Hypomagnesaemia/ Grass Staggers

Grass staggers occurs when the level of magnesium (Mg) in the cerebrospinal fluid (CSF) falls below a critical level. 

Clinically the condition is characterised by hyper-excitability, muscular spasms (tetany) and convulsions. Hypomagnesaemia can be rapidly fatal. Outbreaks have been reported to occur where up to 20% - 30% of a cow herd can be found dead.
Grass staggers is caused by:

•  A deficiency in blood magnesium (Mg)
•  Generally affects adult lactating cows
•  Often the reason for sudden death close to calving

Magnesium is required by the cow each day, as Mg is not able to be stored and later mobilised. 
Essentially all New Zealand dairy cows should be supplemented with Magnesium from 3 weeks pre calving until well after peak lactation. Beef cattle may also require Magnesium supplementation.
Milk Fever (hypocalcaemia) is due to a shortfall of Calcium, typically within 48 hours of calving.  Low Magnesium levels in the blood upsets the cow's ability to mobilise and absorb more Calcium, and consequently a shortage of Magnesium is a key reason for the onset of milk fever.  
Rumetrace Magnesium capsules release Magnesium every day for 9 - 12 weeks.  They are typically used in older beef breeding cows where Magnesium supplements such as dusting Mg oxide onto pasture is impractical, and also prior to calving in 'springer' dairy cows.