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• Don't Forget the Macros

Don't Forget the Macros

Macro minerals are probably the most under rated feed additive in terms of value for money.

Many producers spend thousands of dollars each year on ensuring their cows have adequate vitamin and trace element supplementation and neglect to provide the necessary macro minerals to ensure full metabolic efficiency during both the lactation and dry period.

A macro mineral is an inorganic element that is essential for normal function of the animal.
It is called a macro mineral because it is required in gram quantities per day by the cow.

The elements referred to as micro minerals or trace elements are required in milligram or microgram amounts.  That is one thousandth or one millionth of the macro mineral amount.

The macro minerals are calcium, phosphorous, sodium, chlorine, potassium, magnesium and sulphur.  These minerals are supplemented to a greater or lesser extent in most well formulated rations.  Usually calcium, sodium, chlorine and magnesium can be added relatively cheaply.  Phosphorous, potassium and sulphur are usually not supplemented but can be if required.

Calcium

• Calcium is the most significant element for the dairy cow.  It is excreted in huge quantities in milk during lactation.  Despite this many herds do not get any supplementation to replace the calcium being lost every day.  So where does the calcium come from that is being excreted if it doesn't come from the diet?  The only place is from bones.  Calcium is removed from bones to keep blood levels up in early lactation.  This will occur regardless of how much calcium is offered to the cow during this time.  As she gets further into her lactation, her ability to absorb calcium from the gut increases and she is able to take in greater amounts than those being excreted in milk.  The process of removal of calcium from bones is similar to that seen in post-menopausal human females referred to as osteoporosis.
  This lactational osteoporosis seen in dairy cows is a natural phenomenon.  Our use of anionic salts in the transition period is designed to stimulate this process during the transition period.  This enables cows to provide adequate calcium to meet requirements when lactation starts.
  Supplementation with calcium should occur during the entire lactation.  In early lactation it is required to assist with immediate requirements.  In late lactation it is required to replenish stores that are drained during early lactation.  Supplementation is usually achieved with the use of ground limestone.  This is cheap and easy to source.  Different brands of limestone will have different solubility in water.  This has an affect on the availability of the calcium.  Other sources of calcium are available.  The most common used in this district is DiCalcium Phosphate (DCP).  DCP has less total calcium by weight than lime but is far more soluble.  This makes it more available to the cow and can make it more palatable.  As a result more calcium can be absorbed.  DCP is a far more expensive option than lime but has been used in cases of mid lactation hypocalcaemia outbreaks to good effect.
  As a general recommendation cows should receive 50-100 grams of lime per cow per day through their entire lactation to ensure adequate calcium is available for present and future use.

   

Magnesium

• It will be a surprise to many that some herds are still not supplemented with magnesium.  The main stimulus for this article was our experience with a couple of herds that appear to have responded quite dramatically to magnesium supplementation.
  
  Magnesium cannot be stored by the cow for future use in the same manner as she does with calcium.  They need to have a source of magnesium every day.  This is more an issue when herds are grazing pasture.  This is the basis behind the name for clinical hypomagnesaemia, Grass Tetany.  Whilst the cases of grass tetany seen these days are low there is still a magnesium deficiency occurring in most herds that are unsupplemented.  This will show up as a higher incidence of other metabolic diseases such as milk fever or acetonaemia or just as a poor production problem.
  
  Magnesium supplementation is cheap and simple.  Mag Ox should be fed at 30 grams per cow per day.  A lot of farmers stop feeding it during late spring.  It is advisable to continue feeding it throughout the year to be safe.  If nothing else, the advantage of having a chemical of a pH of 8 going into the rumen at the same time as grain will help to combat lactic acid build up due to our slug feeding of grain in the dairy.

   

• Sodium and Chlorine are discussed together purely because they are usually supplemented together in the form of Sodium Chloride (salt).  Sodium is essential for all cell function and has many roles in the body.  It is excreted in large amounts in the milk.  It acts to enable the movement of most nutrients into cells in tissue.  If sodium is deficient these functions are impaired.  This includes absorption of other macro minerals such as calcium and magnesium.  In high producing dairy cows the diet will almost always be deficient in sodium.  The level of deficiency depends on the feeds being fed and the other minerals such as potassium and chlorine.  Excess intake of sodium can eventually cause problems but levels have to be much higher than those given in this district.
  
  As a general rule supplementation with 50 grams of salt per day will be required.  Sodium bicarbonate supplies a significant amount of sodium.  If Bicarb is replaced with Eskalin for acidosis control, salt supplementation will become more necessary to make up for the drop in sodium levels.
  

• Macro minerals are essential for adequate milk production through the entire lactation.
• Supplementation with the major macro minerals is relatively cheap.
• It is better to feed a bit more of these minerals than not enough as they are safe.
• If herd production levels are less than is expected, macro mineral levels should be investigated