A cow’s transition period, where they shift from late pregnancy to lactation, spans three weeks prior to calving to three weeks post calving. This is a crucial time to set the cow up for her whole lactation. Successful transition includes ensuring dairy cows reach their targeted body condition score, are metabolically fit (liver), milking cow fit (rumen and forging ability) and supplemented with appropriate levels of magnesium, calcium and phosphorus.

Milk Fever (clinical hypocalcaemia)

Milk fever is a metabolic disorder where a cow’s blood calcium levels drop dangerously low. This can occur at any stage of lactation but usually occurs within 24 to 72 hours after calving. If the cow is unable to mobilise enough calcium quickly from the gut and the skeleton to meet the demands of the udder making colostrum and milk the blood calcium concentration decreases resulting in sub-clinical (very common) or clinical hypocalcaemia (milk fever). Most cows are low in calcium immediately after calving.

Initial symptoms of milk fever include loss of appetite, muscle tremors, grinding teeth and ataxia. Advanced stage symptoms can include extended or flaccid neck (S-bend), going down, dry nose, cold ears, reduced rumen contractions and an increased heart rate. The cow will die if left untreated.

Calcium Balance

The calcium concentration of milk is relatively constant (1.2g / litre), the more milk that is produced the higher the demand for calcium. There are only 2-3 grams of calcium in the blood and the remainder must come from the gut or the skeleton. In early lactation, cows mobilise considerable calcium from their skeleton and this must be replenished in late lactation.

Considerable amounts of calcium are secreted into colostrum and milk. A high producing cow turns over her blood calcium very 4-6 hours, so it is important to ensure an adequate calcium intake for lactating cows.

Dietary Cation- Anion Difference (DCAD)

In dairy farming, DCAD refers to the balance of positively charged cations (sodium & potassium), and negatively charged anions, (chloride and sulphur), expressed as milliequivalents per kilogram of dry matter (meq/Kg DM).  In dairy cows, the DCAD manages the acid- base balance to optimise calcium metabolism.

For transition cows approaching calving a low DCAD diet aims to slightly acidify the cow to improve calcium mobilisation and reduce the risk of milk fever.  By feeding a negative DCAD diet pre-calving, the cow’s blood pH drops slightly, which forces her natural systems to start pulling calcium from her bones and absorbing it efficiently from her gut.

Most New Zealand pastures have high DCAD (up to 850 meq/Kg DM) due to high potassium concentrations which negatively influences the mobilisation of calcium. Limiting application of potassium fertilisers on to pastures prior to calving is recommended.

Recommended Calcium Supplementation

A cow’s calcium requirements increase the moment she calves and begins producing colostrum.  The objective of supplementation should be to prime a cow’s calcium metabolism pre -calving and ensure all cows are adequately supplemented with calcium and magnesium immediately after calving. Avoid low levels of magnesium in the blood as it causes grass staggers (hypomagnesaemia), low milk yields and reduction in absorption of some trace minerals. All cows should receive magnesium pre-calving. The amounts vary based on existing rations and history of supplementation.

In a high producing cow, the demands for calcium are high and diets that do not contain the recommended 0.8-1% of dry matter intake need to be supplemented. New Zealand pastures vary in calcium concentration from 0.1 – 1.0 %, depending on location, soil type, season, fertilizer history. As a guide, most pastures calcium concentration is less than 0.6%. 

All cows should receive additional calcium during the lactation, especially over the colostrum period. It takes 3 to 4 days for the skeletal calcium supply to become available. The importance of calcium is underrated especially for immune function, energy balance and disease recovery. 

Options for Calcium Supplementation

Lime Flour or calcium carbonate contains 34-39% calcium and is the product of choice for lactating dairy cows. As a rule, it should not be used pre-calving unless under the guidance of a qualified rural professional.

The usual dose for Lime Four is 60-300gms per cow per day in feed. If dusting on pasture always allow for 50% losses.

Gypsum or Calcium Sulphate contains approximately 23% calcium and can be used both pre-calving (as it has a negative DCAD) or after calving.

As a guide, to provide 40g of Calcium/cow/day; 174grams of Calcium Sulphate (Gypsum) is required. It may also be dusted on pasture but again allow for 50% wastage.

Consult your vet

Due to the complex metabolic processes in cows, it is recommended a farmer consults a vet or rural professional for guidance, based on recent blood tests rations fed and history, on the use and application of calcium sulphate (Gypsum) as a nutritional supplement either side of calving.

References

Original article written by Dr Tim Jenkins for Winstone Gypsum.

Dairy NZ : Transition cows - DairyNZ | DairyNZ

Thank you to Byran McKay, Dairy Production Systems Ltd, for reviewing and updating this article in June 2026.