Excerpt from My Horse University’s Online Horse Nutrition Course
Horses eat to meet their energy requirements. Energy demands increase with workload, production status, and general demands of maintenance (energy needed for eating, digestion, regulating body temperature, etc).
Horses need energy for day to day maintenance, digestion of food, performance, reproduction and growth.
Horses utilize different feed components for energy that can either be used immediately or stored for later use. Thus they can get fat! Dietary carbohydrates, fats, and even proteins can all be used for energy. Carbohydrates provide the primary source of energy in the horse’s diet. A horse should receive at least 1% of its body weight in forage. Most horses will eat 1.5–2% of their body weight in forage to safely meet their energy needs.
Carbohydrates such as forage and energy grains make up the base of the horse’s diet. Horses require a minimum of 1% of their diet in forage.
Energy Needs of the Horse
Energy can be stored for later use in muscle glycogen, adipose tissue (fat), liver glycogen, and body protein (muscle tissue); but too much stored energy results in a fat horse. Overeating can lead to obesity, founder, and colic. If horses do not receive enough energy, their systems will sacrifice production. It is important to balance your horses’ diets in order to provide all of the nutrients without their eating too much or too little.
You've probably heard the word "calorie" when people are talking about gaining or losing weight. Many people know that there are almost no calories in a carrot stick while there are 250 or more calories in an average candy bar. But what is a calorie and why do we care? A calorie is a measure of energy provided by food. All living things have energy requirements. The goal is to balance the energy obtained through eating with the energy required by the body. In human nutrition, when the term calorie is used it actually refers to a "large" Calorie or kilocalorie (kcal) that equals 1000 [small] calories. In equine nutrition, since horses are quite large and have high energy requirements, mega calories or Mcals are used. One Mcal = 1000 kcals or 1,000,000 calories!
Measuring Energy in Horse Feeds
Digestible energy is measured in megacalories per kilogram of feed (Mcal/kg). The DE requirements for a 500 kg (1,102 lb) horse can range from 15.2 Mcals (minimum maintenance) to 34.5 Mcals (very heavy exercise). DE of feed can be determined by performing feeding trials on animals. The DE of a feed will differ for various species resulting from differences in the digestive functions of each. Since there are limited feeding trial data for horse feeds, the DE is estimated from their chemical composition using mathematical equations. Rather than trying to calculate these values yourself, the 2007 NRC offers an extensive table of nutritional information on a wide range of forages, grains and fats and oils.
Digestible Energy (DE) for horses of common feeds. Source: Committee on Nutrient Requirements of Horses, National Research Council, (2007). Nutrient Requirements of Horses: Sixth Revised Edition. Washington, DC: National Academies Press.
Energy from Fat
Fat is 2.25 times more energy dense than grains or proteins, meaning that fat provides a little more than twice as much digestible energy as an equivalent amount of protein or carbohydrates. Dietary fat can be used to increase the energy density in a horse’s diet. Cereal grain concentrates will average about 3% vegetable fat. Additional fat can be supplemented into the horse’s diet so that the concentrate can be up to 20% fat.
Commercial mixes with added dietary fat usually range from 5 to 10%. Supplementary fat in the diet reduces the overall quantity of concentrate consumed by a horse and can also increase coat luster. Added dietary fat in the diet may help horses that tie up or are prone to founder. When adding fat to the diet, it is important to balance the other nutrients for the added energy. For example, if corn oil is top dressed to an existing concentrate mix, the protein, minerals, and vitamins will become diluted because of the additional energy source. Balancing the diet for the other nutrients is especially important when feeding a high fat diet to a young growing horse.
Converting Protein to Energy
Significant amounts of protein will be converted to energy when there is excess dietary protein and or if the horse is extremely thin and there are no fat stores left, thus causing muscle tissue to be broken down and used for energy. The conversion of protein to energy results in byproducts including heat and ammonia. The ammonia is then converted to urea in the liver, which is excreted in the urine. These byproducts increase ammonia emissions into the air and can affect the air quality of stalled horses and ultimately reduce performance. Another thought to keep in mind is that for protein to be used, increased water intake is necessary to burn protein as energy.
Using protein as an energy source is expensive. High-protein feed offers nothing different than carbohydrates in terms of energy—in fact, the body breaks down excess protein to carbohydrates and urea. The carbohydrates are used for energy or changed to fat and stored, and the urea is passed in the urine. Why pay for expensive high protein feeds when you can get the same results with a lower-cost grain or forage?
Soybean meal is the major source of protein in commercial feeds.
Energy Excesses and Deficiencies
Dietary energy excesses lead to increasing stored energy in the body by way of depositing adipose or fat tissue. A fat horse has an increased likelihood of developing nutritionally-related diseases such as laminitis, metabolic disorders, and, in young growing horses, joint problems. Overweight horses are less athletic and have more trouble cooling down during exercise, especially in hot climates.
An overweight horse is more prone to nutritionally-related diseases.
By contrast, energy deficiency means the horse will have decreased stored energy, resulting in decreased stamina and performance. Young horses will have poor growth rates, and broodmares and stallions will have poor reproductive performance. In addition, if there is no fat tissue to pull from, muscle tissue will be broken down and converted to energy, causing blood metabolism to become more acidic and decreasing the horse’s overall muscle mass.
A thin horse has no energy reserves for growth, performance or reproduction.
While weighing a horse can help you monitor weight loss and gain, it is impractical in most cases to have a scale big enough to accommodate a horse! Using weight tapes and calculating weight by a series of measurements is one way to estimate a horse’s weight. Still, these values don’t really reveal how much fat tissue a horse has. Body Condition Scoring is an effective tool to monitor a horse’s body fat stores. For the average farm it is the best tool to monitor energy intake in the horse.
View this video What’s Your Horse’s Body Condition Score with Dr. Bob Coleman from University of Kentucky.
How to Body Condition Score Horses. eXtension.org Horses Learning Lesson. 11/2/12
Mowrey, Robert. High Fat Diets for Horses. eXtension.org/horses Article. 11/2/12.
Nutrient Requirements of Horses. Sixth Revised Edition. 2007. Academic Press.