One of the biggest scourges in the lives of dairy farmers is milk fever. The disorder affects freshly calved cows, rendering them helpless and, if left untreated, or if treatment is not effective, the cow will die.

On top of this, it opens the door to a myriad of other disorders such as mastitis, ketosis and limb injury.

The good news is that it can be avoided, and even where it does occur, effective treatment should ensure a rapid recovery.

In my view, you can divide herds up into two cohorts. On the one hand are herds who experience milk fever very rarely i.e. it is being managed appropriately or the herd is at low risk.

The other cohort is of herds where the disease is much more prevalent, either because preventative measures are not being implemented correctly, or because the herd is at much higher risk of the disease.

So what is milk fever? Milk fever is a metabolic disorder caused by insufficient calcium in the bloodstream, causing the cow to get weak and, if left untreated, likely die.

Generally it is older, higher yielding and cows in too good body condition score that are at more risk. There is anecdotal evidence to say that Jersey and Jersey crossbred cows are more at risk too.


The main cause of milk fever is that cows aren’t able to mobilise enough calcium quickly enough after calving.

There are a number of predisposing factors, such as not enough magnesium before calving or high levels of potash in the silage.

Having too much calcium in the diet pre-calving can also make them lazy at mobilising calcium after calving.

One of the key prevention tools, aside from making sure BCS and potash levels aren’t too high in the silage, is to increase the amount of magnesium in the pre-calving diet.

Spreading sweetened cal-mag or magnesium flakes on the silage of the dry cows, in addition to their ordinary dry cow mineral will greatly increase their magnesium intakes.

Spreading 60g per cow per day of sweetened cal mag (33% magnesium) will supply an extra 20g of magnesium.

Magnesium flakes are generally lower in magnesium at 12%, so to get 20g of magnesium you would need to feed 170g of flakes on the silage or in the water.

Flakes tend to be less palatable than sweetened cal mag. Other options include giving a calcium bolus, a high calcium liquid feed or a bottle of calcium under the skin to freshly calved cows.

Cows that got milk fever in previous years are more likely to get it again, therefore these cows need extra special treatment.