Milk Fever Prevention in Dairy Cows: A Welfare Priority

Milk Fever (Hypocalcaemia) in Dairy Cows

Milk fever, or periparturient hypocalcaemia, is one of the most significant metabolic diseases affecting dairy cows. It occurs when blood calcium levels drop precipitously at calving — driven by the sudden onset of colostrum and milk production, which demands enormous quantities of calcium that the cow cannot mobilise fast enough. Clinical milk fever affects approximately 5–7% of dairy cows in the UK each year, while subclinical hypocalcaemia (no overt signs) affects an estimated 25–50% of multiparous cows.

Animal Welfare Impact

Milk fever causes significant suffering and is a key welfare concern:

Clinical milk fever: Progressive muscle weakness, inability to stand, recumbency, and — without treatment — death within 12–48 hours
Subclinical hypocalcaemia: Reduced feed intake, impaired immune function, increased susceptibility to metritis, mastitis, displaced abomasum, and ketosis
Secondary welfare effects: Downer cow syndrome (inability to rise after successful calcium treatment) causes prolonged recumbency pain and distress

Cows that experience milk fever are 2–3 times more likely to be culled within the same lactation.

Risk Factors

Parity (3rd lactation and beyond carry highest risk)
High milk yield potential and Holstein breed
Dry cow ration high in calcium and/or potassium
Obesity at calving (BCS >3.5)
Selenium or vitamin D deficiency
Previous history of milk fever

Prevention Strategies

Dietary Cation-Anion Difference (DCAD)

Manipulating the DCAD of the dry cow ration is the most evidence-based approach to prevention. Feeding a low or negative DCAD diet (using anionic salts such as calcium chloride, magnesium sulphate, or ammonium chloride) in the close-up dry period (last 3 weeks) acidifies the blood slightly, activating parathyroid hormone receptors and priming calcium mobilisation.

Target urine pH: 6.0–6.8 (Holsteins), confirming effective acidification. Monitor pH at 3-day intervals.

Oral Calcium Supplementation at Calving

Providing oral calcium boluses at calving and 12 hours post-calving is effective for at-risk cows (3rd lactation and above, previous history). Products include calcium chloride gels and propylene glycol/calcium combinations. Avoid overdose — calcium chloride can cause tissue irritation if administered incorrectly.

Pre-Calving Vitamin D and Magnesium

Adequate magnesium is essential for PTH responsiveness. Target blood magnesium of 0.9–1.1 mmol/L pre-calving. Supplementation via ration magnesium (0.4% DM) or magnesium boluses is recommended for herds with grass-based systems where magnesium availability may be limiting.

Dry Cow Management

Avoid high-calcium dry cow diets (<20g Ca/day in far-off dry period)
Maintain BCS at 2.75–3.25 at dry-off
Provide adequate vitamin D3 supplementation (minimum 30,000 IU/day)
Minimise potassium in close-up rations (avoid high-K forages)

Treatment When Prevention Fails

Intravenous calcium borogluconate (400ml of 40% solution, administered slowly over 10–15 minutes) remains the primary treatment. Key welfare points:

Treat promptly — recumbent cows deteriorate rapidly
Monitor heart rate during IV administration (risk of cardiac arrhythmia)
Follow up with subcutaneous calcium to prevent relapse
Assist recumbent cows with rolling, padding, and nursing care
Recumbent cows unable to rise after 24 hours require specialist veterinary assessment

Herd-Level Monitoring

Target: <2% clinical milk fever incidence in mature cows. A higher rate indicates inadequate prevention and represents a significant welfare deficit requiring immediate dietary review.