Importance of Phosphorus
Phosphorus (P) is an essential element for appropriate growth, development, and production. Phosphorus is the second most abundant element in the body, after calcium, and is mostly stored in bones and teeth. Phosphorus is also an important structural component in cells and makes up the backbone in DNA. Phosphorus plays a role in maintaining the appropriate acid/base balance in the body, regulating growth and cell differentiation, regulating energy utilization, and aids with protein synthesis, amino acid exchange, and transport of fatty acids in the body. Despite its importance, phosphorus deficiency is one of the most common deficiencies in livestock and poultry worldwide. Bulk feed ingredients, such as corn and soy, do have phosphorus in the form of phytic acid, or phytate. Phytate is considered a large anti-nutritional factor to monogastric animals due to their inability to produce intrinsic phytase. On the other hand, ruminants can produce endogenous phytases that break down phytate and absorb the available phosphorus. The amount of phosphorus found in corn and soy are not high enough to sustain the needed phosphorus for domesticated livestock and poultry, so supplemental phosphorus is added to diets.
Different Forms of Dietary Phosphorus
Supplemental phosphorus in livestock and poultry come in three forms; monocalcium phosphate, dicalcium phosphate, and mono-dicalcium phosphate. The three forms of supplemental phosphorus have a different chemical composition that may affect their bioavailability in the animal.
Monocalcium Phosphate
Monocalcium phosphate is comprised of one calcium ion and two dihydrogen phosphate ions, with the chemical formula of Ca(H2PO4)2. Monocalcium phosphate is considered a more soluble form of supplemental phosphorus as the release of phosphorus and calcium is quicker compared to dicalcium phosphate. Monocalcium phosphate is considered useful for immediate supplementation of phosphorus due to its quick release and can only exist in the anhydrous form. Digestibility of monocalcium phosphate ranges from 76-84% in poultry (Simon and van der Kliss, 1995) and 64% in swine (Damgaard Paulson, 1995). Monocalcium phosphate also provides a higher ratio of phosphorus to calcium.
Dicalcium Phosphate
Dicalcium phosphate is composed of two calcium ions and one phosphate ion, with the chemical formula of CaHPO4. Dicalcium phosphate can exist in both the anhydrous and dihydrate form, where two water molecules are added to the phosphate groups. Dicalcium phosphate is less soluble in water and thus has a slower release of both Ca and P relative to monocalcium phosphate. Dicalcium phosphate is considered more advantageous for long-term supplementation due to its slower release. Digestibility of dicalcium phosphate ranges about 77% in poultry (Simon and van der Kliss, 1995) and 59% in swine (Damgaard Paulson, 1995), Dicalcium phosphate provides a more equal ratio of calcium and phosphorus.
Mono-Dicalcium Phosphate
Mono-dicalcium phosphate is a co-crystallized compound of monocalcium phosphate and dicalcium phosphate. Mono-dicalcium phosphate has the chemical formula of Ca(H2PO4)2•H2O+CaHPO4•2H2O. Mono-dicalcium phosphate is produced by reacting calcium carbonate with defluorinated phosphoric acid at a ratio of 3:2. Mono-dicalcium phosphate has good solubility in water and has a bioavailability of 65-72% in swine (Damgaard Paulson, 1995) and 79% in poultry (Simon and van der Kliss, 1995). Mono-dicalcium phosphate granules have a longer retention time in the stomach compared to other forms, which allows for optimal absorption in the body, and has about a 1:1 ratio of calcium and phosphorus. Mono-dicalcium phosphate is one of the more common forms of supplemental phosphates and is the form of 21P.
Quality of Product
Processing Technique
Most supplemental phosphorus is mined from rock phosphates. These rock phosphates are then reacted with sulfuric acid to yield phosphoric acids and either calcium sulfate or calcium chloride, depending on the type of acid used to react with the rock sulfate. The phosphoric acid is filtered, purified, and defluorinated to get rid of excess fluorine and heavy metals. The defluorination step in producing phosphates is vital as fluorine toxicity symptoms can set in as soon as two hours after ingestion. Fluoride is naturally found in rock phosphates at concentrations up to 40,000 ppm. However, fluoride toxicity can occur at amounts as little as 20 ppm. Once the phosphoric acid has been properly filtered and defluorinated, it is reacted with a calcium source, often calcium carbonate, to form supplemental phosphates. The level of calcium the phosphoric acid is reacted with will determine if the phosphates will be a dicalcium or monocalcium phosphate.
Importance of Testing
Mined rock phosphates are often contaminated with heavy metals such as lead, cadmium, and arsenic. As previously mentioned, rock phosphates also contain an elevated level of fluorides. Testing every product is important, but testing phosphate sources becomes even more important when toxicity levels of unwanted contaminants are low and set in quick. Additionally, it is important to test products for active component levels to ensure accurate levels in formulation and specification of nutrients.
Pure Product
It is frequent practice to blend down concentrated feed ingredients to a more flexible level to allow for easier formulation. In the case of phosphorus, some higher concentrated products may be blended down to a 21% active component. However, the issue with blending down products such as phosphorus is that it may affect the absorption of nutrients due to higher concentrations of carrier. When using supplemental phosphorus, testing for phosphorus and calcium levels and ensuring product purity can ensure proper nutrient requirements are met for growth, development, and production.
Calcium to Phosphorus Ratio
Both calcium and phosphorus are essential minerals for skeletal development, growth, and efficient production. Calcium and phosphorus share an absorption pathway, and excess calcium can lead to a decrease in phosphorus digestibility. Calcium sources, mainly limestone, are very inexpensive so low-cost formulation software may add additional calcium to drive down diet costs. Appropriate calcium to phosphorus ratios are 4:1 in laying hens, 1.5:1 – 2:1 in broilers, 1:1 – 1.2:1 in swine, and 1.4:1 – 2:1 in dairy cows. Ensuring an appropriate calcium to phosphorus ratio will maximize absorption of both minerals and aid in animal production.
Phosphorus is an essential dietary mineral that aids in many bodily functions. There are various sources of supplemental phosphorus that have different bioavailability and chemical compositions, so it is important to recognize which source of supplemental phosphorus is going into animal diets to optimize development and performance. Additionally, testing for heavy metals and toxins and ensuring product purity is vital for appropriate phosphorus supplementation. Finally, it is also important to maintain and ensure appropriate calcium and phosphorus ratios for all livestock and poultry.