Agrifert - Liquid and Solid Fertilisers, Soil Conditioners and Animal Health Supplements

About Milk Fever

About Milk Fever

Recent work done in the United States indicates that anionic salts such as Magnesium Chloride and Magnesium Sulphate are more effective than neutral or cationic such as dusting with Magnesium Oxide.

No dietary supplement can completely eliminate milk fever, but may reduce incidences by as much as half. There are no guarantees, this is not an exact science, however, farmers have been reporting calmer herds, which is an indication that the Magnesium Sulphate programme has been very good.

A dairy cow requires 5 grams a day of elemental Magnesium, yet can store less than 2 grams, therefore supplemented Magnesium must be ingested every day.


200 cows ideally need the following supplementation:

200 cows x 5 grams = 1 Kg elemental Mg per day = 10 Kg magnesium sulphate heptahydrate (10%) per day.
Apply to a good length of grass 5-10 days before grazing.
Regular herbage testing through this period is strongly recommended,
R.J. Hill Laboratories have specific DCAD tests for milk fever likelihood
(DCAD or Dietary Cation-Anion Difference)

These tests are based on the Potassium levels in the soil in relationship to the Magnesium and Sodium levels.

  • The excessive use of Potassic Super and other harsh fertilisers has taken pasture Potash levels (above 3%) into the danger zone on many farms. The animal's requirement for Potassium is less than 1%. Potassium is a cation, and in excess, increases dietary alkalinity.
  • Magnesium Oxide (Causmag) is the traditional pasture preventative for Milk Fever, however, Magnesium Oxide does not improve the DIETARY CATION ANION DIFFERENCE (DCAD). It's a bit like trying to start your car with a battery that has 2 positives.
  • Magnesium Sulphate Heptahydrate is an "anionic salt". This will reduce the dietary cation anion difference(DCAD).
  • Magnesium Sulphate is the most palatable of the commonly used salts, but palatability is enhanced further if mixed with a palatable carrier and foilar fed onto pasture. Agrisol Winter-N is a seaweed based mineral rich neutral liquid fertiliser and is the ideal carrier for both Magnesium Sulphate and Magnesium Chelate. It is advisable not to drench Magnesium Sulphate.