Milk fever
Also called Parturient paresis, hypocalcaemia
A sudden drop in blood calcium around calving. The cow becomes weak, trembles and then goes down, unable to rise. It needs urgent treatment.
Cause and spread
- Cause
- When lactation starts, calcium lost in the milk jumps from about 10 g to about 30 g a day, and some cows cannot raise their blood calcium quickly enough.
- How it spreads
- It is not infectious. It is most common in dairy cows, from calving to about 3 days into lactation.
Signs to watch for
- Restlessness, nervousness and trembling of muscles
- Unsteady walking, then lying down and unable to rise
- Cold ears and legs, with no fever
- Weak, flaccid paralysis and bloat in advanced cases
- Retained afterbirth, womb infection and other problems may follow
Many diseases look alike. Only a laboratory test can tell them apart, so please see a veterinarian for any sick animal.
How it is diagnosed
The diagnosis is based on the signs, the timing near calving and the response to calcium given by a veterinarian. A blood calcium test confirms low calcium and helps in follow-up and in herd checks; low phosphorus and magnesium may also be found.
- Usually the first testKetosis and Milk Fever Panel (BHB, Calcium, Glucose) (panel)Tests calcium with BHB and glucose after calving.
- Confirms the diseaseCalciumMeasures blood calcium.
- Supports the diagnosisPhosphorusLow phosphorus can occur with downer cows.
- Supports the diagnosisMagnesiumLow magnesium can add to weakness.
- Supports the diagnosisMetabolic Panel (Calcium, Phosphorus, Magnesium, Glucose) (panel)The key minerals and blood sugar together.
Prevention and control
- Feed dry cows a carefully balanced ration before calving, for example diets with a low or acidifying effect
- Avoid giving too much calcium before calving
- Watch cows closely in the first days after calving
- Treat a downer cow immediately: delay causes muscle and nerve damage
Where this information comes from
- Parturient Paresis in Cows · Merck Veterinary Manual
General information for animal owners and veterinarians, last checked October 2026. It does not replace the advice of your veterinarian, who should decide which tests and treatment your animal needs.