Milk Fever (or Hypocalcemia) is a shortfall in the amount of calcium in the blood available to the cow.

It Occurs:

At or near the time of calving. The two lowest points of calcium availability for the cow are 12-hours pre- and 12-hours post-calving.

It can also occur in whole-herd ‘runs’ at grass, where there have been flushes of potassium-rich grass (usually in spring or autumn), or in sileage from secondary cuts from after such flushes.


The onset of milk production resulting in the sudden requirement for colostrum and milk. This causes levels of calcium in the blood to drop rapidly

  • A dry cow needs to absorb(1)23 g of calcium daily; this increases to over 40g in the milking cow(2)
  • Colostrum requires 2.5 g calcium per litre, milk requires 1.2 g calcium per litre.
  • If the cow is unable to mobilise enough calcium quickly enough from either her bone reserves or absorb sufficient amounts from her diet to maintain these levels of calcium in the blood, milk fever can occur.
  • In order to efficiently maximise the calcium absorbed from her diet and mobilised from bones, she needs to be in a state of mild metabolic acidosis.


Stage 1: Wobbly and trembling muscles. Possible loss of appetite

Stage 2: Down

It can also be linked to a reduction in smooth muscle function, which can be extremely painful.

Importance of Calcium in the cow:

[1] The efficiency of absorption of calcium from the diet increases from ~33% in the dry cow to ~48 % in the milking cow.

[2] Based on a cow producing 25 litres of milk, requiring 1.2 g calcium per litre of milk produced.

How do cows mobilise calcium?

A cow has to have her system in a mild metabolic acidosis to be efficient at both mobilising calcium and increasing absorption – when she isn’t efficient at mobilising calcium it can be that her system is too alkaline, so giving the right type of calcium is very important to help her system to achieve peak absorption when she needs it, as well as the correct amount of calcium to support her needs too.

Supplementation is therefore required if this mobilisation process does not happen quick enough to meet the cow’s demands for colostrum / milk production.

Injectable Calcium vs. Calcium Bolus

If a cow has gone down with milk fever, she should always be given injectable calcium to get her back up on her feet. DO NOT give a downer cow a calcium bolus until she is back on her feet, as her swallowing reflex can be impaired. She can then be given an Essential Calcium bolus to give a longer supply of the right forms of calcium to aid her recovery.

ESSENTIAL CALCIUM is a fast-acting sustained release calcium bolus for adult dairy cows over 400 kg, ideally given pre and post calving. In herds where there are known calcium problems, whole-herd application should be used to reduce the risk of milk fever throughout the herd.

Composition of each 203 g bolus, and how they work:

  • Reduces the risk of milk fever in dairy cows.
  • Provides a large supply of calcium within 50 minutes of administration and for up to 24 hours after.
  • Provides more calcium than the average daily requirement of a cow.(3)
  • Provides the right forms of calcium to support her own calcium mobilisation and utilisation.
  • Can be given to all cattle either just prior to or after calving as blanket herd support.
  • Neutral taste, aiding administration process.


Pre and Post Calving:

Administer one bolus at first signs of calving.

Administer a second bolus 12-24 hours after the 1st bolus if necessary.

Post Calving:

Administer one bolus immediately after calving.

Administer a second bolus 12-24 hours after the 1st bolus if necessary.

Remember: Can be used on the whole herd to help support cows to mobilise calcium as efficiently as possible.

For Further information and advice please contact us.

(3) The amount of calcium required changes as milk yield increases and decreases throughout the lactation period, on average a cow needs 40+g of calcium a day.