Magnesium calcium and energy

As with most things, prevention of metabolic disease is better than 'cure'.

Here are some key points:

Supplementing with magnesium will reduce the risk of milk fever and grass staggers (grass tetany)
Supplement with magnesium daily for two to three weeks pre-calving until after spring pasture growth rates have slowed (around December)
It can be difficult to supply cows with enough magnesium just through the water supply
Combine magnesium through the water supply with magnesium dusted daily onto pasture or silage
Dietary requirements of magnesium will vary due to cow liveweight (dependent on breed) as shown in Table 2 (Refer to DairyNZ FarmFact Magnesium supplementation 3-1 for dose rates of magnesium from different sources to meet daily requirements)
After calving, provide 150g/cow/day ground limestone (lime flour) daily during the colostrum period- double this rate if dusting; can also consider calcium-enriched molasses
Ensure the metabolisable energy (ME) requirement of grazing transition cows is met during the last month pre-calving (Equivalent to approx. 20% of a cow's empty liveweight (LW without the calf))
Consider using starter drenches on high risk cows at calving - 7+ year olds, or very fat, or with a history of metabolic problems.

Table 2. Dietary magnesium requirements and supplementation recommendations