Magnesium

All cows are deficient in Magnesium, to some extent, during late pregnancy and early lactation. High producing cows are more deficient. Cold, wet weather in spring depresses grass growth and cow intakes.

Magnesium is required for the production of hormones that are important for the absorption of calcium from the gut mobilisation from bones.

In most situations, 15gm of magnesium per cow per day from 3 weeks before calving should be adequate. Magnesium chloride and magnesium sulphate can be added to the water, but each is only about 10% magnesium (150g needed to provide 15g of magnesium), and too often can affect the palatability of water and therefore the intake.

Commonly this is achieved by adding 60 grams of Magnesium chloride or Magnesium sulphate into the water trough and dusting pastures with 50 to 70 grams of Magnesium oxide per cow per day as well. Magnesium is absorbed predominantly from the rumen.

Phosphorous

The most obvious use for Phosphorus is bone production but it is also used for proteins, nucleic acids, lipids and other processes. While 80-85% of phosphorous is found within the bone, the rest is found within body tissue and fluids.

Consequences of deficiencies are well documented. The initial effect is a fall in blood plasma levels, followed by withdrawal of calcium and phosphorus from the skeleton. Loss of appetite can occur leading to poor feed conversion efficiency and a lowered live weight gain.

The amount needed depends on the animals feed, more being required with phosphorous deficient feeds such as fodder beet.

Calcium

Calcium metabolism at calving is one of the most important animal health factors influencing production, reproduction and feed conversion efficiency. While 98% of the calcium in the body is present in bone and teeth, the remaining calcium in the body is essential for life - muscle activity, blood clotting, nerve transmission and the dynamics of enzyme function.

Just prior to calving the foetus has its greatest demands and milk production is commencing, both with increased demands for calcium. The calving process requires a large muscular effort needing calcium and energy.

Around calving and early lactation the average dairy cow has about 10g of calcium readily available, but needs 4 – 10 times that to function fully and maintain a healthy ongoing metabolic state.