Pre-calving mineral requirements: Make your dry cow mineral count

By Eddie Phelan, regional manager, Alltech Ireland

Successful transition from the dry period into lactation is one of the most crucial moments in a dairy cow’s lactation. It will have a direct impact on milk production, cow health and reproductive performance during the subsequent lactation.

A successful transition can be achieved by getting the management and nutrition of dry cows right. This successful transition revolves around four key pillars: body condition; nutrition; minerals; and management.

During the dry cow period, these four pillars will prepare farmers for easy, stress-free calving and set their herds up for successful lactation by reducing metabolic issues around calving, including milk fever, retained placenta, displaced abomasum and ketosis. As previously mentioned, one of the four pillars is getting mineral nutrition correct in the dry period.

Dry cows should be fed a dry cow mineral for the duration of the dry period: Ideally, between weeks six to eight. This is to ensure there is a good reserve of minerals built up to allow the cow to calve down without any issues and continue into the lactation to follow.

Silage testing

Most Irish silages do not supply the required amount of minerals to get the cow through the dry period. As a result, these minerals need to be supplemented. If you have not already done so, test your silage for minerals. This will give a good indication of the mineral status and ensure you are feeding a balanced mineral supplement.

It is important to note that the mineral status of our soils and forages varies tremendously from farm to farm and year to year. The simplest and most accurate way of knowing the mineral status is testing the forages being fed to cows, whether it be grass, grass silage, maize or wholecrop silage. Once known, informed decisions can be made on the most effective way of supplementation.

To date, many of this year’s silage analyses are showing a deficiency in phosphorus (P) and an excess supply of potassium (K) due to a high level of soluble nitrogen (N) caused by high fertiliser and slurry application rates.


Magnesium (Mg) is needed for the metabolism and absorption of calcium (Ca) within the cow around calving. Throughout the dry period, a cow needs 40g+ of Mg/day.

If a silage mineral analysis is 0.15% Mg, a cow eating 11kg dry matter intake (DMI) during the dry period will take in 1.65g from silage.

As a result, the mineral supplement will need to supply at least 35–40g of Mg. If the feed rate of the mineral is 120g/head/day, it needs to be a minimum of 25% Mg to make up the deficit.

K in Irish silages is typically between 1.8–2.4%. However, the dry cow requirement is only 0.52%. K interacts closely with Mg, tying it up in the rumen, which can slow down the absorption and mobilisation of Ca, leading to milk fever.

With sufficient Mg supplementation, the typical levels of K can be managed. If K is greater than 1.8% in silage, it can be managed with Mg by introducing Cal-Mag or sweetened Cal-Mag. Levels above 1.8% need further measures as prescribed by a nutritionist.

Milk fever

Research has shown that, where milk fever is relatively well-controlled, approximately 33% of cows may experience sub-clinical milk fever.

While dealing with customers, I often get the question: I had a higher number of cows go down with milk fever before calving, despite using boluses for some. What can I do to reduce the risk of this happening again?

We recommend the following:

  • Test dry cow silage for minerals: If K is higher than 1.5% and Mg less than 0.4% of DMI (40g/head/day), the dry cow is at risk of milk fever or sub-clinical milk fever. The level of Mg supplementation is very important; a dry cow will need around 40g+ of Mg in total. K locks up Mg and Mg is needed to help mobilise Ca from the bones;
  • Check the Ca level in the dry cow diet: If greater than 0.45% of total DMI (~50g), the cow will become too dependent on the supplemented Ca. This may result in her not being able to mobilise Ca from her bones, which can lead to milk fever;
  • The risk of milk fever is reduced if cow body condition score (BCS) is monitored and controlled in late lactation and throughout the dry period. Cows should be dried off between BCS 3–3.25, and this BCS should be maintained throughout the dry period. Cows with both too high and too low BCS are shown to have an increased risk of milk fever.

Importance of trace minerals during the dry period

Trace minerals, or micro minerals, play a huge role in the overall immunity, fertility and production of dairy cows. Irish grass silages have been shown to be 63% low in copper (Cu), 69% low in selenium (Se) and 29% low in zinc (Zn) (Rogers and Murphy, 2000). As a result, supplementation is essential.

Important trace minerals:

  • Zn supplementation is important at all times of the year as it helps to keep somatic cell counts (SCC) under control, reduce incidences of mastitis and maintain the hardness of the hoof;
  • Se is a natural antioxidant and boosts the immunity of calves and dairy cows by playing a role in the resistance to viral and bacterial infection. Se supplements will only be effective if fed with the correct levels of vitamin E, as the two work in synergy. This is very important on maize and silage diets, where vitamin E is very low;
  • Cu plays an important role in fertility and immunity. Cu deficiency can cause many issues, such as poor growth, reproduction problems, impaired immunity and diarrhoea.

Another common question on farms relates to the level of held cleanings. When the level of held cleanings increases on-farm, the level of mineral supplementation also tends to increase, but this may not always be beneficial.

See below some key points on the issue:

  • First, as always, test your forage for minerals. Choose a mineral based on your forage mineral analysis. High K and low Mg may also be the issue here, so you may need a mineral with higher levels of Mg;
  • Then, check the label to see what type of mineral you were feeding; ask your supplier if you are not sure. If most of the elements are inorganic (i.e., zinc oxide), feeding high levels of inorganic minerals can cause mineral interactions, such as the zinc oxide interacting with Cu, making it less available for absorption, which may lead to more cows with retained placentas;
  • Choose a mineral that contains organic minerals, such as Bioplex® Copper, manganese (Mn), Zn and Sel-Plex® (organic selenium). These are proven to mimic the minerals found in grass and, therefore, are more bioavailable with better absorption and less chance of mineral interactions.

Minerals that go to work, not to waste

Research has shown that feeding these trace minerals in their organic form — Bioplex Copper and Zn and Sel-Plex, an organic form of Se — leads to better absorption, storage and utilisation by the cow. This builds up the cow’s immune system and lowers the risk factors associated with difficult calvings and retained placenta.

Make your dry cow mineral count by using proven technologies as part of a dry cow nutrition programme that generates greater return on investment, benefitting both cow performance and farm profitability. Many farmers across Ireland are now seeing a positive response in their herds by using Bioplex and Sel-Plex in their dry cow mineral.

Further information

Make your dry cow minerals count, find out more about Bioplex and Sel-plex by clicking here