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This article in JEQ

  1. Vol. 29 No. 1, p. 28-36
    Received: Nov 13, 1998

    * Corresponding author(s): h.valk@id.wag-ur.nl
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Prospects for Minimizing Phosphorus Excretion in Ruminants by Dietary Manipulation

  1. H. Valk *,
  2. J. A. Metcalf and
  3. P. J. A. Withers
  1. D LO-Institute for Animal Science and Health, ID-DLO, PO Box 65, 8200 AB, Lelystad, The Netherlands;
    B orregaard UK Ltd., Clayton Rd., Risley, Warrington, Cheshire WA3 6QQ UK;
    A DAS Bridgets, Martyr Worthy, Winchester, Hampshire SO21 1AP UK.



In most intensive dairy farms, P input exceeds output, causing potential P losses to the environment, which results in leaching to ground water and eutrophication. Phosphorus in fertilizer and purchased feeds are the main contributors to P input, whereas milk P is the main output. In the Netherlands, new legislation has been introduced to substantially reduce P surpluses. However, since P is essential for maintenance and milk production, the dietary P supply must be maintained, especially for high-yielding dairy cows. This paper reviews how dairy cow diets can be manipulated to reduce potential P-loss to the environment without negative effects on animal health, feed intake, or milk production. The availability of P in forages, purchased feed, and inorganic phosphate supplements for ruminants may differ substantially and more research work is needed to elucidate the relevant factors influencing feed P availability. There is a lack of understanding of how and to what extent P is absorbed from the small intestine and the relationship to hydrolysis and microbial P utilization in the rumen. Comparing national P requirement systems indicates that the systems used in the UK and Italy should be revised to minimize unnecessary P accumulation in the soil. In addition, the impact of manipulating the dietary P supply to decrease P losses from dairy farming systems is evaluated. Whole farm system studies have illustrated the potential environmental benefits of more closely monitoring imports of purchased feeds onto the farm.

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