Phosphorus Management of Beef Cattle in Northern Australia

Abstract

Key messages for managing phosphorus nutrition
In many of regions of northern Australia, phosphorus (P) is a serious nutritional limitation to cattle production, reducing its efficiency and profitability.
Some general principles can be applied to strategies and practices when feeding phosphorus to beef cattle.
• The animals that need phosphorus most are growing stock, late-pregnant heifers and cows, and lactating cows.
• Deficient animals respond best to P supplement when their diet has adequate protein and energy. This is why P supplementation is most effective during the wet season.
• Signs of acute phosphorus deficiency include bone chewing, broken bones, peg-leg, poor body condition of breeders and botulism.
• There are no simple diagnostic tests for the P status of cattle. Blood and faecal P are the most useful indicators.
• If P is fed over the wet season on deficient country:
– young growing stock can increase their growth by 30–40kg/year
– breeders can increase weaning rates by 10–30%
• Deficiency is related to soil P status. As a general rule, where soil 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 breeders are likely to respond to feeding P
– exceed 8mg/kg, the economic benefit from feeding mature cows 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.
• Supplements should be compared on the cost of their P content, on the practicality of feeding out and on whether the animals will be able or willing to eat target amounts.
• A typical wet season loose-mix P supplement should contain at least 8% P; a typical dry season supplement will contain 2–4% P and also non-protein nitrogen (eg urea).
• On deficient country, lowering the stocking rate will not reduce the need to feed phosphorus.
• Where the native pasture on deficient country contains sufficient stylo, cattle may respond significantly to P supplement during the dry season because of the extra
protein in their diet.
• Because cattle eat more pasture when P supplements are fed, stocking rates should be reduced to avoid overgrazing.
• The economic benefits from feeding P are maximised when done in conjunction with other aspects of good herd management.