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Summary – Why do cattle need phosphorus?

Cattle need phosphorus (P) for almost every vital function of the body. It’s used for:

  • building bones and teeth
  • metabolising fat, carbohydrates and protein
  • producing milk
  • maintaining feed intake, especially during the growing season.

Deficiencies often arise in tropical production systems because most northern soils have lower available soil P compared with southern Australia. This means there’s often insufficient P in the pasture to meet animal requirements.

The cattle that have the highest P requirements are growing stock, late-pregnant heifers and cows, and lactating cows.

The benefits of P

For many regions in northern Australia, P deficiency is a serious nutritional issue for beef herds and can cause major losses in productivity and profitability.

Research demonstrates that adequate phosphorus intake can:

  • increase birth weights by 6–12%
  • increase weaning rates by 15–30%
  • increase breeder cow live weights by up to 130kg
  • reduce breeder mortality rates by 15–50%.

How to identify a P deficiency

It’s not uncommon for beef producers to be unaware that a P problem exists in their herd. If stock are gaining weight and body condition is maintained once the wet season has started, there can be a misconception that stock are getting the nutrients they need from only pasture – which isn’t always the case.

Here are some ways to identify a P deficiency:

  • Clinical signs of deficiency include ‘peg leg’ where cattle develop an arched body, staggering gait and brittle bones. Serious production issues could be occurring long before clinical signs are identified in the herd.
  • Soil maps can provide a general indication of P deficiency.
  • Measuring the plasma inorganic phosphorus (PiP) levels of cattle that have not been fed P supplements for at least two weeks over the wet season is the best method to determine if the pastures are providing enough P (the P-Screen test).

The best time to supplement

All classes of cattle, whether they be steers, heifers or breeders, will benefit from phosphorus supplementation.

The response of the cattle depends on the severity of deficiency, class of animal and diet quality.

The greatest benefits from supplementation on deficient pastures are achieved over the wet season when grass is green and stock are gaining weight.

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