Horses need nutrients to be healthy. The horse’s diet must meet the animal’s requirements for five basic nutrients:  

  • Water—approximately five to 10 gallons per day, but this varies greatly depending on the animal’s size and weight, environmental temperature, type and amount of foodstuff consumed, and the amount of exercise, work, or production  
  • Protein—approximately 8-15% of a horse’s dietary needs  
  • Vitamins—approximately 1% of a horse’s dietary needs  
  • Minerals—approximately 2-3% of a horse’s dietary needs  
  • Energy—approximately 80-90% of a horse’s dietary needs. While energy itself is not a nutrient, there are “energy-producing nutrients” that are fed to horses, including: 
    • carbohydrates, 
    • starch, 
    • sugar, 
    • fiber or cellulose (the “fibrous” part of plants), and 
    • fat.  

The intake of these nutrients in the proper amounts and proportions makes it possible for the horse to perform the functions of:  

  • maintenance, 
  • growth, 
  • production (fitting/fattening, reproduction and/or lactation), and  
  • work.  

Water  

Horses, like other living things, cannot live without water. Water is needed to carry other nutrients throughout the body and to help regulate body temperature. Approximately 65-75% of a horse’s total body weight is made up of water. If a horse loses 10% of its body water, serious conditions can result. The loss of 20% of body water can result in death! 

A 1,000-pound equine typically consumes anywhere from five to 10 gallons of water per day. Intake varies from animal to animal and is affected by environmental temperature, exercise, type of food being consumed, age, health, pregnancy, or lactation, etc.  

Water is contained in all cells and fluids in the body and is essential for the following: 

  • production of saliva  
  • regulation of body temperature  
  • chemical reactions involved in digestion, absorption, and metabolism  
  • normal cell function  
  • lubrication of different body parts and systems for normal function of joints, hearing, central nervous system, sight, and more.

Horses obtain some water from within their bodies as a result of digestive and metabolic reactions that take place inside the body to support its functioning. When the body processes proteins, carbohydrates, and fats, “metabolic water” is an end result.  

Any excess water in the horse’s body is excreted in urine, feces, sweat, and from the lungs as water vapor—a byproduct of respiration.  

Issues with Lack of Water

Serious health problems, such as impaction colic and dehydration, can result from a lack of water. Therefore, it is essential that horses have clean, fresh water available at all times. In colder climates, for example, the temperature of available water can cause horses to limit their intake. A severe form of colic, known as impaction colic, can result if caretakers do not ensure that a horse drinks adequate amounts of water. 

There are only a few situations in which water should be limited and not offered “free choice” to horses. Hot, heavily exercised horses should not be allowed access to large quantities of water. Instead, they should be offered small amounts over a period of time, allowing the body to return gradually to a more normal temperature—a process known as “cooling out.”  

With certain types of colic, the intake of additional water can actually worsen the problem; therefore, always consult a veterinarian if you suspect colic.  

Another example where water intake might need to be monitored and/or reduced would be just prior to a race or other intense physical exercise. In those cases, the intake of large amounts of water might need to be limited.  

Horses’ Nutrients Include Protein  

Protein, a vital component in all animals’ diets, should make up 8-15% of a horse’s ration.  

Proteins are made up of a “chain” of many smaller parts known as amino acids. Different proteins contain different amino acids. (An analogy made by Lon D. Lewis in his equine nutrition book, “Feeding and Care of the Horse,” is that “if amino acids were letters in the alphabet, proteins would be words.”)  

The amino acids are often referred to as the “building blocks” of the body. They are the basic materials from which bone, muscle, and soft tissue are “built.” Amino acids make up enzymes, blood, hormones, hoof, hair, and more.  

In nature, there are 22 different amino acids that exist and can make up protein chains. All amino acids include carbon, oxygen, and hydrogen molecules. What makes them different from carbohydrates or fat is that amino acids also include a nitrogen molecule—and in some cases they include a sulfur, phosphorous, or iron molecule.   

Use of Proteins

During the process of digestion, enzymes and acids in the horse’s digestive tract break down protein in foodstuffs into the amino acids that make up the protein’s chain. The amino acids are absorbed through the wall of the small intestine and into the bloodstream by way of the liver. The amino acids are then sent in all directions throughout the body. At this point, they are still mostly in the same form as when they were absorbed in the small intestine.  

The horse’s body has the ability to change (“synthesize”) some amino acids into different amino acids when the body needs them. However, it cannot synthesize all of the amino acids needed to run its very complicated body systems. The amino acids that cannot be synthesized in sufficient amounts are known as essential amino acids. These amino acids must be supplied by a protein source in the horse’s diet. (The amino acids that can be synthesized within the body are called the non-essential amino acids.)  

Today, most commercial feed products are formulated to include essential amino acids. The essential amino acids are particularly important to young, growing equines.  

Protein as an Energy Source

Protein can also be an energy source. However, fat and carbohydrates are much more efficient energy sources, as they produce much less heat while being turned into energy. The excessive heat produced by the body when breaking protein down into energy might be acceptable in the cold months, but it could be detrimental to a horse doing hard work in the warmer months of the year. Heat exhaustion could result. Thus, feeding protein is not an efficient way of delivering energy to the body.  

The protein that is not broken down into amino acids and absorbed in the horse’s gastrointestinal (GI) tract is not stored as protein in the body. Instead, it is chemically broken down, releasing the nitrogen, carbon, hydrogen, and oxygen molecules from the amino acids that make up the protein chain. The nitrogen released from this breakdown is excreted from the body in the urine. The carbon, hydrogen, and oxygen molecules are stored in the body and available to be used as sources of energy by the horse.  

CP and DCP

There are two terms that horse owners should be familiar with when talking about protein sources in a horse’s diet:  

  • Crude protein (CP)—This number estimates all of the nitrogen content of the feedstuff. Crude protein is not a good estimate of how much of the nitrogen in the feedstuff is from a protein source, or of how much would actually be available to the horse during the process of digestion.  
  • Digestible crude protein (DCP)—This number represents protein content based upon nitrogen content in the feedstuff. Digestible crude protein estimates what would actually be available to the horse during the process of digestion.  

Both crude protein and digestible crude protein are expressed as percentages.  

Urea is an inexpensive “non-protein” source of nitrogen that is added to many livestock/animal rations. Bacteria in the rumen (first stomach) of cattle and other “ruminant” livestock easily process urea. However, the horse has no rumen and in general cannot utilize urea. In fact, urea can be toxic to horses, especially to growing animals. Therefore, even though it might be cheap and readily available, horse owners need to understand that it is not a good source of nitrogen for horses.   

Lack of Protein

A lack of adequate protein in a horse’s diet can produce any or all of the following effects:  

  • decreased growth rates  
  • decreased appetite  
  • body tissue loss  
  • muscle loss  
  • slow hoof growth  
  • poor hair coat  
  • lack of energy to do work or perform at peak performance levels .

The lack of adequate and quality protein in young, growing animals can have permanent negative effects. Remember, protein and the amino acids contained in protein are the building blocks of the animal’s body. Protein can be supplied and/or added to the horse’s diet in many ways.  

Sources of Protein

Some plant sources of protein include:  

  • Forages—from pasture or hay (dried grass hay, such as timothy, or legumes, such as alfalfa)  
  • Grains—cereal grains such as oats, corn, sorghum, barley, wheat, or rye   
  • High-protein sources—soybean meal and canola meal are the best high-protein sources for horses, due to their amino-acid content and balance; other choices include linseed meal, cottonseed meal, corn gluten meal, sunflower meal, brewer’s yeast, rice bran, etc.  
  • Some animal sources of protein:  
  • Milk protein—from milk sources or milk-processing byproducts (such as whey)  
  • Egg protein—from egg products  
  • Fish meal—from fish or fish processing byproducts  
  • Meat-industry waste products—from meat products or meat processing byproducts (such as bone meal and blood meal).  

Further Reading

Adapted from Equine Science: Basic Knowledge for Horse People of All Ages.