From talking to vets and knackery workers, milk fever continues to be a big problem this spring and a major cause of mortality.

Some farms are more affected than others, either due to cows being in too-high body condition score prior to calving, high potash levels in the silage, too much calcium in the diet pre-calving, not enough calcium in the diet post-calving or not enough magnesium in the pre-calving diet.

It is said that for every clinical case of milk fever there are numerous other undiagnosed sub-clinical cases that are likely to affect mastitis incidence and fertility.

A clinical case where the cow is down presents other risks such as that cow getting an injury when trying to get up or getting mastitis such as e-coli mastitis.

Treating milk fever is a lot of extra work and stress and something every farmer can do without at this time of year.


Feeding higher levels of magnesium pre-calving primes the cow for metabolising calcium after calving and overcomes some of the issues with high potash in the silage.

Spreading sweetened cal-mag or magnesium flakes on the silage of the dry cows within two weeks of calving, 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 but if spread on the silage the cows will eat them. Some farmers mix the flakes with some meal to make them more palatable.

Magnesium can also be added to the water either through a dosing system or by manually adding magnesium flakes.

Other options include giving a calcium bolus, a high calcium liquid feed or a bottle of calcium under the skin to freshly calved cows but these solutions tend to be more expensive and time consuming than feeding extra magnesium.

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