MCP, MDCP, DCP: three phosphates, three uses

Three products carry phosphorus into compound feed and mineral feed: monocalcium phosphate (MCP), monodicalcium phosphate (MDCP) and dicalcium phosphate (DCP). All three come out of the same chain, phosphoric acid and calcium, but they are not formulated, priced or bought the same way.

Three salts, three contents

MCP, Ca(H₂PO₄)₂, carries 21 to 22.7 % phosphorus depending on the producer, with about 16 % calcium. It is the most concentrated and the most water-soluble of the three. MDCP is a blend of MCP and DCP, around 21 % phosphorus, sold as MCP in some countries and as MDCP in others. DCP, CaHPO₄, carries 17 to 18 % phosphorus and about 24 % calcium; it exists as a dihydrate and as an anhydrous form, which do not behave alike in the animal.

A common convention classifies as MCP a product with more than 80 % monocalcium phosphate, and as DCP a product with at least 51 % dicalcium phosphate. Everything in between is called MDCP, and the label says little about actual performance.

Content is not digestibility

What matters to the animal is digestible phosphorus, not total phosphorus. Two laboratory criteria approximate it: solubility in water and solubility in 2 % citric acid. A good MCP is almost entirely water-soluble; a dihydrate DCP dissolves well in citric acid; an anhydrous DCP, less so. Some products labelled MDCP at 21 % phosphorus, highly soluble, behave like a slightly weak MCP; some MCPs at 22 % perform below what their content promises.

The difference comes from upstream: the rock and the acid. Igneous rock, as in Finland or Russia, is low in cadmium and heavy metals but high in fluorine; sedimentary rock, as in North Africa or the United States, needs deeper purification. The purity of the phosphoric acid used, rarely stated, weighs as much as the process.

Why DCP dominates in Italy, France and Spain

Formulation habits were set thirty or forty years ago, around local plants and the processes available. DCP took hold in southern Europe, made from rock and hydrochloric acid, or from phosphoric acid and lime, with a high calcium content that suits maize-and-soy diets. MCP took hold in the north, in premixes and mineral feeds, and among manufacturers who buy phosphorus by the kilogram of phosphorus.

As a result, at equal phosphorus prices the same European plants sell two different products to two different markets, and import flows, Chinese ones in particular, can only be read by separating the two grades.

What bone DCP changes

Dicalcium phosphate of animal origin, a co-product of gelatine and bone processing, is allowed in the European Union for non-ruminant animals and banned for ruminants under the TSE regulation. Its digestibility is measured like that of a mineral DCP; its price follows gelatine more than phosphoric acid. For a poultry or pig buyer it is a phosphorus source that escapes the acid contract, provided the origin is traced and the labelling rules are met.

What to ask a supplier

• total phosphorus, water-soluble and citric-acid-soluble phosphorus;
• calcium, fluorine, cadmium, arsenic and lead, with the analytical methods;
• the origin of the rock and of the acid, and the process (phosphoric or hydrochloric acid);
• particle size and flowability, for dosing in premixes;
• a digestibility measured on the target species, not just a data sheet.

The right price of a feed phosphate is compared per kilogram of phosphorus delivered to the plant, not per tonne. Digestibility is judged afterwards, product by product, with table values and a safety margin: the nutritionist decides, not the label.