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Supplementing with phosphorus in the green for improved breeder productivity

The key nutrients required by ruminants are water, metabolisable energy, protein, phosphorus, sulphur, sodium, calcium, vitamins, and trace minerals. The order in which these nutrients are listed is respective to their relative importance to the ruminant.

In the dry, the two most limiting nutrients are energy and protein. This is why we recommend that supplements high in protein are fed during this time. The higher the protein in the diet; the more efficient digestion will be, and as a result more energy will be available to the animal.

In the wet, energy and protein are high in green grass and generally do not need to be provided through supplements. Therefore, with an abundance of energy and protein in the diet, phosphorus then becomes the most limiting nutrient which can affect the overall performance of the animal.

So which animals require phosphorus the most and what are the effects of a phosphorus deficiency?

  • Young calves and lambs have the highest requirement for phosphorus to support their growth,
  • First calf heifers also require phosphorus for growth, pregnancy and lactation,
  • Breeders (ewes and cows) in their pregnancy term require phosphorus for the growing foetus and for lactation.

Livestock deficient in phosphorus will have a reduced daily dry matter intake which will greatly decrease productivity.

Deficiencies can result in poor appetite and low feed intake, poor growth, high breeder mortality, reduced fertility and milk production, bone breakage and in severe cases, bone deformities. There is also an increased risk of botulism when animals chew bones in their craving for the mineral. This does not mean however, that if your livestock aren't chewing bones then they won't be suffering from a phosphorus deficiency. Chewing bones is a sign that they are suffering from a severe deficiency and have been lacking the mineral for an extended period of time.

Lactating breeders have a very high requirement for phosphorus as they require it for quality milk production. If they do not have access to sufficient phosphorus to meet their milk production requirements, cows will begin to mobilise the mineral from their bone reserves in order to produce more milk for the calf. This means that the calf may be receiving milk of a poor quality that could affect their growth and the cows?۪ bone density and general health will begin to deteriorate as well.

What are the effects of phosphorus mobilisation from the bones?

Phosphorus mobilised from bone reserves during late pregnancy and lactation will have to be replaced at some stage during the annual cycle if the cow is to have adequate body phosphorus reserves for the subsequent pregnancy and lactation. This may not be possible for cows grazing low phosphorus pastures and producing calves every 12 months. Breeders producing calves every 18 to 24 months will have a greater opportunity to replenish phosphorus body reserves without supplementation. However, this is at the expense of herd productivity and profitability.

How can phosphorus supplementation in the green improve breeder productivity?

The table below shows data published by Meat & Livestock Australia (2012) on the benefits of feeding phosphorus supplements to cattle grazing native pasture on phosphorus-deficient soils in northern Australia.



Acutely deficient



Typical soil Phosphorus




Likely weight response to phosphorus supplementation by growing cattle (kg/year)

Native pasture




Likely response to phosphorus supplementation by breeder cattle grazing native pastures

Increased weaning rate (%)




Increase in calf weight at weaning (kg)






As you can see, growing cattle grazing on acutely deficient pasture had an increase in weight gain of 30-40kg/head/year. The response in breeders was recorded as the increase in weaning rates and increase in calf weights at weaning. On acutely deficient soils, the weaning percentage increased by 10-30% whereas the increase in weights at weaning increased by 10-20kg per head. Therefore, by meeting phosphorus requirements in the diet through supplementation will increase the cow's ability to produce a healthy calf each year, thus increasing productivity and profitability.

My soils are relatively fertile; do I really need to supplement phosphorus in the wet?

Data from MLA (2007) on the nutrient requirements of breeders shows that not only do the energy and protein requirements significantly increase from late pregnancy to late lactation but the mineral requirements also increase. As heifers still have a high nutrient requirement for their own growth as well as the growth of the foetus/calf it is important to help maintain her pre-pregnancy condition as best as possible to ensure she has a better chance of conceiving again following calving.

Even though your soils may be relatively fertile, it is important to remember that heifers' high nutrient requirements for pregnancy coincide with the driest part of the year. Therefore, even if the pasture has a reasonable nutritional value, only about half of this will be digestible during the winter and so the heifer will only be getting half the nutrients she would normally get in the green season.

How can Top Country improve your breeder performance?

Depending on what the weather decides to do in the next few months will greatly affect your supplementing regime. There have been extensive studies conducted on the benefits of phosphorus supplementation in the wet with various properties up North achieving up to a 10% increase in weaning percentages.

Top Wet is a wet season mineral supplement containing 9% phosphorus and about 12% calcium to help breeders meet their high phosphorus requirements during the later stages of lactation on green feed. Top Wet targets consumptions at 100g per head per day; therefore at a cost of $904/t + GST, it only costs 9-10 cents per cow each day.

As you can see, it is very affordable to supplement phosphorus during the wet season with the triple benefit of heavier calves at weaning, improved breeder condition and potentially higher conception rates.

So if you would like to learn more about Top Wet or are interested in our other wet season supplements please don't hesitate to contact Top Country and speak to one of our qualified nutritionists today!


Author: Susie Doyle


SOURCE: Meat and Livestock Australia 2012, Phosphorus management of beef cattle in northern Australia, Meat & Livestock Australia Limited

Tags: BEEF cattle green feed dairy

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