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Phosphorus diagnostic tool - validation and demonstration of a diagnostic tool for phosphorus status of beef cattle

Project start date: 01 May 2010
Project end date: 24 October 2014
Publication date: 20 April 2015
Project status: Completed
Livestock species: Grassfed cattle, Grainfed cattle
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Much of northern Australia is based on soils that are deficient in phosphorus (P), an essential nutrient for growing and breeder cattle. A robust test is required by industry to determine the P content of diets grazed by cattle.

This project aimed to validate the use of the ratio of the concentration of P in the faeces (FecP) to the metabolisable energy (ME) content (FecP:ME; mg P/MJ ME) of the diet as a diagnostic test for the adequacy of dietary P content in relation to energy intake and to determine the likely response of cattle to P supplementation. Feed intake, liveweight gain, the concentration of P in plasma (PiP), FecP and FecP:ME increased with increasing diet P content and P intake. Plasma inorganic P was the best indicator of P intake of steers consuming a high N, high ME diet and under grazing conditions.

The responses of FecP:ME and FecP:dietary N content to increasing diet P were similar when dietary ME and N content were constant. In a field experiment auto-drafters were used to draft cattle to allocated P supplement treatments in a single paddock. Under these extensive grazing conditions the FecP:ME indicated that indicator steers and breeders were P deficient but no response to P supplementation was evident and serum inorganic P concentration suggested that the indicator steers were not P deficient.
The FecP:ME may require further validation across a range of land types/pasture bases before it can be recommended for wide use by industry.

More information

Project manager: Nigel Tomkins
Primary researcher: University of Queensland