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Mastitis and Milk Fever

What is Milk Fever?

Milk fever is the most important nutritional disorder affecting dairy cows. It is a macromineral disorder commonly affecting dairy cows around the time of calving, usually within 1-2 days of giving birth¹. One clinical case of milk fever leads to an 8 times increased risk of a case of mastitis.

Milk fever is the name given to the condition when cows show clinical signs of low blood calcium levels. At a subclinical level, these signs will not be seen, however blood calcium levels are still below normal (hypocalcaemia). 

Clinical Milk Fever

Cows show overt clinical signs, which may include: Cold extremities, a low temperature, mild bloat, poor appetite, constipation, unsteadiness on their feet or an inability to rise.

Signs can develop rapidly within 2-4 hours and, if untreated, can result in death of the cow within 10-24 hours, either as a direct result of the condition, or indirectly through related complications as “downers”².

Subclinical Milk Fever

Calcium levels are below “normal” but there are no apparent clinical signs; this may resolve or develop into clinical milk fever. Subclinical milk fever can have negative impacts on health and productivity¹.

Clinical cases can give an indication of a level of subclinical milk fever; for every clinical case there are around 3-6 subclinical cases in the herd⁴, however herds can also have a problem with subclinical milk fever without clinical cases.

Why does Milk Fever occur?

99% of calcium in the cow’s body is stored in the bones and teeth. The rest circulates in the blood and needs to be maintained with a narrow range⁵. With the onset of lactation there is a sudden and massive demand for calcium: an extra 80g per day².

The cow can adapt to this change by drawing on her own calcium reserves (bone and tissues), improving absorption from the diet and by reducing losses in the urine5,8. This adaptation occurs with the help of the cow’s calcium homeostatic mechanisms.

There is a balance between lactational calcium demands and the ability of a cow to mobilise her own calcium reserves. Imbalance in this may lead to clinical or sub-clinical milk fever.

What are the impacts of Milk Fever?

Clinical milk fever affects around 4-9% of UK dairy cows¹. Individual farms have clinical incidence rates of up to 60%². For every clinical case another 3-6 cows in the herd could be suffering from subclinical milk fever⁴. 

Every dairy cow is at risk of milk fever; most suffer from some degree of hypocalcaemia at calving⁵.

It is common for the odd case of clinical milk fever on a farm to not be perceived as a problem, and only when the number of cases suddenly increases is it considered a problem. However, every case of clinical or subclinical milk fever is a preventable problem.

Every case of Milk Fever has consequences. These include4,6:

  • Lowered immunity 
  • Slower rumen, abomasal and gut turn over
  • Reduced fertility
  • Reduction in milk yield

Increased risk of other early lactation conditions:


The estimated cost of a clinical case of milk fever is approximately £250⁸. On top of this, the consequences of subclinical milk fever may amount to as much as 1ppl on some farms¹⁰.

Which Cows Are At Risk?

All cows calving are at risk of milk fever, and most have some degree of low blood calcium (hypocalcaemia)⁵. However the risk does increase with age and parity4,5.

Risk factors that can indicate individual cows or herds at greater risk include:

  • Increasing lactations (any cow 2 lactations and above)2,4,5.
  • High yielding cows
  • Previous history of milk fever
  • Body condition score >3.5
  • Grass based diets / forage or diet high in potassium (K)/ high DCAD

Clinical and subclinical milk fever can, to a large extent, be prevented through transition cow dietary management and nutrition.

  • Plan dry cow forages in advance
  • Aim for lowest possible potassium in the diet of cows within 3 weeks of calving; this influences the incidence of milk fever
  • Minimise / eliminate application of dung – it is high in K (potassium)
  • Use straight nitrogen fertiliser on dry cow silage / grazing fields.
  • Later cuts are generally lower in potassium
  • Keep grazing tight – tops of stems have more potassium than the bottom
  • Calve cows down in the right body condition (BCS 2.75). Fat cows are more likely to get milk fever and have calving difficulties, ketosis etc
  • Ensure that there is a good magnesium supply to dry cows (involved in calcium absorption); this usually means either a mineralised dry cow roll or specific dry cow mineral
  • Feeding small amounts of certain salts such as magnesium or ammonium chloride can also help to reduce the risk – speak to your vet or nutritionist​

However there are frequently situations in herds or individual cows where there is an increased risk of milk fever:

  • Older cows
  • High yielding 
  • Previous case of milk fever in the cow/ herd

Supplementation with oral calcium such as Bovikalc® boluses helps to reduce the risk of milk fever.

Treating Clinical Milk Fever

Quick and effective therapy with intravenous calcium is essential to correct calcium levels, as this is a progressive condition that can lead to death in a very short period of time if left untreated.

Recurrence following treatment of a clinical case is common (30-35% of cases)⁹ and therefore measures to reduce the risk of milk fever following treatment are advisable, such as oral calcium supplementation.


For those groups or individual cows at risk of milk fever, oral calcium can be supplied prior to the risk period. Bovikalc® is an oral calcium supplement bolus containing calcium chloride and calcium sulphate. 

Each bolus provides 43g of available calcium:

  • Calcium chloride (fast release)
  • Calcium sulphate (slow release)

Each bolus has an acidifying effect, much like a DCAD diet, that helps the cow to mobilise her own calcium reserves⁴. The bolus dissolves in the rumen within 20-30 minutes and helps to raise blood calcium levels for a prolonged period of time.

How to Use Bovikalc®

For reduction of milk fever:

  • 1st bolus at the first sign of parturition 
  • 2nd bolus immediately after calving
  • If necessary give 1 or 2 additional boluses at 12-15 hour intervals.

For supplementation following calcium injection:

  • 1st bolus 2-3 hours after calcium injection
  • 2nd bolus 12-15 hours later
  • Provided that cows can raise their head and are starting to eat and drink

Only administer using the approved Bovikalc® applicator.

For more information please view our product page.


  1.  Husband (2005) In Practice 27, 88-92
  2. Bovine Medicine, Diseases and Husbandry of Cattle. 2nd Edition. Edited by A.H Andrews, R.W Blowey, H Boyd, R.G Eddy. Chapter 46 Major Metabolic Disorders. R.g Eddy. Pub: Blackwell Science Ltd
  3. Degaris, et al (2009) The Veterinary Journal 176, 58-69
  4. Houe et al (2001) Acta Vet Scanda 42, 1-29
  5. Sampson et al (2009) Veterinary Therapeutics 10 (3), 131-139
  6. Mulligan et al (2006) Irish Vet J. Vol 59 (12) 697-702
  7. Constable, P.D et al WBC, Chile 2010. Monitoring DCAD Diet in Dairy Cattle 
  8. Husband. Urine Monitoring – A New Tool To Prevent Milk Fever. Farm Business. 2011 11th Feb
  9. Thilsing-Hansen et al, (2002) Acta Vet Scanda 1-19
  10. Dairy Farmer, June 2011. Why Partial DCAB For Dry Cows Is Better Than None

An educational service from Boehringer Ingelheim Limited, Vetmedica Division, the makers of Metacam®, Bovikalc®, Ubrolexin®, Ubro Yellow®, Ubro Red® and Mamyzin®.

Advice on the use of Metacam, Bovikalc or other therapies should be sought from your veterinary surgeon. Metacam contains meloxicam, UK: POM-V IE: POM. Bovikalc contains calcium chloride and calcium sulphate and is not a veterinary medicine which is subject to authorisation by the Irish Medicines Board. Further information available from Boehringer Ingelheim Limited, Vetmedica Division, Bracknell, Berkshire, RG12 8YS, UK. Email: vetmedica.uk@boehringer-ingelheim.com | Web: www.boehringer-ingelheim.co.uk

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Date of preparation: Jul 2013. AHD 7729. Use Medicines Responsibly (www.noah.co.uk/responsible)