Phosphorus nutrition and management - overcoming constraints to woder adoption

Dixon, Rob, Coates, David, Holmes, Bill, English, Bernie and Rolfe, Joe (2011). Phosphorus nutrition and management - overcoming constraints to woder adoption. In: Proceedings of the Northern Beef Research Update Conference. Northern Beef Research Update Conference, Darwin, Australia, (102-109). 3-4 August 2011.

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Author Dixon, Rob
Coates, David
Holmes, Bill
English, Bernie
Rolfe, Joe
Title of paper Phosphorus nutrition and management - overcoming constraints to woder adoption
Conference name Northern Beef Research Update Conference
Conference location Darwin, Australia
Conference dates 3-4 August 2011
Proceedings title Proceedings of the Northern Beef Research Update Conference
Place of Publication Park Ridge, QLD, Australia
Publisher North Australia Beef Research Council
Publication Year 2011
Sub-type Fully published paper
Start page 102
End page 109
Total pages 8
Collection year 2012
Language eng
Abstract/Summary The importance of phosphorus nutrition for cattle grazing northern Australian rangelands has been well documented and demonstrated. Phosphorus is clearly one of the most important nutritional deficiencies, within the limitations of potential metabolizable energy intakes, of grazing cattle in the seasonally dry tropics. Nevertheless it appears that only a small proportion of cattle grazing phosphorus deficient pastures are supplemented or otherwise managed to alleviate phosphorus deficiency. Estimated requirements for dietary phosphorus by various classes of cattle grazing tropical pastures have recently been revised (CSIRO 2007). The development of faecal near infrared spectroscopy F.NIRS) allows the routine estimation of metabolizable energy and nitrogen concentrations in the diet, and thus the potential productivity, of cattle grazing northern rangelands. The concentration of phosphorus in the diet of grazing cattle can be estimated from the concentration of phosphorus in the faeces, at least in cattle not fed phosphorus supplements. Combining estimates of diet metabolizable energy, nitrogen and phosphorus allows estimation whether current needs of the animal are supplied by the diet. Phosphorus-replete cattle have substantial body reserves of phosphorus which can be mobilized, especially in late pregnancy and lactation, to alleviate a dietary deficiency. However, these body reserves need to be replenished in late lactation or post-lactation if mobilization occurs each year. Diagnosis of subclinical phosphorus deficiency in grazing cattle, and prediction of animal responses to phosphorus supplements is difficult. In growing cattle the concentration of inorganic phosphorus in blood (Pi), in the late wet or early dry season, combined with information on diet metabolizable energy and nitrogen concentrations obtained by F.NIRS, provides the most reliable test. In pregnant or lactating cows measurements of faecal phosphorus concentration and F.NIRS provide the best estimate of whether phosphorus intake meets the current needs of the animal. However, estimates of adequacy of phosphorus supply need to also consider possible mobilization of body phosphorus reserves. Indicative responses to provision of phosphorus supplements by cattle grazing pastures ranging from marginal to acute deficiency are summarized. Economic evaluation of benchmark enterprises where cattle are expected to be phosphorus deficient indicate that phosphorus supplementation is highly cost-effective. Major obstacles to more widespread adoption of phosphorus supplementation appear to be lack of knowledge and appreciation by managers of the phosphorus status of their cattle, lack of appreciation of the cost-effectiveness of a phosphorus supplementation particularly for some classes of cattle, and the practical difficulties in implementing phosphorus supplementation during the wet season.
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Created: Wed, 12 Oct 2011, 14:19:50 EST by Dr Robert Dixon on behalf of Qld Alliance for Agriculture and Food Innovation