Phosphorus

Phosphorus is an essential macromineral required for numerous physiological functions in horses, including energy metabolism, bone formation, and cellular signaling. It is a component of adenosine triphosphate (ATP), nucleic acids, and phospholipids, and works in close association with calcium to support skeletal health. In the equine body, approximately 80% of total phosphorus is stored in the bones and teeth.

Dietary phosphorus is supplied through both natural feed ingredients and inorganic mineral sources. Common feed-based sources include cereal grains and their byproducts (such as bran), which contain phosphorus largely in the form of phytate—a form that is poorly bioavailable to horses. Inorganic phosphorus sources, such as monosodium phosphate or dicalcium phosphate, are often added to balanced rations to meet specific nutrient requirements and improve bioavailability.

The calcium-to-phosphorus ratio is a critical consideration in equine diets. An ideal ratio typically ranges from 1.2:1 to 2:1, depending on the horse’s age and physiological status. Excessive phosphorus intake, especially when calcium is deficient, can interfere with calcium absorption and contribute to conditions such as nutritional secondary hyperparathyroidism. Therefore, phosphorus levels must be carefully balanced within the overall mineral profile of the diet.