Dairy NZ

Magnesium Supplementation

Supplementing with magnesium (Mg) for two to three weeks pre-calving will reduce the risk of milk fever.

It can be difficult to supply enough Mg when using magnesium sulphate (MgSO4; Epsom Salts) or magnesium chloride (MgCl₂). Therefore dust pastures with magnesium oxide (e.g. CausMag) as well.

Dry cow Mg requirements are 0.35% diet – this equates to the following quantities of supplement MG per day per cow:

Down the throat Mg per cow:

• Jersey 12g
• Crossbred 16g
• Friesian 20g.

Magnesium Concentrations

• Mag Oxide (Caus Mag)² 50-55%
• Mag Chloride (MgCl2) 11%
• Mag Sulphate (MgSO4; Epsom salts) 9%

Note²: Allow for 50% wastage dusting MagOxide

For example, one way to achieve required dietary Mg concentration is 60g per cow of MgCl₂ or MgSO₄ added to the water trough and 50-70 grams Mag Oxide per cow dusted on pastures.

• For more information refer DairyNZ Farmfact Magnesium Supplementation (3-1).