Phosphorus (P)

Phosphorus is an important mineral for animals and plants. Below, we discuss phosphorus in animal husbandry and in soil and crops.

Phosphorus in animals

About 80% of phosphorus (P) in the body is found in the bones. This phosphorus, as well as phosphorus in milk, occurs in the form of calcium phosphate (Ca₃(PO₄)₂. Thus, both phosphorus and calcium (Ca) are required for bone formation and milk production, with the ratio of the two minerals being important.

High-producing dairy cows require large amounts of phosphorus for milk production. A shortage can therefore occur easily. The usual rule of thumb is that 1kg of milk contains one gram of phosphorus, upon which additional requirements can be estimated. With the help of hormones, vitamin D regulates the absorption and resorption of calcium and phosphorus to and from the bones. The older the animal gets, the more difficult it becomes to mobilize calcium and phosphorus from the bones, thus increasing the risk of milk fever.

Phosphorus is also important for the functioning of the rumen, as it plays a role in the formation of microbial protein and the production of enzymes. The level of phosphorus in the blood is not stable; rather, it varies according to requirement, absorption from the intestine, and resorption from the bone. Phosphorus is also a component of the energy compound Adenosine triphosphate (ATP) and a part of phospholipids: an important part of cell membranes and the skin. In addition, phosphorus is found in the genetic material (DNA) of the animal.

Phosphorus deficiency
A phosphorus deficiency leads to reduced fertility, feed intake and milk production, as well as osteoporosis. In growing animals, this can lead to skeletal deformation and poor feed efficiency. 

Phosphorus surplus
A surplus of phosphorus surplus is unlikely, as cows can excrete excess absorbed phosphorus through saliva, urine and manure. An extremely high phosphorus level may cause diarrhoea.

An extremely high phosphorus level may cause diarrhoea. In addition, during dry periods, it may inhibit magnesium absorption and thus indirectly increase the risk of milk fever. The CVB (2005) indicates a toxicity limit for phosphorus of 10g/kg dry matter (for chronically high levels).

By performing the Ration Check from Eurofins Agro, you will find out the level of phosphorous in your mixed ration and you can immediately make adjustments if necessary.

In recent years, there has been a lot of attention on the environmental effects of phosphorus. This has resulted in rations for dairy cattle containing significantly lower levels of P, without any negative effects.

Phosphorus in soil and crop

Phosphate (P) in the soil is not always available to the plant. Several complex soil processes play a role in this. Calcium, iron, aluminum, soil texture, pH and organic matter all have an impact. Fertilisation and moisture supply during the growing season influence the phosphorus content in grass and silage. Adequate moisture in the soil causes phosphate to dissolve. In that form, the grass can absorb the nutrient. On average, a spring silage contains four grams of P per kilogram of dry matter. On plots where phosphorus extraction is structurally higher than the supply, a decline in the phosphate status of the soil – and subsequently also in the crop – can be expected over time. The

Fertilization Manager from Eurofins Agro provides insight into the state of the soil and gives advice on fertilisation.

Compound feed ingredients normally contain more phosphorus than roughage. The growth stage also affects the content: the older the crop, the lower the P content. Types of roughage with a relatively high phosphorus content include brewer grains, grasses and grass silage, while silage, straw (in a later growth stage than grass and grass silage) and potato products are again very low in phosphorus.