The initial symptoms of magnesium deficiency are nervousness, ears pricked, nostrils flaring, eyes alert and head held high. Movement is stiff, like walking on stilts, and cows stagger when forced to move quickly. Cows suffer loss of appetite and reduced milk production. Death results from a "Tetany" where the muscles contract uncontrollably including the heart.

Magnesium and grass staggers

Magnesium plays an important role in grass staggers prevention.

Magnesium requirements are also affected by the levels of potash and calcium in the diet. Some farms with very high potash levels in pasture will require high rates of magnesium supplementation.

Applying potassium fertiliser or lime within three months of calving can affect cow magnesium levels at calving. Where magnesium is added to water and dosage is not accurate there is a risk of the water becoming toxic and stock refusing to drink.

For more information refer to:

• DairyNZ Farmfact: Magnesium supplementation (3-1)
• DairyNZ Farmfact: Ryegrass staggers - management options (3-8)

Dietary magnesium concentrations and quantity of supplementary magnesium required (g/cow/day)

Quantities of magnesium sources to supply the required amounts of pure magnesium (down the throat)

If dusting CausMag on pasture, need to at least double, possibly triple, the above to allow for field losses. When mixing with feed, double the rates above.

Amount of CausMag dusted (g/cow/day)