Subclinical milk fever - the silent killer?

On average in the UK, subclinical milk fever is affecting up to 75% of the herd. It’s unrecognisable and generally remains untreated, as a consequence it's the gateway to other metabolic diseases and ultimately an early cull cow.

Subclinical milk fever - the silent killer?

Milk Fever

Clinical milk fever incidence is currently running close to the 10% mark in UK dairy herds. It's costing approximately £200 per cow, while subclinical milk fever can affect up to 75% of the herd, it’s unrecognisable and generally remains untreated.

Hypocalcaemia or milk fever in dairy cows can be defined as situations where the blood calcium concentration is below normal (normal plasma Ca being 2.1-2.8 mmol/l). Cows suffering from hypocalcaemia can be divided into 2 groups:

  • Clinical milk fever
    Dairy cows experience milk fever and display well know symptoms

  • Sub-clinical
    Dairy cows show no clinical signs of milk fever, however blood calcium concentrations drop below 2.0mmol/l and cows become highly susceptible to secondary conditions.

Milk fever – both clinical and subclinical, occurs at calving, which is probably the most stressful time of the cow’s life. She will be changing environment, diet and groups all at the same time as well as undergoing a massive physical challenge. Milk fever incidents also increase with the number of lactations.

That’s not all. Cows suffering from milk fever are between four and nine times more likely to suffer from a miscellany of other metabolic orders, many of which are related to each other. They each come with a significant price tag not only in treatment and vet costs, but also with losses from future milk and fertility delays. Cow suffering milk fever are likely to have increased risks:

  • 9-fold increase in the incidence of ketosis in cattle
  • 6 times more dystocia/ calving difficulties
  • 4-fold increase in the incidence of left displaced abomasum
  • 4 times more cases of retained placenta

Even a slight reduction from normal calcium levels can significantly impact production and profitability. A small decrease in blood calcium can increase the risk of:

  • Displaced abomasum
  • Lower milk production
  • Reduce reproductive performance
  • A negative energy balance

During the final six to eight weeks of pregnancy, most dry cow diets contain more calcium than is required, consequently the cow is only passively absorbing calcium. However, at calving there is a sudden demand for calcium for colostrum production and also for muscle contractions relating to calving and udder function, and the required level simply cannot be met by passive absorption. Active calcium absorption and mobilisation is required, yet it takes between 24 and 48 hours for her to change to active absorption, consequently there is always a drop in calcium levels around calving.

The consequences of low blood calcium, can be seen in the following diagram showing how it can be a gateway to other metabolic diseases and ultimately death. 


Intravenous calcium will give a quick response to a clinical case and often save a cow’s life, however it doesn’t reduce the problem; IV calcium, may cause fatal cardiac problems and perhaps most significantly, shut down the cow’s own ability to mobilise the calcium she requires at this critical time. Cows treated with IV calcium often suffer a hypocalcaemic relapse 12 to 18 hours later.

Subcutaneous and oral calcium supplementations can be given around calving but are often not given as required and there is only a small amount of absorption. Energy drenches can be used to provide a quick response to energy deficiency. Neither of these offer a preventative effect and both are poor for reducing subclinical hypocalcaemia/ milk fever.



Since both clinical and subclinical milk fever and consequential metabolic disorders are mainly related to the cow’s diet, the challenge is to maintain her feed intake and rumen balance around and shortly after calving. However, it is important to manage the cow carefully during the entire dry period to minimise fat deposition in the liver, maximise liver health and therefore also improve ovarian development for the next lactation and fertility cycle.

  1. Maintaining cow condition is critical 
    Target condition score 3 at drying off and calving to prevent fat being laid down inside the cow, especially in her liver otherwise it will reduce her ability to control her own mineral balances, in particular calcium. During the dry period, target feeding 9MJ/kg ME with a 12kg DM intake.
  2. Achieving the correct calcium balance around calving – X-Zelit
    X-Zelit is a calcium binding additive containing synthetic zeolite. This product binds calcium from the diet during the last two weeks prior to calving. The additive stimulates the cow’s hormonal system to actively absorb and mobilise calcium to ensure she is fully ‘fired up’ at the time of calving. Cows are subsequently more energetic, have higher feed intakes and are ‘ready to go’. Consequently they are less likely to fall in to energy deficit and also suffer fewer metabolic issues. This is a scientifically proven strategy, that has been working for farmers for over 10 years.
  1. Paying attention to detailed feed management
    Housed dry cows should be stocked at approximately 75% normal rate, ideally 10m2for the average Holstein cow and at least 80cm trough space should be provided per cow with food pushed up at least four times per day.


For further information on milk fever, clinical or subclinical or to find out more about X-Zelit. Please contact us on 015242 63139.


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