Phosphorus (P) - cattle

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 Requirements (CVB, 2016).
Category g/kg dry matter g/animal/day
Young cattle from 4 months 3.4 13
Young cattle from 9 months 2.3 13
Young cattle from 16 months 1.8 13
Dry 8-3 weeks to calving 1.9 21
Dry 3-0 weeks to calving 2.0 22
Lactating (20 kg) 2.5 47
Lactating (40 kg) 3.3 79

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. 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).

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.

Forage Manager

Ration Check