Pre-calving mineral requirements

A successful transition can be achieved by getting the management and nutrition of dry cows right. This successful transition revolves around four key pillars: 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 for between six to eight weeks. This is to ensure that a good reserve of minerals is built up to allow the cow to calve down without any issues and continue into the lactation to follow.

Silage testing

It is important to note that the mineral status of Irish soils and forages varies tremendously from farm to farm and year to year, and most Irish forages do not supply the required amount of minerals to get a cow through the dry period. The simplest and most accurate way of knowing mineral status is testing the forages, whether they be grass, grass silage, maize or whole crop silage. This will give a good indication of the mineral status and help you ensure that your cows are getting 100 per cent of the minerals they need.
To date, many of this year’s silage analyses are showing a deficiency in phosphorus, selenium and manganese. There is also an excess supply of potassium, due to a high level of soluble nitrogen caused by high fertiliser and slurry application rates along with aluminium and molybdenum.

Macrominerals

Magnesium is needed for the metabolism and absorption of calcium within the cow around calving. Throughout the dry period, a cow requires approximately 45g magnesium/day, depending on body weight. If a silage mineral analysis is 0.15 per cent magnesium, a cow eating 11kg dry matter intake (DMI) during the dry period will take in 16.5g silage. As a result, the mineral supplement will need to supply at least 28.5g of magnesium. If the feed rate of the mineral is 120g/head/day, it needs to be a minimum of 24 per cent magnesium to make up the deficit.

Potassium in Irish silages is typically between 1.8-2.4 per cent. However, the dry-cow requirement is only 0.52 per cent. Potassium interacts closely with magnesium, tying it up in the rumen, which can slow down the absorption and mobilisation of calcium, leading to milk fever. With sufficient magnesium supplementation, the typical levels of potassium can be managed. If potassium is greater than 1.8 per cent in silage, it can be managed with magnesium by introducing Cal-Mag or sweetened Cal-Mag. Levels above 1.8 per cent need further measures as prescribed by a nutritionist.

Milk fever

Research has shown that, even where milk fever is relatively well controlled, approximately 33 per cent of cows may experience sub-clinical milk fever. I often get the following question from customers: ‘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 potassium is higher than 1.5 per cent and magnesium is less than 0.4 per cent of DMI (40g/head/day), the dry cow is at risk of milk fever or subclinical milk fever. The level of magnesium supplementation is very important; a dry cow will need around 40g+ in total. Potassium locks up magnesium, and magnesium is needed to help mobilise calcium from the bones.
• Check the calcium level in the dry-cow diet. If it is greater than 0.45 per cent of total DMI (~50g), the cow will become too dependent on the supplemented calcium. This may result in her not being able to mobilise calcium from her bones, which can lead to milk fever.
• Dry off cows between BCS 3-3.25, and maintain this BCS throughout the dry period. The risk of milk fever is reduced if cow BCS is monitored and controlled in late lactation and 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

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

• Zinc supplementation is important at all times of the year, as it helps to keep somatic cell counts under control and maintain hoof hardness.
• Selenium is a natural antioxidant and maintains the immune systems of calves and dairy cows. Selenium 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.
• Copper plays an important role in fertility. Copper deficiency can cause many issues, such as poor growth, reproduction problems, impaired immunity and diarrhoea.

Another common question on farms relates to 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:

• First, as always, test your forage for minerals. Choose a mineral based on your forage mineral analysis. High potassium and low magnesium may also be the issue here, so you may need a mineral with higher levels of magnesium.
• 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 (e.g., zinc oxide), feeding high levels of them can cause mineral interactions. For instance, zinc oxide may interact with copper and make it less available for absorption, which may lead to more cows with retained placentas.
• Choose a mineral such as Bioplex copper, manganese and zinc and Sel-Plex organic selenium. These are proven to mimic the minerals found in grass and are therefore 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 chelated form – as in Bioplex and Sel-Plex minerals – lead 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. Many farmers across Ireland are now seeing a positive response in their herds by using these products in their dry cow mineral. Make your dry cow mineral count by using these proven technologies as part of a dry-cow nutrition programme that generates greater return on investment, benefitting both cow performance and farm profitability.