Milk Fever


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Calcium Magnesium Checklist to mitigate milk fever

Milk fever is a metabolic disorder in dairy cows caused by insufficient calcium, often seen after calving. It can cause lowered milk production and other health issues, like ketosis and metritis. Keeping blood calcium levels low before calving and ensuring calcium in the diet after calving can help manage this condition. In addition, magnesium plays a crucial role in preventing milk fever and should be included in the cow's diet. It's important to monitor your cows and apply the right dietary practices to prevent this disorder. This page provides valuable insights and a helpful checklist for managing milk fever.

Milk fever is a metabolic disorder caused by insufficient calcium, commonly occurring around calving.

Milk fever, or hypocalcaemia, is when the dairy cow has lowered levels of blood calcium. Milk fever generally occurs within the first 24 hours post-calving, but can still occur two to three days post-calving. It can be either clinical or subclinical.

  • Clinical milk fever includes both 'downer' and 'non-downer' cows with less than 1.4mmol/L blood calcium.
  • Sub-clinical milk fever includes cows with less than 2.0mmol/L but more than 1.4mmol/L blood calcium.

Milk fever increases the risk of other metabolic diseases and infections, such as ketosis and metritis, and approximately 5 percent of downer cows do not recover.

In 2000, a New Zealand study indicated that cows suffering from clinical milk fever produced 14 percent less milk, while cows with sub-clinical milk fever produced 7 percent less milk. The impact of this disorder on the average dairy farm was estimated to be $8,000 per 100 cows.

The dairy cow obtains calcium from her diet or from stores in her bones. Although there are substantial amounts of calcium available from these sources, the absorption from the intestines, or resorption from bone, is under tight hormonal control and is affected by other minerals (e.g. phosphorus and magnesium) and vitamins (e.g. vitamin D).

With the onset of lactation, and production of colostrum, the cow’s requirement for calcium increases substantially (400 percent increase in a day). To meet these calcium requirements, the cow must increase both the absorption and resorption processes. Any factors that interfere with these processes mean the cow cannot meet the increased demand for calcium, and this results in lowered blood calcium concentration and milk fever.

There are many factors that influence milk fever, including nutritional and management factors, as well as others outside of the famer’s control, such as the weather.

For more information on all of these factors see:


It is recommended to maintain low blood calcium levels before calving to stimulate an increase in the proportion of calcium that is absorbed from the diet during the pre-calving period.

Once she has calved, a cow’s calcium requirements increase by around 400 percent to support colostrum production. All cows should receive dietary calcium during the colostrum period. This is commonly administered through dusting of pastures, or by incorporating it into supplements being fed. Cows require at least 100g of lime flour per cow per day, with this level increasing to 300g for cows with an increased risk of milk fever.

Remember, when dusting minerals in the paddock, the levels need to be either double or triple to allow for losses.

After the colostrum period there is no known benefit of supplementing cows with calcium unless milk fever is occurring in the milking herd, or cows are consuming large amounts of low calcium feed, such as maize or cereal grains.


Magnesium plays a vital role in the prevention of milk fever. It is essential for the efficient absorption and resorption of calcium. Supplementation with magnesium has the largest effect on decreasing the incidence of milk fever.

Supplementing with magnesium for two to three weeks pre-calving will reduce the risk of milk fever. However it does not build up a store of magnesium, and continued supplementation will be required during early lactation.

For more information on the levels required, and methods of administration of magnesium, see the grass staggers page.

Checklist to mitigate milk fever

Technote and section
✔ Ensure cows are at target BCS 2-3 weeks prior to calving 12
✔ Separate at-risk cows prior to calving and feed appropriately 12
✔ Supplement all cows with magnesium pre and post-calving 13.3
✔ Keep dietary calcium levels low pre-calving 13.4
✔ Supplement all colostrum cows with calcium 13.5

✔ Avoid feeds high in phosphorus (e.g. PKE) and supplement 
with phosphorus if diets are low in phosphorus (e.g. fodder beet)

✔ Avoid grazing effluent paddocks 13.7
✔ Understand the impact of DCAD in your system 13.8
Last updated: Sep 2023
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