Phosphorus management of beef cattle in Northern Australia

Abstract

In many of regions of northern Australia, phosphorus (P) is a serious nutritional limitation to cattle production, reducing herd efficiency and profitability.
• Phosphorus (P) is an essential nutritional requirement in cattle.
• Many soils across northern Australia are deficient in P, thus pastures growing on these soils do not contain enough P for cattle nutritional requirements.
• Signs of acute phosphorus deficiency include bone chewing, broken bones, peg-leg, poor body condition of breeders and botulism.
• Deficient animals respond best to P when pastures contain adequate energy and protein for cattle growth and reproduction.
• Soil analysis of P analysed using the Colwell P test (bicarbonate extracted phosphorus) can determine P status of the soil (where different soil types are present in a paddock, all should be tested).
• Deficiency is related to soil P status. As a general rule, where soil Colwell P levels: » are deficient (5mg/kg or less), all classes of stock are likely to respond to feeding P » are marginal (6–8mg/kg), young cattle are likely to respond to feeding P »exceed 8mg/kg, the economic benefit from feeding P diminishes.
• Responses to P supplement may be lower if animals running on P-deficient country have access to adjacent areas of high-P soils, such as frontage country.
• There are no simple diagnostic tests for the P status of cattle. Soil, blood and faecal P are useful indicators.
• A blood test for plasma inorganic phosphorus (PIP) should ideally be combined with diet quality measured by Faecal Near Infrared Reflectance Spectroscopy (F.NIRS) analysis of dung samples.
• Cattle grazing P-deficient pastures require a P supplement to meet their nutritional requirements, relying on bone mobilisation of P will erode herd productivity.
• Cattle grazing deficient pastures and fed an effective P supplement will eat 10–30% more pasture (deficient cattle have a depressed intake).
• If P is fed over the wet season on deficient country: » young growing stock can increase their growth by up to 90kg above base growth »breeders can increase weaning rates by 10–30% and mature breeders can maintain an additional 100kg over the wet season.
• Stocking rates must be matched to carrying capacity to ensure cattle have enough pasture for requirements.
• Supplement blocks and loose licks each have merits – to attain production goals, cattle must eat it. Monitor intakes and adjust recipe when required to avoid wasting money on supplement that sits in the paddock.
• On deficient pastures, wet season supplement intakes should aim to provide at least 6g P/head/ day to young growing cattle and 10g P/head/day to breeders.
• Dry season supplement mixes should contain a source of protein (e.g. urea) with sufficient P content to provide 2–5g P per day per animal.
• The economic benefits from feeding P are maximised when done in conjunction with other aspects of good herd management.
• Order P supplement early and make realistic calculations for how much P you need to last the entire wet season.