Phosphorus is one of the most important minerals in animal nutrition. It is the second most abundant element in an animal body after calcium, with 80% of phosphorus found in the bones and teeth, and the rest in the body fluids and soft tissue.
Phosphorus plays a key metabolic role and has more physiological functions than any other mineral. These functions involve major metabolic processes such as:
Development and maintenance of skeletal tissue: the greatest proportion of phosphorus is devoted to maintaining and supporting the skeleton, where it is co-precipitated with calcium in the form of hydroxyapatite. The skeleton acts not only as a support system but also as a reservoir of calcium and phosphorus from which the rest of the body can draw. It undergoes a continuous process of absorption and release of calcium and phosphorus, particularly during animal pregnancy and lactation and, for hens, during the laying period.
Maintenance of osmotic pressure and acid-base balance: together with other minerals, phosphorus has a major role in the maintenance of osmotic pressure, buffer capacity and acid-base balance.
Energy utilisation and transfer: phosphorus plays a vital part in energy regulation. Certain phosphates, such as adenosine triphosphate (ATP), are universal accumulators and donors of energy; they are present in all body cells and ensure both the storage of energy and its utilisation. ATP is of prime importance in muscular activity during which chemical energy is converted into mechanical energy.
Protein synthesis, transport of fatty acids, amino acid exchange: phosphorus compounds are involved, directly or indirectly, in all major physiological functions. Phosphorylation is responsible for intestinal absorption, glycolysis and direct oxidation of carbohydrates, renal excretion, transport of lipids, exchange of amino acids, etc. Phosphorus is also a component of numerous co-enzymes.
Growth and cell differentiation (DNA): phosphorus forms part of the structure of nucleic acids, which are carriers of genetic information and regulate protein biosynthesis and immunity.
Appetite control, efficiency of feed utilisation, and fertility.
An adequate supply of phosphorus, in a form that can be absorbed by the animal and is available for storage or use to support these physiological processes, is essential if optimal livestock health and productivity are to be achieved. This is often referred to as biologically “digestible” or “available” phosphorus.
In addition, an animal’s phosphorus requirement cannot be looked at in isolation, since both calcium and vitamin D are closely linked with it in many of the metabolic processes. For example, accretion of phosphorus in the animal’s bones is also affected by the presence of calcium and vitamin D.
Consequently, in addition to adequate phosphorus levels, the calcium to phosphorus ratio (Ca:P), as well as suitable levels of vitamin D, are critical to balanced nutrition.