Horse feed can be divided into five main types of essentail nutrients. Each type has a different job in the horse's body. The five types are:

• Energy nutrients (carbohydrates and fats)
• Proteins
• Vitamins
• Minerals
• Water

If one of the essential nutrients is provided in a limited amount, it will be responsible for limiting the functions of the others even though the others are provided in adequate amounts. Energy is sometimes referred to as Total Digestible Nutrients (TDN). Some nutrition references will measure energy in calories or megacalories.

Energy can be defined as the ability to do work. This work can be in the form of the horse simply maintaining itself when it is doing nothing more then standing in a stall or in the pasture grazing, or it can be physical work if you are riding the horse regularily. Other types of work may be growth, a Mare creating a Foal during gestation and the work that is necessary for the mare to produce milk during lactation.

Obviously the level of energy that is required for the horse will change depending on the types and amounts of activity that the horse is involved in, the conditions in which it is living and the stage of development that it is in.

Proteins (Hay)
Proteins are highly complex. During digestion, proteins are broken down into amino acids. These are absorbed from the intestine into the blood stream and carried to all parts of the body. They are recombined to form body tissue and eventually become muscle, internal organs, blood, bone, skin, hair, hooves and many other parts of the body.

Minerals
The mineral content in feed can be determined by chemical analysis. Because the quality and type of hay available to horses changes throughout the year, these minerals should be made available in the form of dicalcium phosphate on a free choice basis.

Vitamins
Horses only need vitamins in small amounts. They are also essential to the normal body functions and the lack of these may cause diseases. The vitamins are A, C, D, E and the B complex. Most of the vitamins will be recieved in adequate amounts if the horse is provided the proper amount of feed. The two vitamins which have the potential of being lacked in the horse are vitamins A and D.

Supplement vitamin A (and carotene) are available in dehydrated alfalfa meal. It is found in some horse rations (sweet feed) and is also available in crystalline performed vitamin A. Caution must be exercised when adding this to a horse's diet because excessive use over extended periods may cause a condition similar to that of a vitamin deficiency. Good quality forage, including bran, should provide for the horse's B complex and vitamin E requirements. Vitamin B is also synthesised by bacterial action in the horse's gut, therefore there is rarely a deficiency in the horse.

Sunshine and sun-cured hay are good sources of vitamin D. Vitamin D is manufactured in the skin by exposure to ultraviolet radiation. Several hours outdoors in the sunlight should enable a horse to accumulate adequate spplies. Vitamin D is also available in cod liver oil.