Why calcium balance matters
Around calving, a cow’s calcium needs triple to produce colostrum and milk. If her body cannot mobilise calcium fast enough, she may suffer from milk fever (clinical hypocalcaemia) or hidden low calcium (subclinical hypocalcaemia). Both can cause loss of appetite, weaker muscles, and higher risk of disease, leading to reduced fertility and milk yield.
With direct costs quoted at over £130 rising to greater than £400 when the impact on fertility, production and likelihood of cull is considered, it's worth investing in every possible measure to reduce risk. As sub-clinical hypocalcaemia is probably more frequent and its main cost is on the ‘expensive’ indirect impact on disease, productivity, and culling, it arguably has an even greater financial impact.
What happens when calcium drops?
Calcium controls muscle movement and immunity. Low calcium weakens rumen and uterine contractions, causing displaced abomasum, retained placenta, and higher risk of mastitis and metritis. Cows eat less, making them prone to ketosis and fatty liver, especially if they are fat or stressed before calving. Calcium is also vital for the function of the white blood cells involved in immunity and response to infection.
Which cows are most at risk?
- Older cows (3rd lactation and beyond)
- Over-conditioned (BCS >3.5)
- Cows under stress (heat, regrouping, overcrowding)
- Herds feeding high-potassium forages (lush grass, slurry-heavy silage)
- Cows with inconsistent or low feed intake before calving
Practical prevention
- Feed and forage management
- Use low-potassium forages (maize silage, straw, mature grass) in close-up rations.
- Include X-Zelit (a calcium-binding mineral product) in the final 14–21 days before calving where diet risk factors cannot be altered e.g. grass or silage rations. It works by temporarily blocking calcium absorption, triggering the cow’s own calcium mobilisation before calving. X-Zelit can be a strong complement to partial DCAD diets, especially where forage potassium levels make full DCAD feeding difficult.
- Feed anionic salts to adjust the dietary cation-anion difference (DCAD). This helps the cow’s metabolism prepare for calcium mobilisation.
- Partial DCAD diets aim for a safe, smaller drop in blood pH to reduce risk from high potassium diets. They utilise the inclusion of anionic salts such as Ammonium or Magnesium Chloride at lower, safe levels.
- Full DCAD diets use more anionic salts, targeting urine pH around 6.0–6.5, and are best for high-risk herds or high-forage potassium diets.
- Where full DCAD diets are implemented, it is essential to monitor urine pH weekly to ensure cows are responding properly, this is the only reliable way to confirm success.
- Ensure magnesium supply of 0.40–0.45% of DM (about 30–40 g/day).
- Keep rations consistent, well-mixed and palatable.
- At calving
- Give oral calcium boluses to older or high-risk cows at calving and again 12–24 hours later.
- Use calcium chloride products for fast absorption.
- After calving
- Keep feed available at all times and push up frequently.
- Avoid stress. Limit pen changes, rough handling, or competition.
- Monitor fresh cows for appetite, temperature, and signs of disease. Other helpful steps
- Avoid excessive phosphorus before calving, it can worsen low calcium.
- Manage heat stress with fans or sprinklers.
- Support immunity with vitamin E and selenium.
- Maintain good hygiene to reduce inflammation and infection risk.
Monitoring the herd
These can be useful alongside assessment of environmental and physical risk factors (feed space, water provision, BCS, stress etc)
- Blood calcium: Test at 0–1 and 4 days in milk (DIM). Aim herd mean ≥2.0–2.2 mmol/L. Lower 4-day levels may indicate inflammatory triggers.
- Urine pH: Check weekly to confirm correct DCAD response. Partial DCAD diets should average 6.5–7.0; full DCAD should be closer to 6.0–6.5.
- Key targets:
- Milk fever <2% of calvings.
- Retained placenta <8%
- Displaced abomasum <3%
- Ketosis <15%
Quick treatment guide
If a cow is recumbent, Calcium will often be given slowly IV, under veterinary guidance, then followed up with oral calcium once she can swallow. Always provide water, feed, and comfortable bedding. Always discuss use of Intravenous calcium with your vet, as it will potentially have a negative effect on Calcium metabolism once the initial rapid increase in blood Calcium level has dissipated.
Take-home message
Preventing milk fever means more than giving calcium, it’s about a robust, informed feed plan, managing stress, and keeping cows eating steadily. Choose the prevention system that suits your herd: X-Zelit-based programs, partial DCAD or full DCAD. Work with your vet and nutritionist, together, to monitor urine pH, ration minerals, and cow response. A steady transition means healthier cows, fewer problems, and more milk in the tank.