The mineral muddle

Mineral deficiencies are frequently blamed as a cause of poor production and reproduction within dairy herds and many who drive up the tanker track will claim to have the "silver bullet" that will fix the problem. Usually, this will be a "special recipe" including a secret ingredient that will enhance the effect of the minerals contained in their brew.

Calcium (Ca) and magnesium (Mg) are known as macro-minerals and a gross deficiency can lead to milk fever and grass staggers respectively. However, these conditions are just the tip of the iceberg as a sub-clinical deficiency of these minerals will lead to a whole range of less obvious consequences that will affect the farm's profitability. Balance of these minerals is usually achieved through the strategic use of Mg oxide, Mg chloride, Mg sulphate and possibly gypsum, through the transition period followed by the administration of lime flour and Mg oxide through the early lactation period. Dosing to the nearest 10grams per cow per day should be accurate enough but remember that "more is NOT usually better" in this situation.

On the other hand, the micro- or trace minerals are only required by cattle in much smaller levels. These are primarily copper (Cu), cobalt (Co) and selenium (Se), although iodine, manganese and chromium are also often mentioned. Because of the requirement for only "trace" amounts of these minerals, dosing needs to be very accurate so as to avoid the toxic effects while ensuring that the desired response is achieved.

Most New Zealand soils are deficient in these trace minerals but local variations are common. These variations are then exaggerated by:

  • The season - where higher rainfall leads to greater leaching but also to higher pasture growth rates which will dilute the concentration of the element in plant tissue. More rain will also increase the quantity of soil ingested while grazing, which will affect the quantities of minerals available to absorb.
  • Management practices - which can result in lower grazing residuals, which will restrict intakes and so reduce the mineral intake.
  • Farming intensity - which will determine the quantity of brought-in supplement feed, in particular, palm kernel, which has a high copper content.
  • Fertiliser policy - which will vary between farms, such as the application of lime changing the availability of minerals.
  • Interactions between minerals that compete for uptake or form complexes that make them unavailable for absorption.

There is no doubt it is crucial for the micro-mineral status of your herd to be adequate to support high production, excellent fertility, a robust immune system, and growth rates in young stock that ensure them reaching target live weights. Regular blood and liver sampling of dairy stock are therefore recommended to ensure that this is the case. Pasture sampling coupled with soil test results can assist with the diagnosis of trace element issues and can help decide on the best treatment plan.

The moral of the story - minerals are complicated and silver bullets are usually expensive and over-rated, so seek good advice before parting with your hard earned money!


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