It is very important to give cows mineral supplements during the dry period and to start in time, to ensure that early calvers get their fair share.

Minerals will help to reduce the risk of calving problems, will enhance the quality of the colostrum and thereby reduce the risk of calf health problems, and prepare cows for lactation. The developing calf needs minerals, particularly iodine and selenium, to prevent the birth of weak calves that can die shortly after birth.

Colostrum is a very important source of minerals and vitamins for the calf’s immune system, deficiency will increase the risk of scour, navel-joint ill, and pneumonia.

During lactation the cow’s mineral levels can run quite low, hence the necessity to build levels up during the dry period. There are two groups of minerals: macro minerals (zinc, calcium, phosphorous, magnesium and potassium) and trace elements (copper, zinc, manganese, iodine, selenium and cobalt).

Methods of supplementation range from blocks to boluses, and powder form. Blocks are expensive and can lead to irregular intake, also some cows develop a liking for them while others get little or none.

Boluses are expensive, but one has the assurance that once all cows have been treated each will have received their proper share. However,they do not contain any vitamins.

The cheapest way to feed minerals is a powder pre-calving mineral, about 30g per day scattered over the silage, preferably twice each day. This should go on for at least eight weeks, preferably longer.

There are many commercially available pre-calving mineral mixes. Be sure you get one containing all the trace elements and with vitamin supplementation. The cheapest may not always be suitable.

Some farms may have very specific requirements, for instance where there is a high level of molybdenum or iron in the soil and herbage can interfere with uptake of selenium and copper.

In such cases, one may have to get a specially prepared formulation in consultation with your vet or nutritionist.

Guidelines for macro element inclusion in dry-cow diets % on a dry matter basis, minimum levels:

  • Calcium minimum 0.45% – always have the level of calcium in the diet higher than phosphorous.
  • Phosphorus 0.2% – ideally under 0.35%.
  • Sodium 0.4%.
  • Magnesium 0.3% – increase to 0.4% where there is a history of problems or where dietary potash is high.
  • Potassium – once level is >1.4%, risk of clinical and sub clinical milk fever increases.

    • Suggested vitamins per head per day:

  • Vitamin A 30,000iu to 50,000iu – for immune system.
  • Vitamin D3 – 8,000iu to 10,000iu – calcium metabolism.
  • Vitamin E 150mg to 500mg – for immune system.
  • Vitamin B12 25 to 50 micrograms – for digestion.