Mineral supplementation pre Calving

Precalver mineral supplementation prior to calving is essential to ensure a healthy cow and new born calf. Minerals in silage can vary and as a result it is important that precalver minerals are fed 6-8 weeks prior to calving. Bag minerals are one of the most effective methods of supplying minerals. Normal feeding rates are 100g/head/day. Therefore if feeding 100 dry cows you will need 10kg per day so over an 8-week dry period you will need 560kg of minerals.

When choosing a precalver mineral it is important to check the feeding rate and the quantity of vitamins and minerals in the bag. The important macro minerals are Magnesium, Calcium and Phosphorous. These are the minerals whose interactions will be involved in most metabolic issues at calving. The microminerals Copper, Selenium, Iodine, Cobalt, Manganese, Zinc and Vitamins A, D3 and E are also essential. These are needed in smaller quantities and are primarily involved in cow and calf health, immunity and reproductive performance.

Calving is a very stressful period for the cow and can challenge the immune system and lower the ability to fight off infection. You can boost the cow’s immune system by using a good precalver mineral leading to lower levels of metritis, mastitis, SCC and lameness. Mineral supplementation during the dry period is also important for the new-born calf. Calves rely on the placental transfer of trace minerals from their mother to meet the requirements for foetal growth and trace mineral status of the cow affects colostrum quality which is important for the new born calf’s  immunity and health.

Calcium, Magnesium, Potassium

Calcium supply is the biggest challenge the cow faces at calving. Cows obtain calcium from their diet or from their bones. Although there are substantial amounts of calcium available from these sources, the absorption from the intestines or resorption from bone is under tight hormonal control and is affected by phosphorus, magnesium and vitamin D. With the onset of lactation, and production of colostrum, the cow’s requirement for calcium increases by 400% in a day. To meet these requirements, the cow increases both the absorption and resorption processes. Any factors that interfere with these mean the cows cannot meet the increased demand for calcium and resulting in lower blood calcium concentrations and milk fever.

Milk fever (hypocalcaemia) arises when the cow has lower levels of blood calcium. Milk fever generally occurs within the first 24-hours post-calving but can occur 2-3 days post-calving. Cows become restless and disorientated. They may stagger or be weak on their legs. In severe cases, the cows will be unable to stand and be unresponsive. Cows with milk fever are more prone to other metabolic issues (retained foetal membrane, metritis, dystocia, displaced abomasum, mastitis). Cows suffering from clinical and subclinical milk fever produce less milk over the following lactation. Milk fever has a large impact on herd health, production and profitability.

Magnesium plays a vital role in the prevention of milk fever. Supplementation with magnesium has the largest effect on decreasing the incidence of milk fever. It is essential for the efficient absorption and resorption of calcium. Precalver minerals should contain high levels of magnesium as it is critical in the activation of vitamin D3. The precalver should also contain Vitamin D3 to help with the absorption of calcium.


A cow with a deficiency of trace minerals and vitamins in late pregnancy can compromise the immune system of the calf. This may increase susceptibility to scour, pneumonia, navel ill, joint-ill, etc.

Selenium, Vitamin E, Vitamin A, Vitamin D

Selenium and Vitamin E are often considered together as they have a similar function. Selenium crosses the placenta from the cow to the calf and so selenium supplementation of pregnant cows has been shown to increase the reserves in new born calves. Deficiency can result in stillbirths, or the birth of weak calves that are unable to suck unaided. Vitamin E doesn’t cross the placenta from the cow to the calf. As a result the calf is born with a low levels of vitamin E and is highly dependent on an adequate intake of colostrum.

Like Vitamin E, Vitamins A and D do not cross the placenta in significant amounts and so the calf relies upon ingestion of colostrum for these. Vitamin A plays an important role in combating infection and it increases disease resistance and stimulates the immune system. Cows that have a deficiency of vitamin A can also produce dead, weak or blind calves because vitamin A is needed for growth of the foetus.


Iodine is an essential trace element for growth, development and reproduction. Low dietary iodine intake during pregnancy has been associated with an increased incidence of small and weak calves, increased incidence of goitre, decreased resistance to hypothermia, decreased survival and low immunity.

Rhyno Mills Range of Precalver minerals

This winter Rhyno Mills have a large range of high spec precalver minerals with excellent vitamin and protected mineral levels. For more information on our mineral specs or to order your minerals please call your local Rhyno sales representative for further information.

The importance of the dry cow mineral cannot be overemphasised and supplementation for 6-8 weeks over the dry period is a small price to pay to ensure that there are no problems at a very busy time of the year.