Historically, gout was called a rich man’s disease because it mostly affected people who consumed high quantities of wine, red meat and other rich foods, at a time when rich foods were scarce. I’m reminded of this when looking at the risk factors for milk fever:

  • Cows in too good body condition score.
  • Cows being fed good-quality silage that is high in potash.
  • Older cows in fourth lactation onwards.
  • There seems to be an annual increase in the percentage of cows succumbing to milk fever, with vets and farmers alike reporting a big increase in cases. The classic sign of milk fever is a cow that won’t get up, is slow to get up, is listless and weak. They can often be seen lying down with a slight twist in their neck.

    The primary treatment is to give affected cows calcium

    If left untreated, milk fever can be and often is fatal. Early treatment is critical for a successful outcome. The primary treatment is to give affected cows calcium. A near immediate response in the animal is observed when liquid calcium is given into the bloodstream through a vein. Giving affected cows liquid calcium under the skin takes much longer for the calcium to be absorbed, so administering the calcium into the vein is advised for downer cows.

    The cause of milk fever is a severe lack of calcium and the highest risk period is in the 24 hours after calving, although cases can occur up to five days after calving. The freshly calved cow draws down a significant quantity of calcium from bone reserves for milk production. It is when the cow is unable to draw down enough calcium that milk fever occurs. Indeed, not fully milking out freshly calved and high-risk cows is one control mechanism for milk fever.


    There are a number of complicating factors when it comes to milk fever. High calcium diets prior to calving can lead to an increase in milk fever post-calving. This is because the cow can get “lazy” at mobilising calcium reserves from the bone. This tends to be more of an issue with autumn-calving cows that can be at grass, which is high in calcium.

    However, feeding extra calcium in the few days prior to calving can be part of an effective control measure.

    Magnesium is an important element in the control of milk fever. Magnesium can regulate the absorption of calcium, so feeding extra magnesium prior to calving can help to increase the amount of calcium available to the cow.

    Silage for dry pregnant cows should be no more than 2% potash

    There is a big link between magnesium and potassium, with high potash diets locking up magnesium and preventing the mobilisation of calcium. Lush grass tends to be high in potash and fields that were heavily fertilised with potash prior to cutting for silage can lead to high potash levels in the silage.

    Silage for dry pregnant cows should be no more than 2% potash. This can be checked with a silage mineral analysis. Some farmers will feed specifically low potash silage to dry cows to reduce potash levels in the diet.

    Feeding additional magnesium where potash in the silage is high will help to overcome this issue.

    There are a couple of options here such as adding magnesium to the water of dry cows or sprinkling magnesium flakes or Cal Mag on to the silage in addition to the dry cow mineral.

    Other ways of preventing milk fever include giving cows additional calcium shortly before and after calving

    In general, dry cow minerals provide insufficient magnesium for cows close to calving and being fed high potash silage.

    Some farmers feed between 40g and 50g of magnesium per day in the run up to calving. Most dry cow minerals fed at 100g/day will only provide 24g/day.

    Other ways of preventing milk fever include giving cows additional calcium shortly before and after calving. This can come in the form of liquid feeds, bolus or subcutaneous injection.

    Milk fever tends to be a gateway illness for other health issues such as mastitis, retained cleanings and infertility.

    Managing body condition score in dry cows and keeping a close eye on the potash levels in the feed for dry cows will help to prevent the illness.

    In short

  • Milk fever is common in older cows in too good body condition score.
  • Milk fever is more prevalent where silage is good quality and high in potash.
  • Feeding higher levels of magnesium prior to calving will help to mobilise more calcium after calving.
  • Cows with milk fever are more at risk of other diseases.