In horses, as in humans, too much or too little can lead to serious health problems. Horses need a good supply of clean water daily. Water is essential for all body functions, including temperature regulation and feed digestion. The amount of water needed depends on the level of exercise, the ambient temperature, the quality of the feeds in the ration, and the proportion of the diet that is forage. This is the nutrient that primarily determines the weight and condition of the horse.
Energy is derived primarily from carbohydrates, fats, and any protein excesses.
Energy is needed for body functions, including maintenance, temperature regulation, digestion, work, etc. All energy that is provided above that which is needed will go toward the formation of fat. Prolonged deficiencies will result in unthriftiness and starvation. The body needs proteins for muscle and bone growth, milk production, fetal growth, and normal metabolism. The requirements of many horses, especially those in the maintenance, early pregnancy, and exercise classifications, can be met with good quality hay or pasture forage.