier to handle. ^[12]

Performance horses can have up to 20% of their digestible energy requirement met by fat, which represents roughly 700 ml (25 oz) of oil for a horse in very heavy exercise. ^[27] However, total replacement of all grains in the diet may not be suitable for all performance horses as grain feeding helps replenish glycogen lost during exercise.

When choosing an oil, look for sources of the omega-3 fatty acids, DHA and EPA. These are found in marine sources such as fish oil and microalgae, but not in plant-based oils such as flax or camelina oil.

DHA and EPA provide superior anti-inflammatory benefit compared to ALA and have been shown to support joint health, respiratory function, cardiovascular health, and reduce bleeding in performance horses. ^{[13][14][15][16]}

Mad Barn’s w-3 oil provides 1,500 mg of DHA per 100 ml serving from palatable microalgae.

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3) Choose grains carefully

Although forage-based diets can meet the energy needs of most horses, some horses may benefit from a low inclusion of grains.

Grains such as oats, barley, and corn are high in starch and sugars, which can be used to make glycogen in the muscle. Diets that have higher hydrolyzable carbohydrate content may result in greater repletion of muscle glycogen after exercise. ^[17]

However, excessive intake can be detrimental so the inclusion of these feeds should be carefully calculated based on your horse’s exercise level and the composition of their diet. Complete feeds are commonly fed to exercising horses but may result in overfeeding grains and underfeeding vitamins and minerals.

Work with a nutritionist to add precise amounts of grain to your horse’s ration. Oats are the preferred grain because they are higher in protein than barley and corn and the starch is better digested in the small intestine. ^[18] Feeding oats directly, instead of as part of a complete feed, gives you more control over the diet to meet your horse’s needs.

Strategies for grain feeding

Feeding grain as soon as possible after work will result in the highest repletion of glycogen in muscle. ^[28][29] Even horses with metabolic syndrome that have returned to significant work levels can tolerate, and often need, a feeding of oats plus alfalfa or beet pulp after exercise on days they work.

To increase both the fibre and hydrolyzable carbohydrates in the diet, feed a mash of 2 parts alfalfa and 1 part wheat bran, by weight. This boosts the nutritional value above alfalfa alone and corrects the calcium phosphorus ratio.

To avoid needing to soak the feed, consider a 2:1 mixture of plain oats and alfalfa. To get the most benefit from grain feeding it should be done as soon as possible after exercise is over.

4) Meet Vitamin & Mineral requirements

Given the high metabolic rate of exercising horses, it is especially important to meet all their vitamin and mineral requirements. ^[19]

Deficiencies in key vitamins or minerals can result in diminished performance, poor hoof or coat quality, slow workout recovery, changes in behaviour and an impaired immune response.

Mad Barn’s Omneity is a comprehensive vitamin and mineral supplement that helps to meet all of the micronutrient requirements of performance horses. Omneity is formulated with higher-quality organic trace minerals and provides full B-vitamin fortification, which is particularly important for horses in heavy work.

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Supplementing Electrolytes

For horses in light to moderate work, the main electrolyte that needs to be supplemented is sodium. This can easily be added to the diet by feeding salt. Salt also stimulates thirst to encourage water intake, which is beneficial for gut health.

In addition to free-choice loose salt, horses at maintenance should get:

• at least 2 tablespoons loose salt per day in cool weather
• at least 4 tablespoons loose salt per day in hot weather

Horses in heavy or very heavy work have significantly higher sodium requirements. Even with free-choice salt available, horses with high sodium requirements may not consume enough to fully meet their needs. ^[20] They likely also need other electrolytes supplemented to replace the losses in sweat.

Horses exercising in hot weather will sweat more and therefore lose more electrolytes that need to be replaced after exercise.

For exercising horses and those in hot weather, choose an electrolyte formulated specifically for horses with appropriate levels of sodium, calcium, potassium, and magnesium. A sugar source such as dextrose helps to increase the absorption of these nutrients and also provides a substrate for making glycogen. ^[21]

Electrolyte supplements should be given in addition to daily salt provisions to ensure the horse’s sodium and chloride requirements are met.

Mad Barn’s Performance XL is an electrolyte designed to meet the needs of high performance horses. Performance XL is scientifically formulated to replace the electrolytes lost in sweat and contains added Vitamin E and Vitamin C to support post-workout care.

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• Supports exercise performance
• Promote workout recovery

5) Support Gut and Respiratory Health

Given the high incidence of gut health and respiratory concerns in performance horses, you may want to consider supplements and management changes to support both digestion and breathing. It is estimated that up to 90% of performance horses have gastric ulcers, and roughly 40% have respiratory disease. ^[5][22]

Meeting the working horse’s vitamin and mineral requirements and feeding a forage-based diet can go a long way to reducing their risk of health concerns, but additional supplements may be warranted.

Supporting Gut Health

Before turning to supplements, some key management strategies can have significant benefits to gut health, including:

• Providing regular turnout with appropriate companions
• Providing free-choice hay or pasture whenever possible and ensuring they don’t go more than 3-4 hours without access to forage
• Replacing some or all concentrate feeds with fat or low-NSC fibre sources, such as beet pulp or soybean hulls
• Reducing environmental stressors

Because trailering and the associated stressors are unavoidable for competition horses, they will still have some risk of developing gut issues.

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Supporting Respiratory Health

Horses that are kept inside for most of the day are likely to develop respiratory issues due to dust and ammonia in the air. Respiratory irritants can be reduced in the environment by:

• Limiting protein oversupply to decrease urea excretion
• Using low-dust bedding
• Maximizing turnout
• Steaming the hay
• Ensuring moldy hay and feeds are not used

Supplements that support respiratory health include:

• Spirulina: A blue-green algae that is high in anti-oxidants (beta-carotene, vitamin C & vitamin E) and has anti-inflammatory properties.
• Jiaogulan: An herbal supplement purported to stimulate blood flow. The combination of 20 grams of spirulina and 2 grams of jiaogulan been shown to improve respiratory health in exercising horses and improve performance. ^[23] Jiaogulan (Gynostemma pentaphyllum) also attenuates inflammation in an asthma model and has bronchodilating effects. ^[30][31]
• DHA: This omega-3 fatty acid found in Mad Barn’s w-3 oil improved cough scores in horses with recurrent airway obstruction (RAO). ^[14][15]

For exercising horses that need extra calories, choose w-3 oil to provide calorie-dense fat and omega-3 DHA to support respiratory and joint health.

Example Diets

The example diets below consider a mature 500 kg / 1,100 lb horse in light, moderate, heavy or very heavy work. The primary goal of these diets is to meet their energy needs without over- or under-supplying digestible energy and fully balancing the diet with a complete vitamin/mineral supplement and salt.

Light Work

Horses in light work can meet their digestible energy needs from grass hay or mixed hay alone. These horses generally do not need a legume forage such as alfalfa or additional calories from grains or fats.

Pelleted Omneity and loose salt are sufficient to fully balance their hay.

Moderate work

To meet the elevated energy requirements for horses in moderate work, hay alone may not be sufficient. In this example diet, alfalfa cubes are used to boost the energy supply and as a carrier for added oil.

Visceral+ is added to support gut health as the risk of gastric ulcers increases with increased exercise load.

Heavy work

For horses in heavy work, alfalfa hay can be used to make up a portion of the forage. In this example diet, oats are also added to provide highly digestible carbohydrates.

These diets should be tailored to your horses discipline. Endurance horses vs racehorses will benefit from different diet formulations despite having the same nutritional requirements. This example diet is more appropriate for racehorses with higher levels of starch and sugar.

Very Heavy work

Horses in very heavy work can be maintained on a forage-based diet, with oil providing additional calories.

In this example diet, 600 ml (21 oz) of oil is included to meet increased energy needs from a cool energy source. Oil should be introduced gradually to avoid digestive upset, starting with 1 oz and increasing every 3-4 days.

Summary

Follow these steps to meet the nutritional needs of exercising horses and support performance:

• Ensuring forage intake is maximized from high-quality forages
• Using fibre and fat sources when additional calories are required
• Ensuring the diet is well-balanced with adequate vitamins and minerals, paying close attention to electrolytes and antioxidants

The best way to fine-tune your performance horse’s diet is to obtain a forage analysis and consult with an equine nutritionist. Your nutritionist will help you mitigate health concerns and optimize your horse’s exercise performance.