Correct mineral nutrition is critical to cow performance, both in terms of improving milk output and reducing the incidence of many common health disorders.
And according to Dr Derek McIlmoyle, AB Vista’s EMEA Ruminant Technical Director, the impact on profitability can be significant.
He says: “The challenge is that minerals are often poorly absorbed and utilised by the cow, so simply feeding more is not always the best way to achieve the desired result.
“There are also numerous interactions that occur between minerals within the cow, and increasing the supply of one can create an imbalance that is as detrimental as not feeding enough.”
Taking calcium and magnesium as examples, the focus for most milk producers is on optimising supply during transition and early lactation, as well as at turnout for magnesium. However, both are critical for a range of metabolic functions.
Dr McIlmoyle says: “Hypocalcaemia post-calving is often referred to as a ‘gateway disease’, leading to a wide range of other issues. These include retained foetal membranes, ketosis, mastitis, displaced abomasums and metritis.
“What is less often discussed is the negative impact on muscle tone, which not only results in more calving difficulties, but also affects rumen function and dry matter intake.”
Research carried out at the University of Georgia highlighted the potential for improved calcium availability to increase dry matter intake (DMI) during early lactation.
The increase in calcium supply was achieved by replacing a sodium bicarbonate buffer with a high bioavailable calcium-based rumen conditioner, with any gain in DMI likely due to an increase in muscle tone which improved rumen contractions and faecal passage.
The net result was an improvement in milk production efficiency (5 per cent) and milk constituents.
"Demand for calcium rises massively at calving, from around 40–50g/day to 80–120g/day during early lactation,” explains Dr McIlmoyle.
“Forages high in potassium – such as grass silage – exaggerate the problem as potassium reduces the capacity for calcium release from bone reserves.”
Research has also shown the influence that magnesium has over calcium availability, stimulating the parathyroid hormone pathway that controls calcium mobilisation and absorption. However, for maximum effect, the magnesium needs to be soluble in the rumen.
“This interrelationship is why magnesium is so important during the transition period, helping limit the incidence of hypocalcaemia by improving calcium release from bone deposits,” Dr McIlmoyle adds.
“There is little magnesium available from internal reserves, so the cow is heavily reliant on the magnesium in the ration.
“What is needed is a ration that not only contains enough available magnesium to meet requirements, but also promotes good rumen function to maximise magnesium absorption.”
The bioavailability of the magnesium source used is also critical in meeting requirements. When improved by using different mineral sources, it has been shown the amount of mineral supplement required can be reduced by half. The result is greater overall efficiency, and more ‘space’ in the diet that allows cow energy requirements to be met using less expensive feeds, such as cereals.
Dr McIlmoyle says: “The most effective source of magnesium for ruminant rations is magnesium oxide, which contains around 55 per cent magnesium. This is much higher than in magnesium chloride or magnesium sulphate, which are also used in mineral supplements.”