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Supplementing P-deficient beef herds

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

Breeders in late pregnancy or lactating breeders grazing dry season pastures in phosphorus-deficient country still have high P requirements.

For steers and heifers, providing additional supplementary phosphorus to animals on a protein deficient diet during the dry season can be detrimental if nitrogen (protein) is not included in the supplement. During the dry season, protein becomes the primary limiting nutrient and feeding a ‘P only’ supplement will not improve performance but can be detrimental and even induce bone fragility.

Supplementation guide

The quality of inorganic phosphorus supplements can vary depending on the source and how they’ve been made. It’s important to ask for an analysis of the supplement you choose and focus on the bioavailability of the phosphorus (what’s available to the animal), rather than the total amount.

As a general guide, mono-calcium phosphate (MCP) has the highest bioavailability, followed closely by mono-dicalcium phosphate (MDCP) and dicalcium phosphate (DCP). MDCP is a blend of MCP and DCP but isn’t always in the same proportions, which is why quality and pricing may vary.

If you use DCP, ensure it’s hydrous DCP so that it’s soluble in water – otherwise, it may be totally ineffective. Tricalcium phosphate (TCP) and rock phosphate aren’t recommended as supplements for cattle due to the extremely low bioavailability of phosphorus.

Top tips

  • Be aware that some sources of inorganic phosphorus may contain traces of heavy metals that may accumulate over an extended feeding period and could potentially show up in meat in rare and extreme cases.
  • Consider the best supplement system for your situation, such as loose mixes (covered lick sheds or exposed bulka bags), blocks or water medication.
  • Excessive amounts of calcium should be avoided.
  • Water medication systems can be impractical where alternative surface water is available.
  • In phosphorus-deficient high rainfall regions with sown pastures, phosphorus fertilisers are often more cost-effective than supplementing stock directly. In these situations, fertilisers increase pasture yields and diet quality.


Unlike urea supplementation, there’s no toxicity issue associated with phosphorus supplementation (unless urea is part of the supplement). The issue is not so much ‘over-supplementing’, but meeting the challenge of getting adequate phosphorus into cattle diets over the wet season when there’s more opportunity for increased weight gains.