Magnesium (Mg) - cattle

Magnesium (Mg) is an important mineral for cattle, and most of it is found in the bones. However, unlike calcium (Ca) and phosphorus (P), it cannot be easily released from the bones, especially as the animal ages. Because a dairy cow needs relatively large amounts of magnesium, magnesium deficiency is commonplace.

Magnesium plays a role in muscle contractions and the transmission of nerve impulses. It is also important for various metabolic processes, particularly through the activation of enzymes. Another important function of magnesium is its involvement in the production of parathyroid hormone (PTH) by the parathyroid gland, which affects calcium metabolism. Magnesium levels in the blood are less stable than calcium. A deficiency can be detected through urinalysis.

Magnesium Requirements (CVB, 2016).
Category g/kg dry matter g/animal/day
Young cattle from 4 months 1.7 6.7
Young cattle from 9 months 1.8 10
Young cattle from 16 months 1.9 14
Dry 8-3 weeks to calving 1.9 22
Dry 3-0 weeks to calving 2.1 23
Lactating (20 kg) 2.1 38
Lactating (40 kg) 2.4 56


Magnesium deficiency 

A magnesium deficiency can occur when magnesium absorption is reduced; for example, as a result of high (unstable) protein and potassium contents in the ration. Magnesium deficiency is also regularly observed in young cattle, especially during the grazing period. A deficiency leads to reduced feed intake, a stiff gait, and head disease. In addition, a deficiency during a dry-off period increases the risk of milk fever, especially in combination with a calcium deficiency. However, this only happens when magnesium in the blood drops sharply. 

Because magnesium plays a role in muscle contractions and impulse transmission in the nerves, nervous behavior, uncontrolled movements and increased sensitivity to stimuli are observed with prolonged magnesium deficiency. Muscle tremors and cramps can also occur and eventually even paralysis and death.

Magnesium excess 

Magnesium excess does not occur easily, as animals can excrete excess magnesium through the urine. An extreme excess, however, can lead to decreased muscle tone and diarrhea. The CVB (2005) indicates a toxicity limit for magnesium of 6 g/kg dry matter (for chronically high levels).

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